On Your Mark, Get Set, Choose! A Randomized Cross-Over Study Comparing Fixed and Self-Selected Rest Periods in Interval Running Among Professional Female Soccer Players.

Abstract Background Studies on rest durations during high-intensity interval training (HIIT) often compare fixed and self-selected (SS) rest allocation approaches. Frequently, the rest duration under SS conditions is unlimited, leading to inconsistent total rest durations compared to fixed rest conditions. To address this limitation, we recently compared fixed and SS rest conditions during cycling HIIT sessions, while keeping the total rest time equivalent. However, our protocol required athletes to divide a long total rest time (12 minutes) across nine intervals, which may have been overly cognitively demanding. In the current study, we simplified the athletes’ rest allocation task by reducing the number of rest periods available. Methods Following a familiarization session, 24 professional female soccer players completed two running HIIT sessions on a non-motorized treadmill. Each session consisted of twelve 15-second intervals, divided into three blocks, with the goal of maximizing the distance covered. In both conditions, the between-interval rest duration per block amounted to 270 seconds. In the fixed condition, the rest was uniformly allocated to 90 seconds between each interval, whereas in the SS condition, the athletes chose how to allocate the entirety of the 270 seconds of rest. We compared the following outcomes: distance, heart-rate, perception of fatigue, effort, autonomy, enjoyment, boredom, and athletes’ preferences. Outcomes were compared using aggregated measures via paired univariate tests, and across the intervals via mixed-effects models. Results We observed comparable results in most outcomes with the exception of higher autonomy in the SS condition (mean difference = 2.1, 95%CI (0.9, 3.3)) and a negligibly higher heart-rate when comparing the observations across intervals (estimate = 2.5, 95%CI (0.9, 4.2)). Additionally, participants chose to rest for longer durations as the block progressed. Finally, most participants (65%) favored the SS condition. Conclusion This study further solidifies that SS and fixed approaches with matched total rest durations result in similar performance, physiological, and psychological responses. This effect persists even when the total rest duration required to be allocated is relatively short. Therefore, coaches and trainees can choose either approach based on their preferences and training goals.