Muscle fatigue: the cellular aspects.

High-intensity contractile activity causes a rapid fall in peak tension or force, a reduced shortening velocity, decline in power, prolonged twitch duration, a sarcolemma action potential with a prolonged duration, reduced amplitude, and a conduction velocity that may result in conduction block. The calcium transient is characterized by a reduced amplitude and prolonged duration. What is the role of hydrogen in high-intensity exercise? It may affect E-C coupling but we do not think so. It definitely inhibits the rate of force development and calcium binding to TN-C. It also definitely inhibits the cross-bridge transition from the low to high force state. It inhibits velocity or the cross-bridge cycle rate and, therefore, decreases power and, importantly, prolongs the rate of calcium reuptake by inhibiting the sarcoplasmic reticulum calcium ATPase pump. Phosphate inhibits tension by reversing the cross-bridge transition from the low to the high force state, but it does not affect cycle rate; therefore, it does not have an effect on velocity. It may be involved in decreasing the free energy of ATP hydrolysis, which would provide less energy and, most importantly, play a role in inhibiting the sarcoplasmic reticulum calcium reuptake. Finally, what does all this mean to the athlete and how can fatigue be prevented? Basically, we do not have answers to these questions, but it is clear that the athlete is going to have to have a varied training program. If an athlete trains with one particular type of exercise, fatigue will result from other factors. Thus, a heterogeneous training program is essential. Diet is very important, and warm-up and fluid replacement are all factors that are going to be important in triggering peak performance.