Abstract
This study compared inter-individual variability in the adaptive responses of cardiorespiratory fitness, anaerobic power, and motor abilities of male volleyball players to high-intensity interval training (HIIT) prescribed as repetitive drop jumps (interval jumping) and running-based intervals (interval running). Twenty-four collegiate volleyball players were equally randomized to two training groups executing 11 minutes of interval running or interval jumping during which they ran or repeated drop-jumps for 15 seconds, alternating with 15 seconds of passive recovery. Before and after the 6-week training period, aerobic fitness, cardiac function, and anaerobic power were evaluated using a graded exercise test, impedance cardiography, and a lower-body Wingate test, respectively. Additionally, linear speed, agility, and jumping tests determined motor abilities. Both interventions significantly enhanced maximum oxygen uptake (V̇O(2max)), velocity associated with V̇O(2max), first and second ventilatory thresholds (VT(1) & VT(2)), maximal cardiac output (Q̇(max)), stroke volume (SV(max)), peak and average power output, vertical jump, change of direction, and linear sprint speed. Interval jumping group demonstrated a significantly greater improvement in squat jump (p = 0.001; 95% CI: 2.51-5.42) and countermovement jump (p = 0.001; 95% CI: 2.11-4.61) compared to interval running group. Conversely, interval running group elicited a greater enhancement in sprint speed (p = 0.002; 95% CI: 2.53-5.71) than interval jumping group. Examining the individual residual in the adaptive responses revealed that interval running induced more homogenized adaptations across individuals in VT(1) (p = 0.04; 95% CI: 0.03-1.33), Q̇(max) (p = 0.03; 95% CI: 0.04-1.64), SV(max) (p = 0.04; 95% CI: 0.02-1.75), and maximal sprint speed (p = 0.01; 95% CI: 0.72-1.95) in contrast to interval jumping. However, the uniformity of adaptations in countermovement jump in response to interval jumping surpassed that of interval running (p = 0.02; 95% CI: 0.08-1.32). Although both training modalities effectively improved the mentioned variables concurrently, tailoring the HIIT intervention to the reference intensity and training modality specific for each quality may enhance measured quality.