Muscle Metabolism and Performance During Simulated Peak-Intensity Periods Occurring Early and Late in a Soccer-Specific Exercise Protocol in Well-Trained Male Players.

We applied a novel model mimicking the most intense 5-min game periods to investigate muscle metabolic and fatigue responses to peak-intensity exercise occurring early and late in a simulated soccer game. Eleven well-trained male players completed a modified simulated soccer game (the Copenhagen Soccer Test) with 5-min peak-intensity period simulations inserted early (PP1; 10-15 min) and late (PP2; 85-90 min) in the game. Muscle biopsies and blood samples were obtained before and after each peak period. Muscle glycogen decreased during both peak periods (p < 0.001) by 62 ± 46 mmol kg-1 dw in PP1 and by 25 ± 37 mmol kg-1 dw in PP2, without a statistically significant difference in the glycogen breakdown in PP1 vs. PP2, despite a numerical trend (p = 0.115). Muscle lactate increased during both peak periods (p < 0.001) to 47 ± 25 mmol kg-1 dw and 32 ± 12 mmol kg-1 dw, with no clear difference in the increase (p = 0.108), despite blood lactate levels rising more in PP1 vs. PP2 (p = 0.031), reaching higher post PP1 levels (13.9 ± 3.6 mmol L-1 vs. 9.8 ± 2.4 mmol L-1, p = 0.003). Muscle ATP decreased by 4% (p = 0.004) and phosphocreatine by ~50% (p < 0.001) following both peak periods. RPE was higher during PP2 (10.0 ± 0.0 AU vs. 9.2 ± 0.8 AU, p = 0.023), while 10-m sprint performance declined by ~10% (p < 0.001), with no differences between PP1 and PP2 (p = 0.280). In conclusion, a 5-min peak period occurring early in a simulated game elicited a high anaerobic energy turnover, with marked muscle glycogen reductions, lactate accumulation, and PCr depletion. While high-energy phosphate metabolism remained similar during the late peak period, glycogenolytic rate appeared attenuated, accompanied by aggravated perceived exertion but similar sprint performance deteriorations.