Comparative analysis of consistency of adaptations to interval interventions individualized using sport-specific techniques in well-trained soccer players.

This study aimed to investigate the uniformity of adaptive changes in cardiorespiratory fitness and anaerobic power to high-intensity interval interventions (HIIT) designed using techniques specified for soccer players. Thirty well-trained athletes (age = 25 ± 3.1 years; body mass = 82.4 ± 3.4 kg; height = 183 ± 2.1 cm) were randomly assigned to two experimental groups engaging in interval intervention individualized using 30-15 Intermittent Fitness Test [HIITv_IFT (two sets of 5-8 min intervals, comprising 15 s of running at 95% of V_IFT followed by 15 s of passive recovery)], and small-sided game with matched timing (SSG [4 sets of 2.5-4 min 3 v 3 efforts]), as well as an active control group. Before and after a 6-week intervention consisting of three sessions per week, participants underwent a lab-based cardiorespiratory fitness test using breath-by-breath gas analyzer and non-invasive impedance cardiography to evaluate aerobic fitness and cardiac function measures. Also, anaerobic power was measured using lower-body Wingate test. Both interventions resulted in significant enhancement in all measures of cardiorespiratory fitness and anaerobic power over the training period. Analyzing inter-individual variability through determining residuals in individual changes indicated HIITv_IFT results in residuals in individual changes in ventilatory threshold (VT [first (VT₁) and second (VT₂)]), and peak and average power output than SSG (p = 0.02, 0.04, 0.02, and 0.01, respectively). In addition, the change in maximum oxygen uptake, maximal ventilation, and average power output following HIITv_IFT was notably greater than SSG (p = 0.002, 0.006, and, 0.019, respectively). There was no significant difference between HIITv_IFT and SSG in cardiac hemodynamics (cardiac output and stroke volume). Overall, by facilitating more homogenous stress, HIITv_IFT results in more identical physiological demands and more uniform adaptations in ventilatory threshold and anaerobic power than SSG.