Skeletal muscle metabolic and ionic adaptations during intense exercise following sprint training in humans

The effects of sprint training on muscle metabolism and ion regulation during intense exercise remain controversial. We employed a rigorous methodological approach, contrasting these responses during exercise to exhaustion and during identical work before and after training. Seven untrained men undertook 7 wk of sprint training. Subjects cycled to exhaustion at 130% pretraining peak oxygen uptake before (PreExh) and after training (PostExh), as well as performing another posttraining test identical to PreExh (PostMatch). Biopsies were taken at rest and immediately postexercise. After training in PostMatch, muscle and plasma lactate (Lac(-)) and H+ concentrations, anaerobic ATP production rate, glycogen and ATP degradation, IMP accumulation, and peak plasma K+ and norepinephrine concentrations were reduced (P < 0.05). In PostExh, time to exhaustion was 21% greater than PreExh (P < 0.001); however, muscle Lac(-) accumulation was unchanged; muscle H+ concentration, ATP degradation, IMP accumulation, and anaerobic ATP production rate were reduced; and plasma Lac(-), norepinephrine, and H+ concentrations were higher (P < 0.05). Sprint training resulted in reduced anaerobic ATP generation during intense exercise, suggesting that aerobic metabolism was enhanced, which may allow increased time to fatigue.