Energy system contribution to exercise….not what you think


Recent research in the past 10 years has indicated that the contribution to activities of short to moderate duration is not what was once thought. Exercise physiology books from the past 20 years (and even many still published today) suggest that the ATP-PC energy system was the overwhelmingly dominant energy source for activities through 6-10 seconds and that activities remained primarily anaerobic through as long as 4 minutes. Unfortunately, these guidelines, while useful at the time, were based on calculations of anaerobic energy release that drastically overestimated there contribution to activity. But as these findings were distributed repeatedly in textbooks and cited in papers over the next 10-15 years, many continue to believe the findings despite newer research to the contrary. As might be expected, this has created a host of misconceptions. The biggest one is that the energy systems contribute to ATP re-synthesis in a sequential manner (ATP-PC then Anaerobic Glycolytic then Aerobic) rather than an overlapping contribution where all attempt to contribute from the get-go. As a result, it was thought that the aerobic energy system did not play a significant role in performance outcomes of shorter duration activities when in reality, the aerobic energy system does play a role even in the shortest of activities and plays a significantly greater role at longer duration activities than was once thought. From a practical and training standpoint, this has little bearing for the extremes of the athletic world. Marathoners are still overwhelmingly aerobic and need to train as such. And there’s still no need for our short-duration, high-intensity athletes like baseball players or the speed-power events of track and field (throwing and jumping events, short sprints / hurdles) to be putting on ruffled ankle socks, a leotard and pulling out the Jane Fonda aerobics DVD. But there are some important implications for training in the gray area…for our intermediate duration, medium / high-intensity athletes (long sprinters and middle distance runners) and intermittent high-intensity athletes (like soccer and rugby)…it means we need rethink how we’re developing their aerobic energy system to meet the demands of their sport or activity and continue to fuel them for either sustained high intensity or repeated short bouts of high intensity.