I was asked in a recent assignment to discuss a sport athlete that utilizes all three of the major energy pathways. I would like to address the idea that no sport relies completely on one system. This is an important point and implies (correctly) that all three energy systems are functioning at all times to varying degrees; they do not simply turn on and off like a light switch. But it is easiest for us to think about them in terms of which is the major energy producer at any given time with respect to intensity and duration. Although distance runners are generally thought to use primarily the oxidative pathway, they use all three pathways quite a bit more than most people think. Particularly mountain trail runners, which will be the focus of this short explanation.
Mountain trail running is a flavor of distance running that involves long distances, steep climbs and descents, and often technical terrain and obstacles to negotiate. The lion’s share of a mountain runner’s time is spent in the aerobic zone, burning fatty acid stores for a seemingly endless supply of energy. But when the going gets steep, the intensity ramps up rapidly (as pace decreases). It is not uncommon for mountain runners to spend up to 20-30 minutes running uphill. During these climbs, the non-oxidative (glycolytic) energy pathway is initially called upon to provide energy to the muscles, but after approximately two minutes this pathway is unable to meet the demanded energy needs, forcing the body to rely on the oxidative pathway. As a consequence, intensity and corresponding performance output decrease notably. The immediate (ATP-CP) energy pathway is also utilized in mountain running, particularly on technical trails with ankle-breaking roots, rocks, fallen trees, or uneven terrain. On these sections, runners often perform sudden and highly intense movements to continue down the trail; on these occasions the ATP-CP pathway is called upon to provide that immediate ATP energy source to meet imposed demands.
The point of this short explanation was to show that although we typically break up the energy pathways into three separate entities, they all three share the burden of producing energy in our bodies, each taking the lead role when its assigned set of conditions are met with respect to intensity, duration, and environment.