Amino-Acid and Recovery Responses Across Two Fixed-Sequence HIIT Sessions in Trained Male Football Players

This study evaluated how trained young male football players responded to two high-intensity interval training (HIIT) sessions that differed in the length of the passive recovery period between repeated running bouts. Participants completed both exercise conditions in a fixed order. The first session used 10 seconds of high-intensity running followed by 10 seconds of passive recovery (HIIT 1:1). Seven days later, the same participants completed a second session using 10 seconds of high-intensity running followed by 20 seconds of passive recovery (HIIT 1:2). Both exercise sessions were matched for exercise intensity, active work duration, number of repetitions, and prescribed running distance. Participants were assessed before exercise, immediately after exercise, and at 6, 24, 48, and 72 hours after each session. The study examined biochemical responses, perceived muscle soreness, countermovement jump performance, and changes in circulating amino acids and amino acid-related compounds. The purpose was to describe and compare recovery responses across the two fixed-sequence HIIT sessions. Because all participants completed HIIT 1:1 first and HIIT 1:2 second, the study was not randomized or counterbalanced, and any differences between sessions may also reflect session-order effects.