Inter-individual variations in hormonal, physiological, and performance adaptations to various forms of high-intensity interval interventions in collegiate soccer players

This study compared the inter-individual variability in adaptive responses of hormonal, physiological, and physical performance measures to various forms of high-intensity interval interventions in collegiate soccer players. Forty male players participated in this study and were randomly assigned to traditional running-based sprint interval training (SIT), small-sided games (SSGs), short sprint interval training (SSIT), and a control group (CON), each of 10. Before and after training period, hormonal (testosterone and cortisol), physiological (maximum oxygen uptake [V̇O 2max ], V̇O 2 /HR, first and second ventilatory threshold [VT 1 and VT 2 ], peak and average power output [PPO and APO]), and performance (Yo-Yo IR1, countermovement vertical jump, 20-m sprint, L-run, and maximal kicking distance [MKD]) variables were measured. Analyzing individual responses revealed significantly greater adaptive responses of Yo-Yo IR1, VT 2 , and cortisol levels (p < 0.05), as well as lower residuals in changes in Yo-Yo IR1, VO 2max , VT 1 and VT 2 , and PPO to SSIT compared to SIT and SSGs (p < 0.05). By contrast, the SSGs group resulted in greater adaptations (p = 0.002) in MKD than the SIT and SSIT. By diminishing inter-individual variability in adaptive responses, SSIT results in more homogenous adaptations in measures of cardiorespiratory fitness, hormonal adaptations and sport-specific performance than SIT and SSGs.