Phase-specific lower limb kinematic differences during Taekwondo roundhouse kicks between elite and youth athletes revealed by 1D statistical parametric mapping

Phase-specific lower limb kinematic differences during Taekwondo roundhouse kicks between elite and youth athletes revealed by 1D statistical parametric mapping | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Phase-specific lower limb kinematic differences during Taekwondo roundhouse kicks between elite and youth athletes revealed by 1D statistical parametric mapping Jianbo Sun, Xing Lv, Gang Sun, Panpan Wang, Liang Yin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8535585/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To delineate youth–elite differences in roundhouse-kick technique, we quantified kinematic gaps and defined youth joint-motion patterns to guide training. Twenty-three elite and 23 youth athletes performed roundhouse kicks recorded with a 12-camera Vicon system (200 Hz). Support- and kicking-limb hip, knee, and ankle angles (Cardan XYZ) were filtered (zero-lag 4th-order Butterworth, 15 Hz), time-normalised to 0–100% (101 points; four phases & five events), and compared using 1D-SPM independent t-tests (RFT, α = 0.05). Differences were phase-specific. Hip: elites were more extended at support 25–35% (p = 0.008) and 40–45% (p = 0.040), and kicking 0–14% (p = 0.005); more support abduction at 40–65% (p < 0.01) and 88–100% (p = 0.004), but more kicking adduction at 0–3% (p = 0.041); smaller hip internal rotation (support p ≤ 0.007; kicking p < 0.001). Knee: greater support flexion at 95–100% (p = 0.015) and smaller kicking internal rotation at 2–9% (p = 0.002), 43–47% (p = 0.003), and 90–100% (p < 0.001). Ankle: elites were more plantarflexed at support 16–22% (p = 0.040) and 58–100% (p < 0.01), and kicking 57–93% (p < 0.01); kicking ankle abduction–adduction differed at 0–8% (p = 0.008). Elites adopt a more stable support posture and tighter rotation and braking, enabling rapid re-stabilisation; these windows are actionable targets for youth technique training. Health sciences/Anatomy Health sciences/Health care Health sciences/Medical research Biological sciences/Physiology Kinematics 1D-SPM Taekwondo Roundhouse kick Athlete Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Taekwondo is an Olympic combat sport in which scoring success depends heavily on fast and accurate lower-limb kicking techniques, particularly the roundhouse kick. The roundhouse kick is the most frequently used and one of the most effective scoring techniques in competition, and its execution requires coordinated multi-joint motions of the hip, knee and ankle to generate high foot velocity while maintaining postural stability [ 1 , 2 ] . Developing efficient roundhouse kick technique during adolescence is critical, because this stage represents a sensitive period for motor learning and the transition from youth to elite performance. Numerous biomechanical studies have examined the roundhouse kick to identify kinematic and kinetic determinants of performance, such as peak foot velocity, execution time, impact force, and joint angles at selected instants [ 3 – 5 ] . These investigations have provided valuable insights into how factors like stance position, target height, or execution style influence kicking performance, and some have compared athletes with different experience levels. However, most of this work relies on discrete outcomes extracted from continuous time-series—typically peak values or variables sampled at a few key events. While convenient, discrete analysis compresses the rich information contained in the full kinematic waveforms into a small number of points, which may obscure when during the movement differences between groups actually occur and can increase the risk of inconsistent inferences due to multiple testing [ 6 ] . One-dimensional Statistical Parametric Mapping (1D SPM) has emerged as a powerful alternative for analysing biomechanical time-series. SPM treats kinematic or kinetic waveforms as one-dimensional random fields and applies random field theory to perform hypothesis tests across the entire movement cycle, while controlling the family-wise error rate [ 7 , 8 ] . This approach preserves the temporal structure of the data and yields phase-specific clusters where significant differences occur, rather than a single global test statistic. Recent reviews highlight the growing use of spm1d in sports biomechanics for tasks such as gait analysis [ 9 ] , running [ 10 ] , landing and strength exercises [ 11 ] , but also emphasise that many sports-specific skills and populations remain under-represented [ 12 – 14 ] . Studies directly comparing discrete (0D) and continuous (1D) analyses further demonstrate that SPM can reveal temporal differences that are missed when only discrete metrics are considered [ 15 ] . In taekwondo, biomechanical studies of the roundhouse kick have mainly described kinematic patterns or discrete variables under different target conditions, stance configurations or limb dominance. Extending this work to the analysis of continuous lower-limb joint kinematics across the whole kick cycle can provide a more detailed picture of how movement is organised in athletes of different expertise [ 16 ] . By identifying which joints and phases of the kick systematically differ between elite and youth competitors, coaches can refine their technical models for talent development, deliver more phase-specific feedback, and individualise training tasks [ 17 , 18 ] . In practice, such information may support more efficient skill acquisition in youth athletes, contribute to raising their competitive level and increase the likelihood that promising juniors successfully progress to elite performance. Therefore, the aim of the present study was to use one-dimensional Statistical Parametric Mapping (1D SPM) to compare phase-normalized lower-limb joint kinematics during roundhouse kicks between elite and youth taekwondo athletes. Specifically, we analysed three-dimensional hip, knee and ankle joint angle waveforms of both the kicking and support limbs (X, Y and Z rotations) across the entire kick cycle. This comprehensive waveform approach was intended to identify phase-specific regions where joint motion patterns differ between performance levels, thereby providing a detailed technical map of how elite athletes organise multi-joint and inter-limb coordination during the roundhouse kick. We hypothesised that, compared with youth athletes, elite athletes would exhibit more efficient and coordinated three-dimensional hip–knee–ankle motion in both limbs—characterised by phase-specific differences in joint flexion–extension, abduction–adduction and rotation—leading to multiple temporal regions of significant group differences in lower-limb kinematics. 2. Methods 2.1. Participants This study was approved by the Ethics Committee of Universiti Sains Malaysia (USM/JEPeM/ 25030312), and all procedures conformed to the Declaration of Helsinki. Written informed consent was obtained from all participants and, for youth athletes under 18 years of age, from their legal guardians. An a priori power analysis was performed using G*Power 3.1 for a two-tailed independent-samples t-test comparing elite and youth taekwondo athletes. Assuming a large standardized effect size (Cohen’s d = 0.80) based on previous taekwondo biomechanics research, an α error probability of 0.05, a desired statistical power (1−β) of 0.80, and equal group sizes, the required total sample size was 52 participants (26 athletes per group). Briefly, elite athletes were 26.0 ± 1.4 years old, with a body height of 183.4 ± 3.8 cm and body mass of 68.8 ± 7.0 kg, whereas youth athletes were 15.6 ± 1.0 years old, with a body height of 173.1 ± 4.1 cm and body mass of 53.7 ± 5.3 kg. All participants were right-leg dominant, determined by self-report as the preferred kicking leg. Elite athletes were included if they: (i) placed in the top three at national competitions or ranked within the top eight at international competitions; (ii) were aged 18–28 years; (iii) had ≥6 years of taekwondo training; and (iv) were free from injury and substance dependence. Youth athletes were included if they: (i) placed in the top three at Shandong provincial competitions or won a championship at Yantai city-level competitions; (ii) were aged 14–17 years; (iii) had ≥2 years of taekwondo training; and (iv) were free from injury and substance dependence. 2.2. Experimental procedures Before testing, participants completed a standardized warm-up consisting of light jogging, dynamic stretching and several submaximal practice kicks. For the measurement trials, each athlete stood in a taekwondo fighting stance with the feet placed in an anterior–posterior position, with one foot in front of the other. The stance was standardised so that the right (dominant) leg was the rear leg used for kicking and the left leg served as the support limb. Participants performed rear-leg roundhouse kicks using their right (kicking) limb, striking a hand-held target positioned in front of the athlete. The target was held by an experienced coach at the height of the athlete’s trunk to simulate a typical scoring region in competition [19] . Each participant performed three maximal rear-leg roundhouse kicks under the same conditions [20] . A 60 s rest interval was provided between trials to minimise the influence of fatigue. Trials in which the athlete slipped, missed the target or failed to follow the prescribed technique were discarded. For each participant, all remaining valid trials (up to three) were retained, time-normalised, and averaged to obtain a single representative waveform per variable for subsequent kinematic processing and 1D SPM analysis. If fewer than three valid trials remained, the average was computed across the available trials. 2.3. Measurement of roundhouse kick kinematics Three-dimensional lower-limb kinematics were recorded using a 12-camera motion analysis system (Vicon Motion Systems Ltd., Oxford, UK) sampling at 200 Hz. The capture volume was centred on the area occupied by the two force plates and the kicking space. Prior to data collection, the system was calibrated according to the manufacturer’s guidelines, and the residual calibration error was maintained below 1 mm. Retroreflective markers (14mm diameter) were attached to anatomical landmarks by the same experienced investigator. Markers were placed bilaterally on the anterior and posterior superior iliac spines, greater trochanters, lateral and medial femoral epicondyles, lateral and medial malleoli, heel, and the heads of the first and fifth metatarsals. Additional clusters were fixed to the thighs and shanks to improve tracking during high-velocity kicking. A static calibration trial in an upright anatomical position was collected to define segment coordinate systems and joint centres. The hip joint centre was estimated using a predictive regression method, and the knee and ankle joint centres were defined as the midpoints between the respective medial and lateral markers [21] . Lower-limb joint angles (hip, knee and ankle) of both the support and kicking limbs were expressed using a Cardan X-Y-Z rotation sequence (flexion–extension, abduction–adduction, internal–external rotation), in accordance with International Society of Biomechanics recommendations for lower-extremity joint kinematics [22] . Positive values indicated flexion, and negative values indicated extension for the flexion–extension degree of freedom. For the abduction–adduction degree of freedom, negative values indicated abduction and positive values indicated adduction. For the internal–external rotation degree of freedom, positive values indicated internal rotation and negative values indicated external rotation. Key events of the roundhouse kick were identified from the 3D kinematic data. 2.4 Kinematic data processing and phase definition All kinematic data were processed within the Vicon Nexus (Version 2.12, Oxford Metric Group). Marker trajectories were used low pass fourth-order Butterworth filter with 10 Hz cutoff frequency for each trial. For each participant, each valid trial was time-normalised to 101 points (0–100% of the kick cycle) using linear interpolation [23,24] . The time-normalised waveforms were then averaged across trials to create a single participant-level waveform for subsequent analyses. Five key events (Fig.1) were used to define the time-normalised kick cycle (0–100%) based on three-dimensional motion-capture data. Events were identified from the kinematics of the kicking limb. E1 (Initiation) was defined as the first instant the kicking foot started moving, identified when the resultant velocity of a representative kicking-foot marker exceeded 0.20 m/s and remained above this threshold for at least 25 ms (to avoid noise-related crossings). E2 (Chamber) was defined as the instant of maximum knee flexion of the kicking limb after E1. E3 (Peak knee extension) was defined as the instant of maximum knee extension during the kicking action, operationalised as the minimum knee-flexion angle after E2. Because foot–target contact was not instrumented in the present set-up, E3 should be interpreted as a kinematic proxy for the striking moment rather than the exact instant of contact. E4 (Retraction) was defined as the instant of maximum knee flexion during leg retraction after E3. E5 (End) was defined as the first instant after E4 when the vertical position of the kicking-foot marker reached a local minimum and the resultant foot velocity remained below 0.10 m/s for at least 50 ms, indicating completion of landing and stabilisation. The kick cycle was time-normalised from E1 to E5 and resampled to 101 points for subsequent analyses. Accordingly, the four phases were defined as P1 (E1–E2), P2 (E2–E3), P3 (E3–E4), and P4 (E4–E5). 2.5 Statistical analysis For each waveform, random field theory was used to determine a two-tailed critical threshold (±t*) controlling the family-wise error rate at α = 0.05 across the 0–100% temporal domain [25,26] . Supra-threshold regions where SPM{t} exceeded the critical threshold were identified as clusters, and cluster-level p-values were computed using random field theory [26] . Given the exploratory nature of testing multiple waveforms (3 joints × 3 degrees of freedom × 2 limbs = 18), we additionally controlled for multiple comparisons across waveforms using the Benjamini–Hochberg false discovery rate (FDR) procedure with q = 0.05. To implement cross-waveform FDR control, a single waveform-level p-value (p_wave) was defined as the smallest RFT cluster-level p-value observed within that waveform; when no supra-threshold clusters were present, p_wave was set to 1.0. The set of p_wave values (m = 18) was then adjusted using BH-FDR, and a waveform was considered statistically significant only if it contained at least one supra-threshold cluster and its FDR-adjusted q-value was 0) indicated larger joint-angle values in the elite group than in the youth group, whereas negative SPM{t} values (SPM{t} < 0) indicated larger joint-angle values in the youth group. Positive values indicated flexion at the hip and knee and dorsiflexion at the ankle; negative values indicated extension at the hip and knee and plantarflexion at the ankle. For the abduction–adduction degree of freedom, negative values indicated abduction and positive values indicated adduction. For each significant cluster, onset and offset were reported as percentages of the kick cycle [28] . 3. Results 3.1 Hip joint kinematics Figure 2 shows time-localized between-group differences in kicking- and support-limb hip joint kinematics across the normalized roundhouse-kick cycle (0–100%), as revealed by one-dimensional SPM analysis in elite and youth athletes. Significant differences were observed over specific time intervals for hip extension, abduction–adduction, and external–internal rotation in both the support and kicking limbs. No significant between-group differences were detected for the remaining hip kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold. 3.1.1 Hip flexion–extension (support and kicking limbs) One-dimensional SPM revealed significant between-group differences in hip flexion–extension during discrete portions of the kick cycle (Fig. 2a–d). For the support limb, the SPM{t} trajectory fell below the negative critical threshold at 25–35% ( p = 0.008, t* = 3.208, Fig. 2b) and 40–45% ( p = 0.040, Fig. 2b), indicating smaller hip flexion–extension angles in elite athletes than in youth athletes over these intervals (t < 0). Under the present sign convention (positive values indicate hip flexion), these negative clusters correspond to a less flexed (more extended) support-hip posture in elite athletes (Fig. 2a). For the kicking limb, a significant negative cluster was observed at 0–14% ( p = 0.005, t* = 3.159 , Fig. 2d), likewise indicating smaller hip flexion–extension angles in elite athletes (t < 0) and therefore reduced hip flexion (a more extended/less flexed kicking-hip posture) during the early preparation phase (Fig. 2c). No additional supra-threshold clusters were detected, and no further between-group differences were observed across the remainder of the kick cycle. 3.1.2 Hip abduction–adduction (support and kicking limbs) One-dimensional SPM identified discrete between-group differences in hip abduction–adduction (Fig. 2e–h). For the support limb (Fig. 2e–f), the SPM{t} trajectory crossed the negative critical threshold during the mid portion of the kick cycle (40–65%, p < 0.01, t* = 3.227) and again during the late portion of the kick cycle (88–100%, p = 0.004), indicating smaller abduction–adduction angles in elite athletes than in youth athletes over these intervals (t < 0). Under the present sign convention for this degree of freedom (negative values indicate hip abduction), these negative clusters correspond to a more abducted support-hip posture in elite athletes during mid-cycle and near the end of the cycle. For the kicking limb (Fig. 2g–h), an early positive supra-threshold cluster was observed at 0–3% (p = 0.041, t* = 3.161), indicating larger abduction–adduction angles in elite athletes (t > 0). Given the same sign convention, this pattern is consistent with a less abducted (more adducted) hip position at movement onset. No additional supra-threshold clusters were detected outside these intervals. 3.1.3 Hip internal–external rotation (support and kicking limbs) One-dimensional SPM identified discrete between-group differences in hip internal–external rotation (Fig. 2[i–l]). For the support limb (Fig. 2[i–j]), the SPM{t} trajectory exceeded the negative critical threshold (t* = 3.223) across multiple clusters (early cycle: p = 0.007; mid-cycle and late-cycle: p < 0.001), indicating that elite athletes exhibited smaller internal–external rotation angles than youth athletes over these supra-threshold intervals (t < 0). Under the present sign convention for this degree of freedom (positive = internal rotation; negative = external rotation), these negative clusters correspond to a less internally rotated (i.e., relatively more externally rotated) support-hip posture in the elite group during those portions of the kick cycle. For the kicking limb (Fig. 2[k–l]), one prominent negative supra-threshold cluster was observed in the mid-to-late part of the kick cycle (p < 0.001) with a critical threshold of t* = 3.315, likewise indicating smaller internal–external rotation angles in elite athletes (t < 0) and, therefore, reduced internal rotation (a shift toward external rotation) during that interval. No additional supra-threshold clusters were detected outside these regions. 3.2 Knee joint kinematics Figure 3 presents time-localized between-group differences in kicking- and support-limb knee joint kinematics across the normalised roundhouse-kick cycle (0–100%), as revealed by one-dimensional SPM analysis in elite and youth athletes. The results showed significant differences over brief time intervals for support-limb knee flexion–extension and kicking-limb knee internal–external rotation. No significant between-group differences were detected for the remaining knee kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold. 3.2.1 Knee flexion–extension (support limbs) One-dimensional SPM identified a terminal between-group difference in support-limb knee flexion–extension (Fig. 3[a–b]). Specifically, the SPM{t} trajectory exceeded the positive critical threshold (t* = 3.222) during the final portion of the kick cycle (95–100%, p = 0.015), indicating larger knee flexion–extension angles in elite athletes than in youth athletes over this interval (t > 0). Under the present sign convention (positive values denote knee flexion), this corresponds to a more flexed (less extended) support-knee posture in elite athletes during the late landing–stabilisation period approaching the end of the cycle. No additional supra-threshold clusters were detected outside this region. No supra-threshold clusters were observed for kicking-limb knee flexion–extension. 3.2.2 Knee internal–external rotation (kicking limb) One-dimensional SPM demonstrated multiple between-group differences in kicking-limb knee internal–external rotation (Fig. 3[e–f]). The SPM{t} trajectory fell below the negative critical threshold (t* = 3.409) at the very beginning of the kick cycle (2–9%, p = 0.002) and again during the mid-cycle period (43–47%, p = 0.003), indicating smaller knee internal–external rotation angles in elite athletes than in youth athletes over these intervals (t < 0). Under the present sign convention (positive values denote knee internal rotation), these negative clusters correspond to smaller knee internal rotation (i.e., a more externally rotated/less internally rotated knee orientation) in elite athletes during early initiation and around the striking window. In contrast, a further negative supra-threshold cluster was observed in the late portion of the cycle (90–100%, p < 0.001), likewise indicating smaller knee internal–external rotation angles in elite athletes (t < 0) and therefore reduced knee internal rotation as the movement approached completion. No additional supra-threshold regions were detected outside these discrete intervals. 3.3 Ankle joint kinematics Figure 4 shows time-localized between-group differences in kicking- and support-limb ankle joint kinematics across the normalized roundhouse-kick cycle (0–100%) in elite and youth athletes. Significant differences were observed over brief time intervals for ankle dorsiflexion–plantarflexion in both the support and kicking limbs, as well as for kicking-limb ankle abduction–adduction. No significant between-group differences were detected for the remaining ankle kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold. 3.3.1 Ankle dorsiflexion–plantarflexion (support and kicking limbs) One-dimensional SPM revealed phase-specific between-group differences in ankle dorsiflexion–plantarflexion for both limbs (Fig. 4[a–d]). For the support limb (Fig. 4[a–b]), the SPM{t} trajectory fell below the negative critical threshold (t* = 3.174) at 16–22% of the kick cycle (p = 0.04) and again during a prolonged late-cycle interval (58–100%, p < 0.01), indicating smaller ankle dorsiflexion–plantarflexion angles in elite athletes than in youth athletes over these intervals (t < 0). Under the present sign convention (positive = dorsiflexion; negative = plantarflexion), these negative clusters correspond to reduced dorsiflexion (i.e., a more plantarflexed support-ankle posture) in elite athletes during mid-cycle and toward the end of the movement. For the kicking limb (Fig. 4[c–d]), the SPM{t} trajectory likewise dropped below the negative threshold (t* = 3.379) across a broad late-cycle interval (57–93%, p < 0.01), indicating smaller dorsiflexion–plantarflexion angles in elite athletes during this period (t < 0). Interpreted with the same sign convention, this reflects a less dorsiflexed (more plantarflexed) kicking-ankle posture in elite athletes across the later phases of the kick cycle. No additional supra-threshold clusters were detected outside these regions. 3.3.2 Ankle abduction–adduction (kicking limb) One-dimensional SPM indicated a brief, early between-group difference in kicking-limb ankle abduction–adduction (Fig. 4[e–f]). The SPM{t} trajectory fell below the negative critical threshold (t* = 3.296) during 0–8% of the kick cycle (p = 0.008), indicating smaller abduction–adduction angles in elite athletes than in youth athletes over this interval (t < 0). Outside this initial supra-threshold cluster, the SPM{t} trajectory did not exceed ±t*, and no further between-group differences were detected across the remainder of the kick cycle. 4. Discussion This study applied one-dimensional statistical parametric mapping (1D SPM) to test hypotheses on lower-limb joint-angle waveforms during the roundhouse kick, enabling a whole-cycle comparison of kinematic patterns between elite and youth taekwondo athletes. The observed group differences were not uniformly distributed across the kick cycle; instead, they were concentrated within a set of task-relevant windows, primarily around preparation, impact/striking, and retraction–landing stabilisation. Collectively, these windows reflect sequential control demands associated with establishing a stable force-production platform, accelerating the distal segments toward the target, and rapidly retracting and re-stabilising to resume a combat-ready posture. For hip flexion–extension, the support limb showed two significant between-group intervals that aligned with E2 (chamber) and E3 (impact), with elite athletes exhibiting a more extended (less flexed) hip posture than youth athletes. This pattern is consistent with a “support-side platform” strategy: a more extended support hip during chambering and impact may help maintain pelvic–trunk alignment [29] , reduce energy leakage associated with excessive collapse on the support side, and provide a more stable base from which the kicking limb can accelerate [30] . The kicking limb also demonstrated a more extended posture in the early initiation period in elite athletes, suggesting a more compact initiation strategy that relies less on large preparatory hip flexion and more on a direct limb path with tighter temporal organisation—features that may support better concealment and faster onset [12] . The lack of differences outside these windows implies broadly similar baseline waveform shapes across substantial portions of the cycle, with expertise differences expressed primarily through phase-specific posture and timing control rather than a wholesale change in kinematic “style.” For hip abduction–adduction, significant differences emerged in the support limb during 40%–65% (early retraction after impact) and again in the terminal 88%–100% window, with elite athletes showing less adduction and greater abduction than youth athletes. Increased support-hip abduction during retraction may reflect more active control of pelvic stability and lower-limb alignment, helping to dampen lateral sway and preserve a controllable base for landing and re-stabilisation [31] . The persistence of this abducted pattern late in the cycle likely represents continued stabilisation after foot return, potentially facilitating faster posture recovery and reduced centre-of-mass drift. Notably, the kicking limb displayed an opposite early-phase pattern (first 5%), with elite athletes showing greater adduction and less abduction, consistent with a “tightening” of the outgoing limb path before acceleration—potentially limiting unnecessary lateral deviation at initiation and promoting a cleaner trajectory into the subsequent whip-like segmental acceleration [32] . For hip internal–external rotation, the support limb exhibited multiple significant intervals spanning movement onset, the chamber-to-impact transition, and post-impact retraction, with elite athletes showing smaller internal rotation (i.e., a more externally rotated posture) overall. This suggests a more restrained trade-off between generating rotation and maintaining support-side stability: avoiding excessive hip internal rotation during phases that demand force transfer and direction change may help preserve controllable lower-limb alignment and pelvic posture, reducing the tendency to “shift” rotational demands distally toward the knee [33,34] . The kicking limb showed a similar reduction in internal rotation during early retraction, consistent with stronger rotational braking and quicker recovery into a stance that better supports continuous attack–defence transitions. For youth athletes, these findings argue against focusing only on “kicking faster”, instead, support-side rotational control, braking during retraction, and terminal re-stabilisation should be trained as distinct capacities to avoid slow recovery, post-impact instability, and disrupted action chaining in competition [35] . At the knee, the support-limb difference occurred at the end of the kick cycle (95–100%), where elite athletes showed greater knee flexion than youth athletes. This end-phase increase in knee flexion likely reflects a more controlled landing–stabilisation strategy, allowing elite performers to absorb impact, re-centre the body mass, and re-establish a combat-ready stance more efficiently [36] . In contrast, reduced terminal knee flexion in youth athletes may indicate a stiffer or less coordinated landing response, which could compromise post-kick stability and slow the transition into subsequent actions [37] , with potential implications for injury risk [38] . Consistent with this interpretation, prior work has reported associations between support-limb knee frontal-plane positioning and scoring-relevant performance indicators, suggesting that better mediolateral knee regulation contributes to a more stable base and effective striking [39] . In the kicking limb, knee transverse-plane behaviour also differed at key moments. Elite athletes exhibited smaller knee internal–external rotation values (i.e., reduced internal rotation under the present sign convention) during 2–9%, 43–47%, and 90–100% of the kick cycle. These discrete windows correspond to early initiation, the mid-cycle transition around the striking window, and terminal landing/end-phase stabilisation, respectively. Collectively, this pattern suggests tighter transverse-plane control of the kicking knee when the limb is being organised for acceleration, redirected for recovery, and re-stabilised after the kick [40] . For youth athletes, relatively greater knee internal rotation during these windows may reflect a more distal “compensation” strategy when proximal rotational control is less stable, potentially contributing to greater path variability and less decisive recovery [41] . For ankle dorsiflexion–plantarflexion, the support limb showed significant differences at 16–22% and across a prolonged late-cycle interval (58–100%), with elite athletes demonstrating a more plantarflexed posture (i.e., reduced dorsiflexion) than youth athletes. This may reflect a stiffer ankle–foot platform during early set-up as well as a more controlled re-stabilisation strategy during retraction and landing/end-phase [42] , which could facilitate faster balance recovery and readiness for follow-up actions. The kicking limb showed a similar plantarflexion-dominant difference during 57–93%, suggesting that elite athletes maintain a tighter foot posture through late recovery, potentially supporting a more compact return path and more consistent preparation for foot placement. Finally, a brief early between-group difference was observed for kicking-limb ankle abduction–adduction during 0–8% of the kick cycle, with elite athletes showing smaller abduction–adduction angle values than youth athletes. Given the present sign convention (negative = abduction; positive = adduction), this indicates an early-phase shift toward less adduction and/or a more abducted foot orientation in elite performers during initiation. Such an early foot-positioning strategy may help establish a consistent limb trajectory and facilitate a quicker transition into the subsequent chambering and striking actions [43] . The phase-specific nature of the between-group differences identified by 1D SPM suggests that technical development in youth athletes may benefit more from targeted, phase-driven interventions than from globally increasing joint-angle magnitudes [44] . Across the kick cycle, elite athletes tended to adopt a more “platform-like” support strategy during key windows, characterised by a less flexed support hip around chambering/strike execution, phase-dependent frontal-plane hip control toward the end of the cycle, and ankle posture modulation that was most evident during late recovery and landing–stabilisation. These patterns point to a movement solution that prioritises a stable proximal base for rotation and rapid distal repositioning, rather than relying on large preparatory excursions or late compensations. From a coaching perspective, three training emphases follow. First, support-side platform control should be trained explicitly: single-leg stance tasks with pelvic control constraints and real-time feedback can be integrated into kick drills to reduce collapse and improve alignment during the preparatory and striking windows. Second, youth athletes may benefit from compact initiation strategies, in which the early phase is coached to minimise unnecessary kicking-leg “over-lifting” and lateral detours, thereby improving concealment and shortening time-to-peak knee extension [45] . Third, because several between-group differences clustered in the recovery and terminal portions of the cycle, rapid recoil and landing–stabilisation should be treated as a technical skill in its own right (e.g., time-limited return-to-guard drills, coupled with a brief post-landing “freeze” criterion to enforce end-phase control). A common maladaptive habit in youth athletes is to hang the leg after the strike and re-land with visible sway, which delays the return to fighting stance and disrupts subsequent attack–defence transitions. A practical corrective cue is “retract first, stabilise second”: immediate kicking-leg retraction after impact, followed by controlled re-establishment of support-side alignment before initiating the next action. A limitation is that the striking event was defined kinematically (E3: peak knee extension) and may not coincide exactly with the instant of foot–target contact due to target compliance and individual technique. Therefore, interpretations referring to “impact” should be understood as occurring around the putative striking moment (around E3) rather than at a directly measured contact time. Future studies should incorporate an instrumented target or synchronised video based contact detection to identify contact timing directly. Conclusion Overall, 1D SPM demonstrated that expertise-related differences in the roundhouse kick were not global magnitude changes across the entire waveform, but were concentrated in discrete, task-critical windows surrounding strike execution and post-strike retraction–landing stabilisation. Relative to youth athletes, elite performers exhibited a more “platform-like” support strategy, characterised by a less flexed and less internally rotated support hip during key moments of force production and directional change, together with phase-dependent frontal-plane control that favoured a more abducted support-hip posture during retraction and terminal stabilisation. In the kicking limb, elite athletes showed reduced transverse-plane knee rotation at key moments, consistent with tighter rotational control during initiation, recovery, and end-phase stabilisation. At the ankle, elite athletes showed a more plantarflexed posture in the support limb during 16–22% and 58–100% of the cycle, and in the kicking limb during 57–93%, which may reflect a more rigid ankle–foot configuration and a faster return to a stable fighting stance. A brief early difference was also observed at movement onset in kicking-ankle abduction–adduction (0–8%). Collectively, these findings suggest that technical advancement from youth to elite performance is reflected less in uniformly larger joint excursions and more in phase-specific organisation of stability, rotation, and braking across the kinetic chain. Practically, coaching interventions for youth athletes may be most effective when targeting these key windows—training a stable support-side platform, controlling transverse-plane motion without “dumping” rotation to the knee, and improving kick recovery and landing re-stabilisation—to enhance action continuity and competitive effectiveness. Declarations Competing interests The authors declare no competing financial interests. Funding This research received no external funding. Author Contribution Author contributions: J.S. conceived the study. J.S. and L.Y. designed the experimental protocol. J.S. and X.L. recruited participants and collected motion-capture data. J.S. curated the dataset and performed signal processing. J.S.and X.L. implemented the analysis pipeline and performed statistical analyses. J.S., L.Y. and G.S. interpreted the findings. J.S. wrote the first draft. G.S. and P.W. edited and revised the manuscript. J.S. prepared the figures and tables. All authors reviewed and approved the final manuscript. Data Availability The datasets generated and analyzed during the current study are not publicly available due to participant privacy and institutional data protection policies but are available from the corresponding author upon reasonable request. References Estevan, I. & Falco, C. 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14:29:36","extension":"html","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":125161,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/2f9068dac048f46c15bb09b6.html"},{"id":100898253,"identity":"2af7fa09-9639-4961-913e-f29f52fd80ea","added_by":"auto","created_at":"2026-01-22 14:29:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":178699,"visible":true,"origin":"","legend":"\u003cp\u003eKey events and phases of the roundhouse kick cycle (0-100%)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/c72870227534eac5e26d1870.png"},{"id":100951133,"identity":"cff1d91d-2571-44af-bee7-e9e49d5d1f9e","added_by":"auto","created_at":"2026-01-23 07:10:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1265655,"visible":true,"origin":"","legend":"\u003cp\u003eHip joint kinematics of the support (left) and kicking (right) limbs during the roundhouse kick, with corresponding 1D statistical parametric mapping (SPM) results comparing elite and youth athletes. Left panels depict group mean ± SD hip-angle waveforms, and right panels show the corresponding SPM{t} trajectories across the time-normalised kick cycle (0–100%). Dashed red horizontal lines represent the critical threshold (t*) for a two-tailed test at α = 0.05. Grey shaded regions and annotated p-values indicate supra-threshold clusters where significant between-group differences were detected. The left limb served as the support limb and the right limb served as the kicking limb. Blue lines/shading: elite; red lines/shading: youth. (a–b) Support-limb hip flexion–extension: waveform and SPM{t}. (c–d) Kicking-limb hip flexion–extension: waveform and SPM{t}. (e–f) Support-limb hip abduction–adduction: waveform and SPM{t}. (g–h) Kicking-limb hip abduction–adduction: waveform and SPM{t}. (i–j) Support-limb hip internal–external rotation: waveform and SPM{t}. (k–l) Kicking-limb hip internal–external rotation: waveform and SPM{t}.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/8638d6205c32c9eed82afa12.png"},{"id":100898255,"identity":"679a7563-81d7-4253-b3df-8689d76b835a","added_by":"auto","created_at":"2026-01-22 14:29:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":388388,"visible":true,"origin":"","legend":"\u003cp\u003eKnee joint kinematics of the support (left) and kicking (right) limbs during the roundhouse kick, with corresponding 1D statistical parametric mapping (SPM) results comparing elite and youth athletes. Left panels show knee-angle waveforms, and right panels show the corresponding SPM{t} trajectories across the time-normalised kick cycle. (a–b) Support-limb knee flexion–extension: waveform and SPM{t}. (c–d) Kicking-limb knee flexion–extension: waveform and SPM{t}. (e–f) Kicking-limb knee internal–external rotation: waveform and SPM{t}.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/07077943ca680048c5b9e483.png"},{"id":100951204,"identity":"b4cb658e-bfdd-4a4e-8141-c9f016f7111f","added_by":"auto","created_at":"2026-01-23 07:10:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":603266,"visible":true,"origin":"","legend":"\u003cp\u003eAnkle joint kinematics of the support (left) and kicking (right) limbs during the roundhouse kick, with corresponding 1D statistical parametric mapping (SPM) results comparing elite and youth athletes. Left panels show ankle-angle waveforms, and right panels show the corresponding SPM{t} trajectories across the time-normalised kick cycle. (a–b) Support-limb ankle dorsiflexion–plantarflexion: waveform and SPM{t}. (c–d) Kicking-limb ankle dorsiflexion–plantarflexion: waveform and SPM{t}. (e–f) Kicking-limb ankle abduction–adduction: waveform and SPM{t}.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/0c2f2ee18e90cd8bf40f8049.png"},{"id":105702999,"identity":"b15013ce-ca64-4f10-9ee9-5640a2dbe422","added_by":"auto","created_at":"2026-03-30 06:27:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2762360,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8535585/v1/52aab2f1-1af3-487c-b92c-13a88b85c6a5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Phase-specific lower limb kinematic differences during Taekwondo roundhouse kicks between elite and youth athletes revealed by 1D statistical parametric mapping","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTaekwondo is an Olympic combat sport in which scoring success depends heavily on fast and accurate lower-limb kicking techniques, particularly the roundhouse kick. The roundhouse kick is the most frequently used and one of the most effective scoring techniques in competition, and its execution requires coordinated multi-joint motions of the hip, knee and ankle to generate high foot velocity while maintaining postural stability \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Developing efficient roundhouse kick technique during adolescence is critical, because this stage represents a sensitive period for motor learning and the transition from youth to elite performance.\u003c/p\u003e \u003cp\u003eNumerous biomechanical studies have examined the roundhouse kick to identify kinematic and kinetic determinants of performance, such as peak foot velocity, execution time, impact force, and joint angles at selected instants \u003csup\u003e[\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. These investigations have provided valuable insights into how factors like stance position, target height, or execution style influence kicking performance, and some have compared athletes with different experience levels. However, most of this work relies on discrete outcomes extracted from continuous time-series\u0026mdash;typically peak values or variables sampled at a few key events. While convenient, discrete analysis compresses the rich information contained in the full kinematic waveforms into a small number of points, which may obscure when during the movement differences between groups actually occur and can increase the risk of inconsistent inferences due to multiple testing \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eOne-dimensional Statistical Parametric Mapping (1D SPM) has emerged as a powerful alternative for analysing biomechanical time-series. SPM treats kinematic or kinetic waveforms as one-dimensional random fields and applies random field theory to perform hypothesis tests across the entire movement cycle, while controlling the family-wise error rate \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. This approach preserves the temporal structure of the data and yields phase-specific clusters where significant differences occur, rather than a single global test statistic. Recent reviews highlight the growing use of spm1d in sports biomechanics for tasks such as gait analysis \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e, running \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e, landing and strength exercises \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e, but also emphasise that many sports-specific skills and populations remain under-represented \u003csup\u003e[\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. Studies directly comparing discrete (0D) and continuous (1D) analyses further demonstrate that SPM can reveal temporal differences that are missed when only discrete metrics are considered \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn taekwondo, biomechanical studies of the roundhouse kick have mainly described kinematic patterns or discrete variables under different target conditions, stance configurations or limb dominance. Extending this work to the analysis of continuous lower-limb joint kinematics across the whole kick cycle can provide a more detailed picture of how movement is organised in athletes of different expertise \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. By identifying which joints and phases of the kick systematically differ between elite and youth competitors, coaches can refine their technical models for talent development, deliver more phase-specific feedback, and individualise training tasks \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. In practice, such information may support more efficient skill acquisition in youth athletes, contribute to raising their competitive level and increase the likelihood that promising juniors successfully progress to elite performance.\u003c/p\u003e \u003cp\u003eTherefore, the aim of the present study was to use one-dimensional Statistical Parametric Mapping (1D SPM) to compare phase-normalized lower-limb joint kinematics during roundhouse kicks between elite and youth taekwondo athletes. Specifically, we analysed three-dimensional hip, knee and ankle joint angle waveforms of both the kicking and support limbs (X, Y and Z rotations) across the entire kick cycle. This comprehensive waveform approach was intended to identify phase-specific regions where joint motion patterns differ between performance levels, thereby providing a detailed technical map of how elite athletes organise multi-joint and inter-limb coordination during the roundhouse kick. We hypothesised that, compared with youth athletes, elite athletes would exhibit more efficient and coordinated three-dimensional hip\u0026ndash;knee\u0026ndash;ankle motion in both limbs\u0026mdash;characterised by phase-specific differences in joint flexion\u0026ndash;extension, abduction\u0026ndash;adduction and rotation\u0026mdash;leading to multiple temporal regions of significant group differences in lower-limb kinematics.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1. Participants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Ethics Committee of Universiti Sains Malaysia (USM/JEPeM/ 25030312), and all procedures conformed to the Declaration of Helsinki. Written informed consent was obtained from all participants and, for youth athletes under 18 years of age, from their legal guardians.\u003c/p\u003e\n\u003cp\u003eAn a priori power analysis was performed using G*Power 3.1 for a two-tailed independent-samples t-test comparing elite and youth taekwondo athletes. Assuming a large standardized effect size (Cohen\u0026rsquo;s d = 0.80) based on previous taekwondo biomechanics research, an \u0026alpha; error probability of 0.05, a desired statistical power (1\u0026minus;\u0026beta;) of 0.80, and equal group sizes, the required total sample size was 52 participants (26 athletes per group). Briefly, elite athletes were 26.0 \u0026plusmn; 1.4 years old, with a body height of 183.4 \u0026plusmn; 3.8 cm and body mass of 68.8 \u0026plusmn; 7.0 kg, whereas youth athletes were 15.6 \u0026plusmn; 1.0 years old, with a body height of 173.1 \u0026plusmn; 4.1 cm and body mass of 53.7 \u0026plusmn; 5.3 kg. All participants were right-leg dominant, determined by self-report as the preferred kicking leg.\u003c/p\u003e\n\u003cp\u003eElite athletes were included if they: (i) placed in the top three at national competitions or ranked within the top eight at international competitions; (ii) were aged 18\u0026ndash;28 years; (iii) had \u0026ge;6 years of taekwondo training; and (iv) were free from injury and substance dependence.\u003c/p\u003e\n\u003cp\u003eYouth athletes were included if they: (i) placed in the top three at Shandong provincial competitions or won a championship at Yantai city-level competitions; (ii) were aged 14\u0026ndash;17 years; (iii) had \u0026ge;2 years of taekwondo training; and (iv) were free from injury and substance dependence.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2.\u0026nbsp;Experimental procedures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBefore testing, participants completed a standardized warm-up consisting of light jogging, dynamic stretching and several submaximal practice kicks. For the measurement trials, each athlete stood in a taekwondo fighting stance with the feet placed in an anterior\u0026ndash;posterior position, with one foot in front of the other. The stance was standardised so that the right (dominant) leg was the rear leg used for kicking and the left leg served as the support limb. Participants performed rear-leg roundhouse kicks using their right (kicking) limb, striking a hand-held target positioned in front of the athlete. The target was held by an experienced coach at the height of the athlete\u0026rsquo;s trunk to simulate a typical scoring region in competition \u003csup\u003e[19]\u003c/sup\u003e. Each participant performed three maximal rear-leg roundhouse kicks under the same conditions \u003csup\u003e[20]\u003c/sup\u003e. A 60 s rest interval was provided between trials to minimise the influence of fatigue. Trials in which the athlete slipped, missed the target or failed to follow the prescribed technique were discarded. For each participant, all remaining valid trials (up to three) were retained, time-normalised, and averaged to obtain a single representative waveform per variable for subsequent kinematic processing and 1D SPM analysis. If fewer than three valid trials remained, the average was computed across the available trials.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3.\u0026nbsp;Measurement of roundhouse kick kinematics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThree-dimensional lower-limb kinematics were recorded using a 12-camera motion analysis system (Vicon Motion Systems Ltd., Oxford, UK) sampling at 200 Hz. The capture volume was centred on the area occupied by the two force plates and the kicking space. Prior to data collection, the system was calibrated according to the manufacturer\u0026rsquo;s guidelines, and the residual calibration error was maintained below 1 mm.\u003c/p\u003e\n\u003cp\u003eRetroreflective markers (14mm diameter) were attached to anatomical landmarks by the same experienced investigator. Markers were placed bilaterally on the anterior and posterior superior iliac spines, greater trochanters, lateral and medial femoral epicondyles, lateral and medial malleoli, heel, and the heads of the first and fifth metatarsals. Additional clusters were fixed to the thighs and shanks to improve tracking during high-velocity kicking. A static calibration trial in an upright anatomical position was collected to define segment coordinate systems and joint centres. The hip joint centre was estimated using a predictive regression method, and the knee and ankle joint centres were defined as the midpoints between the respective medial and lateral markers \u003csup\u003e[21]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eLower-limb joint angles (hip, knee and ankle) of both the support and kicking limbs were expressed using a Cardan X-Y-Z rotation sequence (flexion\u0026ndash;extension, abduction\u0026ndash;adduction, internal\u0026ndash;external rotation), in accordance with International Society of Biomechanics recommendations for lower-extremity joint kinematics \u003csup\u003e[22]\u003c/sup\u003e. Positive values indicated flexion, and negative values indicated extension for the flexion\u0026ndash;extension degree of freedom. For the abduction\u0026ndash;adduction degree of freedom, negative values indicated abduction and positive values indicated adduction. For the internal\u0026ndash;external rotation degree of freedom, positive values indicated internal rotation and negative values indicated external rotation. Key events of the roundhouse kick were identified from the 3D kinematic data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Kinematic data processing and phase definition\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll kinematic data were processed within the Vicon Nexus (Version 2.12, Oxford Metric Group). Marker trajectories were used low pass fourth-order Butterworth filter with 10 Hz cutoff frequency for each trial. For each participant, each valid trial was time-normalised to 101 points (0\u0026ndash;100% of the kick cycle) using linear interpolation \u003csup\u003e[23,24]\u003c/sup\u003e. The time-normalised waveforms were then averaged across trials to create a single participant-level waveform for subsequent analyses.\u003c/p\u003e\n\u003cp\u003eFive key events (Fig.1) were used to define the time-normalised kick cycle (0\u0026ndash;100%) based on three-dimensional motion-capture data. Events were identified from the kinematics of the kicking limb. E1 (Initiation) was defined as the first instant the kicking foot started moving, identified when the resultant velocity of a representative kicking-foot marker exceeded 0.20 m/s and remained above this threshold for at least 25 ms (to avoid noise-related crossings). E2 (Chamber) was defined as the instant of maximum knee flexion of the kicking limb after E1. E3 (Peak knee extension) was defined as the instant of maximum knee extension during the kicking action, operationalised as the minimum knee-flexion angle after E2. Because foot\u0026ndash;target contact was not instrumented in the present set-up, E3 should be interpreted as a kinematic proxy for the striking moment rather than the exact instant of contact. E4 (Retraction) was defined as the instant of maximum knee flexion during leg retraction after E3. E5 (End) was defined as the first instant after E4 when the vertical position of the kicking-foot marker reached a local minimum and the resultant foot velocity remained below 0.10 m/s for at least 50 ms, indicating completion of landing and stabilisation. The kick cycle was time-normalised from E1 to E5 and resampled to 101 points for subsequent analyses. Accordingly, the four phases were defined as P1 (E1\u0026ndash;E2), P2 (E2\u0026ndash;E3), P3 (E3\u0026ndash;E4), and P4 (E4\u0026ndash;E5).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor each waveform, random field theory was used to determine a two-tailed critical threshold (\u0026plusmn;t*) controlling the family-wise error rate at \u0026alpha; = 0.05 across the 0\u0026ndash;100% temporal domain \u003csup\u003e[25,26]\u003c/sup\u003e. Supra-threshold regions where SPM{t} exceeded the critical threshold were identified as clusters, and cluster-level p-values were computed using random field theory \u003csup\u003e[26]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eGiven the exploratory nature of testing multiple waveforms (3 joints \u0026times; 3 degrees of freedom \u0026times; 2 limbs = 18), we additionally controlled for multiple comparisons across waveforms using the Benjamini\u0026ndash;Hochberg false discovery rate (FDR) procedure with q = 0.05. To implement cross-waveform FDR control, a single waveform-level p-value (p_wave) was defined as the smallest RFT cluster-level p-value observed within that waveform; when no supra-threshold clusters were present, p_wave was set to 1.0. The set of p_wave values (m = 18) was then adjusted using BH-FDR, and a waveform was considered statistically significant only if it contained at least one supra-threshold cluster and its FDR-adjusted q-value was \u0026lt; 0.05. For transparency, the original RFT cluster-level p-values and the corresponding FDR-adjusted q-values are reported \u003csup\u003e[27]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003ePositive SPM{t} values (SPM{t} \u0026gt; 0) indicated larger joint-angle values in the elite group than in the youth group, whereas negative SPM{t} values (SPM{t} \u0026lt; 0) indicated larger joint-angle values in the youth group. Positive values indicated flexion at the hip and knee and dorsiflexion at the ankle; negative values indicated extension at the hip and knee and plantarflexion at the ankle. For the abduction\u0026ndash;adduction degree of freedom, negative values indicated abduction and positive values indicated adduction. For each significant cluster, onset and offset were reported as percentages of the kick cycle \u003csup\u003e[28]\u003c/sup\u003e.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 Hip joint kinematics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 2 shows time-localized between-group differences in kicking- and support-limb hip joint kinematics across the normalized roundhouse-kick cycle (0\u0026ndash;100%), as revealed by one-dimensional SPM analysis in elite and youth athletes. Significant differences were observed over specific time intervals for hip extension, abduction\u0026ndash;adduction, and external\u0026ndash;internal rotation in both the support and kicking limbs. No significant between-group differences were detected for the remaining hip kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold.\u003c/p\u003e\n\u003cp\u003e3.1.1 Hip flexion\u0026ndash;extension (support and kicking limbs)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM revealed significant between-group differences in hip flexion\u0026ndash;extension during discrete portions of the kick cycle (Fig. 2a\u0026ndash;d). For the support limb, the SPM{t} trajectory fell below the negative critical threshold at 25\u0026ndash;35% (\u003cem\u003ep\u003c/em\u003e = 0.008, t* = 3.208, Fig. 2b) and 40\u0026ndash;45% (\u003cem\u003ep\u003c/em\u003e = 0.040, Fig. 2b), indicating smaller hip flexion\u0026ndash;extension angles in elite athletes than in youth athletes over these intervals (t \u0026lt; 0). Under the present sign convention (positive values indicate hip flexion), these negative clusters correspond to a less flexed (more extended) support-hip posture in elite athletes (Fig. 2a). For the kicking limb, a significant negative cluster was observed at 0\u0026ndash;14% (\u003cem\u003ep\u003c/em\u003e = 0.005, t* = 3.159 , Fig. 2d), likewise indicating smaller hip flexion\u0026ndash;extension angles in elite athletes (t \u0026lt; 0) and therefore reduced hip flexion (a more extended/less flexed kicking-hip posture) during the early preparation phase (Fig. 2c). No additional supra-threshold clusters were detected, and no further between-group differences were observed across the remainder of the kick cycle.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.1.2 Hip abduction\u0026ndash;adduction\u0026nbsp;(support and kicking limbs)\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM identified discrete between-group differences in hip abduction\u0026ndash;adduction (Fig. 2e\u0026ndash;h). For the support limb (Fig. 2e\u0026ndash;f), the SPM{t} trajectory crossed the negative critical threshold during the mid portion of the kick cycle (40\u0026ndash;65%, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01, t* = 3.227) and again during the late portion of the kick cycle (88\u0026ndash;100%, \u003cem\u003ep\u003c/em\u003e = 0.004), indicating smaller abduction\u0026ndash;adduction angles in elite athletes than in youth athletes over these intervals (t \u0026lt; 0). Under the present sign convention for this degree of freedom (negative values indicate hip abduction), these negative clusters correspond to a more abducted support-hip posture in elite athletes during mid-cycle and near the end of the cycle. For the kicking limb (Fig. 2g\u0026ndash;h), an early positive supra-threshold cluster was observed at 0\u0026ndash;3% (p = 0.041, t* = 3.161), indicating larger abduction\u0026ndash;adduction angles in elite athletes (t \u0026gt; 0). Given the same sign convention, this pattern is consistent with a less abducted (more adducted) hip position at movement onset. No additional supra-threshold clusters were detected outside these intervals.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.1.3 Hip internal\u0026ndash;external rotation (support and kicking limbs)\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM identified discrete between-group differences in hip internal\u0026ndash;external rotation (Fig. 2[i\u0026ndash;l]). For the support limb (Fig. 2[i\u0026ndash;j]), the SPM{t} trajectory exceeded the negative critical threshold (t* = 3.223) across multiple clusters (early cycle: p = 0.007; mid-cycle and late-cycle: p \u0026lt; 0.001), indicating that elite athletes exhibited smaller internal\u0026ndash;external rotation angles than youth athletes over these supra-threshold intervals (t \u0026lt; 0). Under the present sign convention for this degree of freedom (positive = internal rotation; negative = external rotation), these negative clusters correspond to a less internally rotated (i.e., relatively more externally rotated) support-hip posture in the elite group during those portions of the kick cycle. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the kicking limb (Fig. 2[k\u0026ndash;l]), one prominent negative supra-threshold cluster was observed in the mid-to-late part of the kick cycle (p \u0026lt; 0.001) with a critical threshold of t* = 3.315, likewise indicating smaller internal\u0026ndash;external rotation angles in elite athletes (t \u0026lt; 0) and, therefore, reduced internal rotation (a shift toward external rotation) during that interval. No additional supra-threshold clusters were detected outside these regions. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Knee joint kinematics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 3 presents time-localized between-group differences in kicking- and support-limb knee joint kinematics across the normalised roundhouse-kick cycle (0\u0026ndash;100%), as revealed by one-dimensional SPM analysis in elite and youth athletes. The results showed significant differences over brief time intervals for support-limb knee flexion\u0026ndash;extension and kicking-limb knee internal\u0026ndash;external rotation. No significant between-group differences were detected for the remaining knee kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.2.1 Knee flexion\u0026ndash;extension (support limbs)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM identified a terminal between-group difference in support-limb knee flexion\u0026ndash;extension (Fig. 3[a\u0026ndash;b]). Specifically, the SPM{t} trajectory exceeded the positive critical threshold (t* = 3.222) during the final portion of the kick cycle (95\u0026ndash;100%, \u003cem\u003ep\u003c/em\u003e = 0.015), indicating larger knee flexion\u0026ndash;extension angles in elite athletes than in youth athletes over this interval (t \u0026gt; 0). Under the present sign convention (positive values denote knee flexion), this corresponds to a more flexed (less extended) support-knee posture in elite athletes during the late landing\u0026ndash;stabilisation period approaching the end of the cycle. No additional supra-threshold clusters were detected outside this region. No supra-threshold clusters were observed for kicking-limb knee flexion\u0026ndash;extension.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.2.2 Knee internal\u0026ndash;external rotation (kicking limb)\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM demonstrated multiple between-group differences in kicking-limb knee internal\u0026ndash;external rotation (Fig. 3[e\u0026ndash;f]). The SPM{t} trajectory fell below the negative critical threshold (t* = 3.409) at the very beginning of the kick cycle (2\u0026ndash;9%, p = 0.002) and again during the mid-cycle period (43\u0026ndash;47%, p = 0.003), indicating smaller knee internal\u0026ndash;external rotation angles in elite athletes than in youth athletes over these intervals (t \u0026lt; 0). Under the present sign convention (positive values denote knee internal rotation), these negative clusters correspond to smaller knee internal rotation (i.e., a more externally rotated/less internally rotated knee orientation) in elite athletes during early initiation and around the striking window.\u003c/p\u003e\n\u003cp\u003eIn contrast, a further negative supra-threshold cluster was observed in the late portion of the cycle (90\u0026ndash;100%, p \u0026lt; 0.001), likewise indicating smaller knee internal\u0026ndash;external rotation angles in elite athletes (t \u0026lt; 0) and therefore reduced knee internal rotation as the movement approached completion. No additional supra-threshold regions were detected outside these discrete intervals. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Ankle joint kinematics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 4 shows time-localized between-group differences in kicking- and support-limb ankle joint kinematics across the normalized roundhouse-kick cycle (0\u0026ndash;100%) in elite and youth athletes. Significant differences were observed over brief time intervals for ankle dorsiflexion\u0026ndash;plantarflexion in both the support and kicking limbs, as well as for kicking-limb ankle abduction\u0026ndash;adduction. No significant between-group differences were detected for the remaining ankle kinematic degrees of freedom across the cycle, as the SPM{t} trajectories did not exceed the critical threshold.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.3.1 Ankle dorsiflexion\u0026ndash;plantarflexion (support and kicking limbs)\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM revealed phase-specific between-group differences in ankle dorsiflexion\u0026ndash;plantarflexion for both limbs (Fig. 4[a\u0026ndash;d]). For the support limb (Fig. 4[a\u0026ndash;b]), the SPM{t} trajectory fell below the negative critical threshold (t* = 3.174) at 16\u0026ndash;22% of the kick cycle (p = 0.04) and again during a prolonged late-cycle interval (58\u0026ndash;100%, p \u0026lt; 0.01), indicating smaller ankle dorsiflexion\u0026ndash;plantarflexion angles in elite athletes than in youth athletes over these intervals (t \u0026lt; 0). Under the present sign convention (positive = dorsiflexion; negative = plantarflexion), these negative clusters correspond to reduced dorsiflexion (i.e., a more plantarflexed support-ankle posture) in elite athletes during mid-cycle and toward the end of the movement.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the kicking limb (Fig. 4[c\u0026ndash;d]), the SPM{t} trajectory likewise dropped below the negative threshold (t* = 3.379) across a broad late-cycle interval (57\u0026ndash;93%, p \u0026lt; 0.01), indicating smaller dorsiflexion\u0026ndash;plantarflexion angles in elite athletes during this period (t \u0026lt; 0). Interpreted with the same sign convention, this reflects a less dorsiflexed (more plantarflexed) kicking-ankle posture in elite athletes across the later phases of the kick cycle. No additional supra-threshold clusters were detected outside these regions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.3.2 Ankle abduction\u0026ndash;adduction (kicking limb)\u003c/p\u003e\n\u003cp\u003eOne-dimensional SPM indicated a brief, early between-group difference in kicking-limb ankle abduction\u0026ndash;adduction (Fig. 4[e\u0026ndash;f]). The SPM{t} trajectory fell below the negative critical threshold (t* = 3.296) during 0\u0026ndash;8% of the kick cycle (p = 0.008), indicating smaller abduction\u0026ndash;adduction angles in elite athletes than in youth athletes over this interval (t \u0026lt; 0). Outside this initial supra-threshold cluster, the SPM{t} trajectory did not exceed \u0026plusmn;t*, and no further between-group differences were detected across the remainder of the kick cycle.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis study applied one-dimensional statistical parametric mapping (1D SPM) to test hypotheses on lower-limb joint-angle waveforms during the roundhouse kick, enabling a whole-cycle comparison of kinematic patterns between elite and youth taekwondo athletes. The observed group differences were not uniformly distributed across the kick cycle; instead, they were concentrated within a set of task-relevant windows, primarily around preparation, impact/striking, and retraction\u0026ndash;landing stabilisation. Collectively, these windows reflect sequential control demands associated with establishing a stable force-production platform, accelerating the distal segments toward the target, and rapidly retracting and re-stabilising to resume a combat-ready posture. For hip flexion\u0026ndash;extension, the support limb showed two significant between-group intervals that aligned with E2 (chamber) and E3 (impact), with elite athletes exhibiting a more extended (less flexed) hip posture than youth athletes. This pattern is consistent with a \u0026ldquo;support-side platform\u0026rdquo; strategy: a more extended support hip during chambering and impact may help maintain pelvic\u0026ndash;trunk alignment \u003csup\u003e[29]\u003c/sup\u003e,\u0026nbsp;reduce energy leakage associated with excessive collapse on the support side, and provide a more stable base from which the kicking limb can accelerate\u003csup\u003e[30]\u003c/sup\u003e. The kicking limb also demonstrated a more extended posture in the early initiation period in elite athletes, suggesting a more compact initiation strategy that relies less on large preparatory hip flexion and more on a direct limb path with tighter temporal organisation\u0026mdash;features that may support better concealment and faster onset \u003csup\u003e[12]\u003c/sup\u003e. The lack of differences outside these windows implies broadly similar baseline waveform shapes across substantial portions of the cycle, with expertise differences expressed primarily through phase-specific posture and timing control rather than a wholesale change in kinematic \u0026ldquo;style.\u0026rdquo; For hip abduction\u0026ndash;adduction, significant differences emerged in the support limb during 40%\u0026ndash;65% (early retraction after impact) and again in the terminal 88%\u0026ndash;100% window, with elite athletes showing less adduction and greater abduction than youth athletes. Increased support-hip abduction during retraction may reflect more active control of pelvic stability and lower-limb alignment, helping to dampen lateral sway and preserve a controllable base for landing and re-stabilisation \u003csup\u003e[31]\u003c/sup\u003e. The persistence of this abducted pattern late in the cycle likely represents continued stabilisation after foot return, potentially facilitating faster posture recovery and reduced centre-of-mass drift. Notably, the kicking limb displayed an opposite early-phase pattern (first 5%), with elite athletes showing greater adduction and less abduction, consistent with a \u0026ldquo;tightening\u0026rdquo; of the outgoing limb path before acceleration\u0026mdash;potentially limiting unnecessary lateral deviation at initiation and promoting a cleaner trajectory into the subsequent whip-like segmental acceleration \u003csup\u003e[32]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFor hip internal\u0026ndash;external rotation, the support limb exhibited multiple significant intervals spanning movement onset, the chamber-to-impact transition, and post-impact retraction, with elite athletes showing smaller internal rotation (i.e., a more externally rotated posture) overall. This suggests a more restrained trade-off between generating rotation and maintaining support-side stability: avoiding excessive hip internal rotation during phases that demand force transfer and direction change may help preserve controllable lower-limb alignment and pelvic posture, reducing the tendency to \u0026ldquo;shift\u0026rdquo; rotational demands distally toward the knee \u003csup\u003e[33,34]\u003c/sup\u003e. The kicking limb showed a similar reduction in internal rotation during early retraction, consistent with stronger rotational braking and quicker recovery into a stance that better supports continuous attack\u0026ndash;defence transitions. For youth athletes, these findings argue against focusing only on \u0026ldquo;kicking faster\u0026rdquo;, instead, support-side rotational control, braking during retraction, and terminal re-stabilisation should be trained as distinct capacities to avoid slow recovery, post-impact instability, and disrupted action chaining in competition \u003csup\u003e[35]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eAt the knee, the support-limb difference occurred at the end of the kick cycle (95\u0026ndash;100%), where elite athletes showed greater knee flexion than youth athletes. This end-phase increase in knee flexion likely reflects a more controlled landing\u0026ndash;stabilisation strategy, allowing elite performers to absorb impact, re-centre the body mass, and re-establish a combat-ready stance more efficiently \u003csup\u003e[36]\u003c/sup\u003e. In contrast, reduced terminal knee flexion in youth athletes may indicate a stiffer or less coordinated landing response, which could compromise post-kick stability and slow the transition into subsequent actions \u003csup\u003e[37]\u003c/sup\u003e, with potential implications for injury risk \u003csup\u003e[38]\u003c/sup\u003e. Consistent with this interpretation, prior work has reported associations between support-limb knee frontal-plane positioning and scoring-relevant performance indicators, suggesting that better mediolateral knee regulation contributes to a more stable base and effective striking \u003csup\u003e[39]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn the kicking limb, knee transverse-plane behaviour also differed at key moments. Elite athletes exhibited smaller knee internal\u0026ndash;external rotation values (i.e., reduced internal rotation under the present sign convention) during 2\u0026ndash;9%, 43\u0026ndash;47%, and 90\u0026ndash;100% of the kick cycle. These discrete windows correspond to early initiation, the mid-cycle transition around the striking window, and terminal landing/end-phase stabilisation, respectively. Collectively, this pattern suggests tighter transverse-plane control of the kicking knee when the limb is being organised for acceleration, redirected for recovery, and re-stabilised after the kick \u003csup\u003e[40]\u003c/sup\u003e. For youth athletes, relatively greater knee internal rotation during these windows may reflect a more distal \u0026ldquo;compensation\u0026rdquo; strategy when proximal rotational control is less stable, potentially contributing to greater path variability and less decisive recovery \u003csup\u003e[41]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFor ankle dorsiflexion\u0026ndash;plantarflexion, the support limb showed significant differences at 16\u0026ndash;22% and across a prolonged late-cycle interval (58\u0026ndash;100%), with elite athletes demonstrating a more plantarflexed posture (i.e., reduced dorsiflexion) than youth athletes. This may reflect a stiffer ankle\u0026ndash;foot platform during early set-up as well as a more controlled re-stabilisation strategy during retraction and landing/end-phase \u003csup\u003e[42]\u003c/sup\u003e, which could facilitate faster balance recovery and readiness for follow-up actions. The kicking limb showed a similar plantarflexion-dominant difference during 57\u0026ndash;93%, suggesting that elite athletes maintain a tighter foot posture through late recovery, potentially supporting a more compact return path and more consistent preparation for foot placement.\u003c/p\u003e\n\u003cp\u003eFinally, a brief early between-group difference was observed for kicking-limb ankle abduction\u0026ndash;adduction during 0\u0026ndash;8% of the kick cycle, with elite athletes showing smaller abduction\u0026ndash;adduction angle values than youth athletes. Given the present sign convention (negative = abduction; positive = adduction), this indicates an early-phase shift toward less adduction and/or a more abducted foot orientation in elite performers during initiation. Such an early foot-positioning strategy may help establish a consistent limb trajectory and facilitate a quicker transition into the subsequent chambering and striking actions\u0026nbsp;\u003csup\u003e[43]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe phase-specific nature of the between-group differences identified by 1D SPM suggests that technical development in youth athletes may benefit more from targeted, phase-driven interventions than from globally increasing joint-angle magnitudes\u0026nbsp;\u003csup\u003e[44]\u003c/sup\u003e. Across the kick cycle, elite athletes tended to adopt a more \u0026ldquo;platform-like\u0026rdquo; support strategy during key windows, characterised by a less flexed support hip around chambering/strike execution, phase-dependent frontal-plane hip control toward the end of the cycle, and ankle posture modulation that was most evident during late recovery and landing\u0026ndash;stabilisation. These patterns point to a movement solution that prioritises a stable proximal base for rotation and rapid distal repositioning, rather than relying on large preparatory excursions or late compensations. From a coaching perspective, three training emphases follow. First, support-side platform control should be trained explicitly: single-leg stance tasks with pelvic control constraints and real-time feedback can be integrated into kick drills to reduce collapse and improve alignment during the preparatory and striking windows. Second, youth athletes may benefit from compact initiation strategies, in which the early phase is coached to minimise unnecessary kicking-leg \u0026ldquo;over-lifting\u0026rdquo; and lateral detours, thereby improving concealment and shortening time-to-peak knee extension\u0026nbsp;\u003csup\u003e[45]\u003c/sup\u003e. Third, because several between-group differences clustered in the recovery and terminal portions of the cycle, rapid recoil and landing\u0026ndash;stabilisation should be treated as a technical skill in its own right (e.g., time-limited return-to-guard drills, coupled with a brief post-landing \u0026ldquo;freeze\u0026rdquo; criterion to enforce end-phase control). A common maladaptive habit in youth athletes is to hang the leg after the strike and re-land with visible sway, which delays the return to fighting stance and disrupts subsequent attack\u0026ndash;defence transitions. A practical corrective cue is \u0026ldquo;retract first, stabilise second\u0026rdquo;: immediate kicking-leg retraction after impact, followed by controlled re-establishment of support-side alignment before initiating the next action. A limitation is that the striking event was defined kinematically (E3: peak knee extension) and may not coincide exactly with the instant of foot\u0026ndash;target contact due to target compliance and individual technique. Therefore, interpretations referring to \u0026ldquo;impact\u0026rdquo; should be understood as occurring around the putative striking moment (around E3) rather than at a directly measured contact time. Future studies should incorporate an instrumented target or synchronised video based contact detection to identify contact timing directly.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOverall, 1D SPM demonstrated that expertise-related differences in the roundhouse kick were not global magnitude changes across the entire waveform, but were concentrated in discrete, task-critical windows surrounding strike execution and post-strike retraction\u0026ndash;landing stabilisation. Relative to youth athletes, elite performers exhibited a more \u0026ldquo;platform-like\u0026rdquo; support strategy, characterised by a less flexed and less internally rotated support hip during key moments of force production and directional change, together with phase-dependent frontal-plane control that favoured a more abducted support-hip posture during retraction and terminal stabilisation. In the kicking limb, elite athletes showed reduced transverse-plane knee rotation at key moments, consistent with tighter rotational control during initiation, recovery, and end-phase stabilisation. At the ankle, elite athletes showed a more plantarflexed posture in the support limb during 16\u0026ndash;22% and 58\u0026ndash;100% of the cycle, and in the kicking limb during 57\u0026ndash;93%, which may reflect a more rigid ankle\u0026ndash;foot configuration and a faster return to a stable fighting stance. A brief early difference was also observed at movement onset in kicking-ankle abduction\u0026ndash;adduction (0\u0026ndash;8%). Collectively, these findings suggest that technical advancement from youth to elite performance is reflected less in uniformly larger joint excursions and more in phase-specific organisation of stability, rotation, and braking across the kinetic chain. Practically, coaching interventions for youth athletes may be most effective when targeting these key windows\u0026mdash;training a stable support-side platform, controlling transverse-plane motion without \u0026ldquo;dumping\u0026rdquo; rotation to the knee, and improving kick recovery and landing re-stabilisation\u0026mdash;to enhance action continuity and competitive effectiveness.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eAuthor contributions: J.S. conceived the study. J.S. and L.Y. designed the experimental protocol. J.S. and X.L. recruited participants and collected motion-capture data. J.S. curated the dataset and performed signal processing. J.S.and X.L. implemented the analysis pipeline and performed statistical analyses. J.S., L.Y. and G.S. interpreted the findings. J.S. wrote the first draft. G.S. and P.W. edited and revised the manuscript. J.S. prepared the figures and tables. All authors reviewed and approved the final manuscript.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are not publicly available due to participant privacy and institutional data protection policies but are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEstevan, I. \u0026amp; Falco, C. Mechanical analysis of the roundhouse kick according to height and distance in taekwondo. \u003cem\u003eBiol. Sport\u003c/em\u003e \u003cstrong\u003e30\u003c/strong\u003e, 275\u0026ndash;279 (2013).\u003c/li\u003e\n\u003cli\u003eGavagan, C. J. \u0026amp; Sayers, M. G. L. 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Twenty-three elite and 23 youth athletes performed roundhouse kicks recorded with a 12-camera Vicon system (200 Hz). Support- and kicking-limb hip, knee, and ankle angles (Cardan XYZ) were filtered (zero-lag 4th-order Butterworth, 15 Hz), time-normalised to 0\u0026ndash;100% (101 points; four phases \u0026amp; five events), and compared using 1D-SPM independent t-tests (RFT, α\u0026thinsp;=\u0026thinsp;0.05). Differences were phase-specific. Hip: elites were more extended at support 25\u0026ndash;35% (p\u0026thinsp;=\u0026thinsp;0.008) and 40\u0026ndash;45% (p\u0026thinsp;=\u0026thinsp;0.040), and kicking 0\u0026ndash;14% (p\u0026thinsp;=\u0026thinsp;0.005); more support abduction at 40\u0026ndash;65% (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and 88\u0026ndash;100% (p\u0026thinsp;=\u0026thinsp;0.004), but more kicking adduction at 0\u0026ndash;3% (p\u0026thinsp;=\u0026thinsp;0.041); smaller hip internal rotation (support p\u0026thinsp;\u0026le;\u0026thinsp;0.007; kicking p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Knee: greater support flexion at 95\u0026ndash;100% (p\u0026thinsp;=\u0026thinsp;0.015) and smaller kicking internal rotation at 2\u0026ndash;9% (p\u0026thinsp;=\u0026thinsp;0.002), 43\u0026ndash;47% (p\u0026thinsp;=\u0026thinsp;0.003), and 90\u0026ndash;100% (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Ankle: elites were more plantarflexed at support 16\u0026ndash;22% (p\u0026thinsp;=\u0026thinsp;0.040) and 58\u0026ndash;100% (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and kicking 57\u0026ndash;93% (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01); kicking ankle abduction\u0026ndash;adduction differed at 0\u0026ndash;8% (p\u0026thinsp;=\u0026thinsp;0.008). Elites adopt a more stable support posture and tighter rotation and braking, enabling rapid re-stabilisation; these windows are actionable targets for youth technique training.\u003c/p\u003e","manuscriptTitle":"Phase-specific lower limb kinematic differences during Taekwondo roundhouse kicks between elite and youth athletes revealed by 1D statistical parametric mapping","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-22 14:29:31","doi":"10.21203/rs.3.rs-8535585/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"965bbb99-1cff-431f-8b3b-8444a6884bd9","owner":[],"postedDate":"January 22nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":61540658,"name":"Health sciences/Anatomy"},{"id":61540659,"name":"Health sciences/Health care"},{"id":61540660,"name":"Health sciences/Medical research"},{"id":61540661,"name":"Biological sciences/Physiology"}],"tags":[],"updatedAt":"2026-03-30T06:25:59+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-22 14:29:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8535585","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8535585","identity":"rs-8535585","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}