The relationship between passive ankle joint stiffness and the stiffness of muscles, nerve, and tendon

The relationship between passive ankle joint stiffness and the stiffness of muscles, nerve, and tendon | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (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];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results The relationship between passive ankle joint stiffness and the stiffness of muscles, nerve, and tendon View ORCID Profile Hiyu Mukai , View ORCID Profile Jun Umehara , View ORCID Profile Junya Saeki , View ORCID Profile Ko Yanase , View ORCID Profile Zimin Wang , View ORCID Profile Hiroshige Tateuchi , View ORCID Profile Noriaki Ichihashi doi: https://doi.org/10.1101/2025.09.09.675058 Hiyu Mukai a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Hiyu Mukai Jun Umehara a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan b Faculty of Rehabilitation, Kansai Medical University , 18-89 Uyama-higashi, Hirakata, Osaka 573-1136, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Jun Umehara For correspondence: umehara.jyu{at}kmu.ac.jp Junya Saeki b Faculty of Rehabilitation, Kansai Medical University , 18-89 Uyama-higashi, Hirakata, Osaka 573-1136, Japan c Graduate School of Rehabilitation, Osaka Kawasaki Rehabilitation University , 158 Mizuma, Kaizuka, Osaka 597-0104, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Junya Saeki Ko Yanase a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan b Faculty of Rehabilitation, Kansai Medical University , 18-89 Uyama-higashi, Hirakata, Osaka 573-1136, Japan d Faculty of Health and Sports Science, Doshisha University , 1-3 Tatara-Miyakodani, Kyotanabe, Kyoto 610-0394, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Ko Yanase Zimin Wang a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Zimin Wang Hiroshige Tateuchi a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Hiroshige Tateuchi Noriaki Ichihashi a Human Health Sciences, Graduate School of Medicine, Kyoto University , 53 Shogoin-Kawahara-cho, Kyoto 606-8507, Japan b Faculty of Rehabilitation, Kansai Medical University , 18-89 Uyama-higashi, Hirakata, Osaka 573-1136, Japan Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Noriaki Ichihashi Abstract Full Text Info/History Metrics Preview PDF Abstract Passive joint stiffness reflects the stiffness of various soft tissues across a joint. However, no previous studies have investigated the relationship between passive joint stiffness and muscle, nerve, and tendon stiffness. This study aimed to clarify whether passive ankle joint stiffness is related to stiffness in the triceps surae muscles, tibial nerve, and Achilles tendon. Thirty-eight healthy adults participated in the study. The passive ankle joint stiffness (slope of angle–passive torque curve) and shear wave velocities, which indicate soft tissue stiffness, of the triceps surae muscles and tibial nerve were measured at 5° of ankle plantarflexion and 5°, 15°, and 25° of ankle dorsiflexion. The shear wave velocity of the Achilles tendon was measured only at 5° of plantarflexion. A multiple regression model (forced-entry method) was constructed at each angle, specifying the shear wave velocities as the independent variables and passive joint stiffness as the dependent variable. At 5° of plantarflexion, no shear wave velocities were significantly related to passive joint stiffness (all p ≥ 0.05). At 5° and 15° of dorsiflexion, only the shear wave velocities of the tibial nerve were significantly positively related to passive joint stiffness ( p = 0.024 and 0.008, respectively). At 25° of dorsiflexion, the shear wave velocities of the lateral gastrocnemius muscle and tibial nerve were significantly positively related to passive joint stiffness ( p = 0.002 and 0.001, respectively). It can be concluded that both triceps surae muscles stiffness and tibial nerve stiffness are related to passive ankle joint stiffness. 1. Introduction Joint flexibility is regarded as an important outcome in sports and rehabilitation settings. The maximum angle during passive movement is often used as an indicator of flexibility. However, this measure reflects not only the flexibility of the soft tissues surrounding the joint but also stretch tolerance ( Ingram et al., 2025 ; Weppler and Magnusson, 2010 ). Therefore, researchers have adopted passive joint stiffness, which is the slope of the angle–passive joint torque curve, as an indicator of joint flexibility ( Chesworth and Vandervoort, 1989 ; Riemann et al., 2001 ). Previous studies have reported that an increase in passive ankle joint stiffness was observed in patients with spastic hypertonia ( Chung et al., 2004 ) and diabetes mellitus ( Rao et al., 2006 ) and in patients after ankle cast removal ( Chesworth and Vandervoort, 1995 ). An increase in passive joint stiffness may lead to activity limitations such as difficulty walking and it is important to investigate the factors relevant to passive joint stiffness to develop effective approaches for reducing stiffness. Passive joint stiffness is considered to reflect the stiffness of various soft tissues across a joint ( Riemann et al., 2001 ; Takeuchi et al., 2023 ). Some previous studies have investigated the relationship between passive joint stiffness and muscle and tendon stiffness using shear wave elastography. The results indicate that in healthy young adults, passive joint stiffness is not related to medial gastrocnemius and soleus muscle stiffness at 0° of ankle dorsiflexion; however, it is significantly positively related to triceps surae muscles stiffness at 15° or 20° of ankle dorsiflexion ( Chino and Takahashi, 2016 , 2015 ; Hirata and Akagi, 2022 ). Chino and Takahashi (2015) noted no significant correlation between passive joint stiffness and Achilles tendon stiffness at 0° of ankle dorsiflexion. Although there may be correlations between the stiffness of each soft tissue, previous studies have not investigated whether the stiffness of each soft tissue is independently related to passive joint stiffness. Additionally, in recent studies, researchers have evaluated nerve stiffness by using shear wave elastography and reported a significant relationship between tibial nerve stiffness and the maximum angle of ankle dorsiflexion ( Kawanishi et al., 2022 ; Mukai et al., 2025 , preprint). However, the exact relationship between passive joint stiffness and tibial nerve stiffness remains unclear. Therefore, it is necessary to investigate whether stiffness in the triceps surae muscles, Achilles tendon, and tibial nerve are independently related to passive joint stiffness, considering the correlation among soft tissue stiffnesses. This study aimed to clarify whether triceps surae (medial and lateral gastrocnemius and soleus) muscles, Achilles tendon, and tibial nerve stiffness are independently related to passive ankle joint stiffness using shear wave elastography. Passive joint stiffness is considered to reflect the stiffness of various soft tissues around a joint ( Riemann et al., 2001 ; Takeuchi et al., 2023 ). Previous studies have reported no significant correlation between passive joint stiffness and the medial gastrocnemius and soleus muscles at slightly lengthened positions. In contrast, significant correlations have been observed at greatly lengthened positions ( Chino and Takahashi, 2016 ; Hirata and Akagi, 2022 ). We hypothesized that i) passive ankle joint stiffness is related to triceps surae muscles, Achilles tendon, and tibial nerve stiffness, and that ii) triceps surae muscles stiffness is related to passive ankle joint stiffness more strongly at greatly lengthened positions. 2. Methods 2.1. Participants Forty-three healthy adults with no pain or limitation in the range of motion in their ankle joint on the non-dominant side participated in this study (19 males and 24 females; age, 24.3 ± 2.9 years; height, 165.8 ± 7.7 cm; body mass, 59.3 ± 8.2 kg). When the non-dominant leg was defined as the leg opposite to the one used in kicking a ball, 4 right legs and 39 left legs were targeted. All participants were informed regarding the study procedure in advance and written consent for participation was obtained. This study complied with the Declaration of Helsinki and was approved by the Ethics Committee (approval day: March 26, 2024, approval number: C1652-2). 2.2. Experimental procedure This cross-sectional study investigated the relationship between passive ankle joint stiffness and the shear wave velocities of the medial and lateral gastrocnemius muscles, soleus muscle, tibial nerve, and Achilles tendon, which were considered to represent the stiffness of these soft tissues. To measure these values, the participants were laid in a prone position on the seat of dynamometer (BIODEX System 4, BIODEX, NY, USA), with the hip and knee joint in neutral positions, foot of non-dominant side fixed to the footplate, and foot and pelvis fixed by straps. Participants were asked to relax during measurement. The measurement of the shear wave velocities was followed by that of the passive joint torque, which was necessary to calculate the passive joint stiffness. 2.3. Measurement of shear wave velocities The shear wave velocities were measured using the shear wave elastography mode in an ultrasound system (Aixplorer v12.2, SuperSonic Imagine, Aix-en-Provence, France). A linear probe (2 to 10 MHz, SuperLinear SL10-2) and musculoskeletal preset (muscle mode) were used to measure the shear wave velocities of the triceps surae muscles and tibial nerve. Another linear probe (4 to 15 MHz, SuperLinear SL 15-4) and musculoskeletal preset (foot–ankle mode) were used to measure the shear wave velocity of the Achilles tendon. All measurements were performed with the following settings: mode, penetration; frequency, 1.7 Hz; smoothing level, five; persistence, high; opacity, 100%. We interpreted higher shear wave velocities as representing higher stiffness. The shear wave velocities were measured at the following regions: the medial and lateral gastrocnemius muscles at 30% of lower leg length ( Akagi and Takahashi, 2013 ; Nakamura et al., 2014 ; Taniguchi et al., 2015 ), soleus muscle at 50% of lower leg length ( Kubo et al., 2017 ), tibial nerve at the region near the medial malleolus (determined through a preliminary study), and Achilles tendon at 4 cm proximal to the insertion to the calcaneal tubercle ( Selcuk Can et al., 2022 ). To minimize the effect of stretching, the shear wave velocities were measured at 5° of ankle plantarflexion and 5°, 15°, and 25° of ankle dorsiflexion in order. The shear wave velocity of the Achilles tendon was measured only at 5° of ankle plantarflexion due to saturation. To analyze the ultrasound images, a rectangular region of interest 1 cm in height and 2 cm in width was defined. Then, using a Q-box trace function, the maximum area within the region of interest was encapsulated, excluding the bone, aponeurosis, or epineurium, and the mean of the shear wave velocities in the encapsulated region was calculated. Two images of each muscle and three images of the tibial nerve and Achilles tendon were acquired, and the mean values were used in our statistical analysis. The analyzed ultrasound images are presented in Figure 1 . Download figure Open in new tab Figure 1: Analyzed ultrasound images a: medial gastrocnemius muscle, b: lateral gastrocnemius muscle, c: soleus muscle, d: tibial nerve, and e: Achilles tendon. The rectangle in the ultrasound image is the region of interest. The area surrounded by white wavy lines is the target area of analysis. The area indicated by the yellow arrow is the target tissue for measurement. 2.4. Measurement and correction of passive joint torque and calculation of passive joint stiffness To measure the passive joint torque, each participant’s ankle was passively dorsiflexed by 5°/s from 30° of ankle plantarflexion to the maximum dorsiflexion angle, where the participant felt discomfort without pain ( Nakamura et al., 2017 ). Prior to the testing session, two sessions were conducted to familiarize the participants with the procedure ( Hirata et al., 2015 ; Konrad et al., 2015 ; Konrad and Tilp, 2014 ). Then, three testing sessions were conducted. To subtract the torque generated by the mass of foot from the measured passive joint torque, the gravitational force acting on the foot was calculated by dividing the measured passive joint torque at 30° of ankle plantarflexion by sine(30°). Because 30° of ankle plantarflexion is under slack angle for the triceps surae muscles ( Hirata et al., 2016 ), the measured passive joint torque at this angle can be interpreted as the torque generated by the mass of foot. The torque generated by the mass of foot at any angle of ankle plantarflexion/dorsiflexion was then calculated by multiplying the gravitational force acting on the foot by the sine of the angle. The passive joint torque was corrected by subtracting the torque generated by the mass of foot from the measured passive joint torque. The relationship between the angle and corrected passive joint torque was generated by fitting a fourth-order polynomial equation to the data ( y = ax 4 + bx 3 + cx 2 + dx + e , where y is the torque, x is the joint angle, and a to e are constants). The passive joint stiffness at 5° of ankle plantarflexion, and 5°, 15°, and 25° of ankle dorsiflexion was calculated using the first derivative (slope) of that equation ( Chesworth and Vandervoort, 1989 ; Riemann et al., 2001 ). The passive joint stiffness was calculated three times and the mean value was used for statistical analysis. 2.5. Statistical analysis SPSS Statistics 22 (IBM, Armonk, NY, USA) was used for statistical analysis. To confirm the normality of the data, the Shapiro–Wilk test was performed. As a primary analysis, to clarify the relationship between the soft tissue stiffness and passive joint stiffness, multiple regression analysis using the forced-entry method was performed, specifying the shear wave velocity of each soft tissue as the independent variable and passive joint stiffness as the dependent variable. A regression model was constructed at each angle for which the shear wave velocities and passive joint stiffness were calculated. As a sub-analysis, to clarify the correlation in the shear wave velocities among the soft tissues at 5°, 15°, and 25° of ankle dorsiflexion, Pearson’s product–moment correlation coefficients or Spearman’s rank correlation coefficients were calculated. Statistical significance for all results was defined as p < 0.05. 3. Results 3.1. Characteristics of participants After excluding four participants whose maximum ankle dorsiflexion angle was less than 25° and one participant who felt pain during the measurement of the shear wave velocities, 38 participants were included in the statistical analysis. The characteristics of the 38 participants included in the statistical analysis were as follows: 17 males and 21 females; age, 24.6 ± 2.8 years; height, 166.2 ± 7.6 cm; body mass, 60.1 ± 8.0 kg; 33 right-footed and 5 left-footed individuals. The passive joint stiffness and shear wave velocities at each angle are presented in Table 1 . View this table: View inline View popup Download powerpoint Table 1: Passive ankle joint stiffness and shear wave velocity of each tissue 3.2. Relationship between passive joint stiffness and shear wave velocity At 5° of ankle plantarflexion, no shear wave velocities of any soft tissues were significantly related to passive joint stiffness (all p ≥ 0.05). At 5° and 15° of ankle dorsiflexion, the shear wave velocities of the tibial nerve were significantly positively related to passive joint stiffness ( p = 0.024 and 0.008, respectively). However, the shear wave velocities of the triceps surae muscles were not significantly related to passive joint stiffness (all p ≥ 0.05). At 25° of ankle dorsiflexion, the shear wave velocities of the lateral gastrocnemius muscle and tibial nerve were significantly positively related to passive joint stiffness ( p = 0.002 and 0.001, respectively). The shear wave velocities of the medial gastrocnemius and soleus muscles were not significantly related to passive joint stiffness ( p = 0.185 and 0.394, respectively). The results of multiple regression analysis at each angle are presented in Table 2 . View this table: View inline View popup Download powerpoint Table 2: Results of multiple regression analysis 3.3. Correlation of shear wave velocities between each soft tissue At 5° of ankle dorsiflexion, the shear wave velocity of the lateral gastrocnemius muscle was significantly correlated with those of the medial gastrocnemius (ρ = 0.591, p < 0.001) and soleus muscles (ρ = 0.501, p = 0.001). At 15° of ankle dorsiflexion, the shear wave velocity of the medial gastrocnemius muscle was significantly correlated with those of the lateral gastrocnemius (r = 0.666, p < 0.001) and soleus muscles (ρ = 0.384, p = 0.017). Additionally, the shear wave velocity of the lateral gastrocnemius muscle was significantly correlated with those of the soleus muscle (ρ = 0.465, p = 0.003) and tibial nerve (r = 0.423, p = 0.008). At 25° of ankle dorsiflexion, the shear wave velocity of the medial gastrocnemius muscle was significantly correlated with that of the lateral gastrocnemius muscle (r = 0.426, p = 0.008). All results for the correlation of the shear wave velocities between each soft tissue are provided in Supplemental Material 1 . View this table: View inline View popup Download powerpoint Supplemental Material 1: Correlation of shear wave velocity between each tissue 4. Discussion In this study, we investigated the relationship between passive joint stiffness and the shear wave velocities of the triceps surae muscles, Achilles tendon, and tibial nerve. We found that the shear wave velocity of the tibial nerve was independently related to passive joint stiffness at 5°, 15°, and 25° of ankle dorsiflexion. At 25° of ankle dorsiflexion, the shear wave velocity of the lateral gastrocnemius muscle is also independently related to passive joint stiffness. Previous studies have reported significant relationships between maximum joint angle (an indicator of joint flexibility), and muscle ( Hirata et al., 2020 ; Miyamoto et al., 2018 ) and nerve stiffness ( Kawanishi et al., 2022 ; Mukai et al., 2025 , preprint). This is the first study to demonstrate that muscle and nerve stiffness are also related to passive joint stiffness. The positive relationship between passive joint stiffness and the shear wave velocity of the tibial nerve at 5°, 15°, and 25° of ankle dorsiflexion indicates that individuals with higher tibial nerve stiffness have higher joint stiffness. Although passive joint stiffness has been suggested to reflect the stiffness of not only muscles but also other soft tissues ( Riemann et al., 2001 ; Takeuchi et al., 2023 ), this assumption has not been clearly validated through empirical studies. It should be noted that a significant relationship with tibial nerve stiffness was observed at 5° and 15° of ankle dorsiflexion; however, the adjusted R 2 values were small (0.101 and 0.198, respectively). Therefore, passive joint stiffness cannot be explained by tibial nerve stiffness alone. Contradictory to our two hypotheses, excluding the lateral gastrocnemius muscle at 25° of ankle dorsiflexion, the shear wave velocities of the triceps surae muscles were not significantly related to passive joint stiffness. Chino and Takahashi (2015) reported no significant relationship between the shear modulus of the medial gastrocnemius muscle and passive joint stiffness at a slightly lengthened position, which is consistent with the results of this study. However, inconsistent with this study, previous studies have reported that the shear moduli of the triceps surae muscles were significantly positively related to passive joint stiffness ( Chino and Takahashi, 2016 ; Hirata and Akagi, 2022 ). Koo and Hug (2015) proposed the following equation: where G is the muscle shear modulus at any length, F is the muscle passive force at the length along its long axis, G 0 is the muscle shear modulus at its slack length, and s is the slope of the F–G relationship. In this study, individual differences may have existed in G 0 and the relative proportion of each muscle comprising the triceps surae muscles in F . Considering such individual differences, triceps surae muscles stiffness may not be related to passive joint stiffness, excluding the lateral gastrocnemius muscle at 25° of ankle dorsiflexion. As a result of multiple regression analysis, no significant relationship was observed between passive joint stiffness and the shear wave velocity of the lateral gastrocnemius muscle at 15° of ankle dorsiflexion ( Table 2 ). However, correlation analysis revealed that passive joint stiffness tended to be positively correlated with the shear wave velocity of the lateral gastrocnemius muscle at 15° of ankle dorsiflexion (r = 0.314, p = 0.055) ( Supplemental Material 2 ). At this angle, a significant correlation was observed between the shear wave velocities of the lateral gastrocnemius muscle and that of the tibial nerve (r = 0.423, p = 0.008) ( Supplemental Material 1 ). These results suggest the necessity for considering the correlations among the stiffness of each soft tissue to investigate the relationship between passive joint stiffness and the stiffness of various soft tissues. Hirata and Akagi (2022) investigated the relationship between triceps surae (medial and lateral gastrocnemius and soleus) muscles stiffness and passive ankle joint stiffness. However, they did not perform statistical analysis considering the correlations among the stiffness values of each muscle. Although the physiological or biomechanical mechanisms associated with the correlation among the stiffness values of each soft tissue remain unclear, the consideration of correlation may provide more meaningful knowledge when investigating the relationship between passive joint stiffness and the stiffness of various soft tissues. View this table: View inline View popup Download powerpoint Supplemental material 2: Correlation between passive joint stiffness and shear wave velocities at 5°, 15°, and 25° of ankle dorsiflexion At 5° of ankle plantarflexion, no significant relationship was observed between passive joint stiffness and Achilles tendon stiffness. However, the passive joint stiffness at this angle was minimal ( Table 1 ) and the Achilles tendon may not have been sufficiently elongated. In this study, we could not measure the shear wave velocity of the Achilles tendon in ankle dorsiflexion due to saturation. Therefore, we cannot say definitively that Achilles tendon stiffness is not related to passive ankle joint stiffness. There are two limitations of this study. First, we did not evaluate the stiffness of soft tissues other than the triceps surae muscles and tibial nerve, such as other plantarflexors, aponeurosis, skin, blood vessels, or subcutaneous fat. Because passive joint stiffness reflects the stiffness of various soft tissues across the joint, soft tissues which were not evaluated in this study may be related to passive joint stiffness. Second, we evaluated only at the position with 0° of hip and knee flexion. Previous studies have reported that the shear wave velocities of the triceps surae muscles and tibial nerve varied depending on the angles of hip or knee flexion, even at the same angle of ankle dorsiflexion ( Andrade et al., 2022 ; Ateş et al., 2018 ; Le Sant et al., 2017 ). For hip or knee flexion angles different from that considered in this study, different results may be observed in the relationship between passive joint stiffness and soft tissues stiffness. In future studies, it will be necessary to investigate these relationships by considering additional soft tissues and positions. 5. Conclusion We investigated the relationship between passive ankle joint stiffness and soft tissue (triceps surae muscles, tibial nerve, and Achilles tendon) stiffness using shear wave elastography. At 5° and 15° of ankle dorsiflexion, only the shear wave velocities of the tibial nerve were significantly related to passive joint stiffness. At 25° of ankle dorsiflexion, the shear wave velocities of the lateral gastrocnemius muscle and tibial nerve were significantly related to passive joint stiffness. This results of this study suggest that passive joint stiffness reflects the stiffness of not only muscle but also nerves. CRediT authorship contribution statement Hiyu Mukai: Writing – original draft, Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization. Jun Umehara: Conceptualization, Methodology, Writing – review, Editing. Junya Saeki: Conceptualization, Methodology, Writing – review, Editing. Ko Yanase: Conceptualization, Methodology, Writing – review, Editing. Zimin Wang: Conceptualization, Methodology, Writing – review, Editing. Hiroshige Tateuchi: Conceptualization, Methodology, Writing – review, Editing. Noriaki Ichihashi: Conceptualization, Methodology, Writing – review, Editing. Project administration and Supervision. Data statement The datasets generated during and/or analyzed during this current study are available from the corresponding author upon reasonable request. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper. Funding This work was supported by JST SPRING (grant number JPMJSP2110). Acknowledgement We are grateful to Editage ( www.editage.jp ) for their assistance with English language editing. Funder Information Declared JST SPRING , JPMJSP2110 Footnotes E-mail address Hiyu Mukai: hiyu4035{at}gmail.com Junya Saeki: saekij{at}kawasakigakuen.ac.jp Ko Yanase: kyanase{at}mail.doshisha.ac.jp Zimin Wang: wangzimin1995{at}gmail.com Hiroshige Tateuchi: tateuchi.hiroshige.8x{at}kyoto-u.ac.jp Noriaki Ichihashi: ichihashi.noriaki.5z{at}kyoto-u.ac.jp References ↵ Akagi , R. , Takahashi , H. , 2013 . Acute effect of static stretching on hardness of the gastrocnemius muscle . Med Sci Sports Exerc 45 , 1348 – 1354 . doi: 10.1249/MSS.0b013e3182850e17 OpenUrl CrossRef ↵ Andrade , R.J. , Freitas , S.R. , Hug , F. , Coppieters , M.W. , Sierra-Silvestre , E. , Nordez , A. , 2022 . Spatial variation in mechanical properties along the sciatic and tibial nerves: An ultrasound shear wave elastography study . 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Share The relationship between passive ankle joint stiffness and the stiffness of muscles, nerve, and tendon Hiyu Mukai , Jun Umehara , Junya Saeki , Ko Yanase , Zimin Wang , Hiroshige Tateuchi , Noriaki Ichihashi bioRxiv 2025.09.09.675058; doi: https://doi.org/10.1101/2025.09.09.675058 Share This Article: Copy Citation Tools The relationship between passive ankle joint stiffness and the stiffness of muscles, nerve, and tendon Hiyu Mukai , Jun Umehara , Junya Saeki , Ko Yanase , Zimin Wang , Hiroshige Tateuchi , Noriaki Ichihashi bioRxiv 2025.09.09.675058; doi: https://doi.org/10.1101/2025.09.09.675058 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Area Biophysics Subject Areas All Articles Animal Behavior and Cognition (7633) Biochemistry (17681) Bioengineering (13890) Bioinformatics (41929) Biophysics (21446) Cancer Biology (18586) Cell Biology (25492) Clinical Trials (138) Developmental Biology (13374) Ecology (19897) Epidemiology (2067) Evolutionary Biology (24308) Genetics (15606) Genomics (22497) Immunology (17736) Microbiology (40385) Molecular Biology (17175) Neuroscience (88584) Paleontology (666) Pathology (2831) Pharmacology and Toxicology (4822) Physiology (7641) Plant Biology (15149) Scientific Communication and Education (2045) Synthetic Biology (4293) Systems Biology (9822) Zoology (2271)