Therefore, other metabolic pathways must be activated (Box 1), including substrate-level phosphorylation (or anaerobic) and oxidative phosphorylation (or aerobic). During submaximal exercise at ~200 W (~75% VO 2 max), the corresponding values are 0.4 mmol ATP kg −1 s −1 and ~15 s, respectively. For example, during all-out, maximal exercise (such as sprinting) at a power output of 900 W (~300% maximal oxygen uptake (VO 2 max)), the estimated rate of ATP utilization is 3.7 mmol ATP kg −1 s −1, and exercise could last <2 s if stored ATP were the sole energy source. Because the intramuscular stores of ATP are relatively small (~5 mmol per kg wet muscle), they are unable to sustain contractile activity for extended periods. The availability of ATP is critical for skeletal muscle contractile activity, both in explosive-power or sprint events lasting for seconds or minutes and in endurance events lasting for hours.ĪTP is required for the activity of key enzymes involved in membrane excitability (Na +/K + ATPase), sarcoplasmic reticulum calcium handling (Ca 2+ ATPase) and myofilament cross-bridge cycling (myosin ATPase). Such efforts are a culmination of years of dedicated training, and athletic performance is determined by a complex interaction of biological, mental and environmental factors. Perhaps we may wonder how these feats are achieved. When the Olympics takes place, we will witness extraordinary physical and mental efforts in track and field, water and air. In 2020, athletes from around the world were to gather in Tokyo for the quadrennial Olympic festival of sport, but the event has been delayed until 2021 because of the COVID-19 pandemic. We also summarize various interventions that target muscle metabolism for ergogenic benefit in athletic events. Here, we provide an overview of exercise metabolism and the key regulatory mechanisms ensuring that ATP resynthesis is closely matched to the ATP demand of exercise. ![]() For most events at the Olympics, carbohydrate is the primary fuel for anaerobic and aerobic metabolism. ![]() The relative contribution of these metabolic pathways is primarily determined by the intensity and duration of exercise. These pathways include phosphocreatine and muscle glycogen breakdown, thus enabling substrate-level phosphorylation (‘anaerobic’) and oxidative phosphorylation by using reducing equivalents from carbohydrate and fat metabolism (‘aerobic’). Because the muscle stores of ATP are small, metabolic pathways must be activated to maintain the required rates of ATP resynthesis. The continual supply of ATP to the fundamental cellular processes that underpin skeletal muscle contraction during exercise is essential for sports performance in events lasting seconds to several hours.
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