Endurance training

"Endurance training refers to prolonged, sustained exercise that's almost entirely aerobic. By relying on oxygen use for energy, low- to medium-intensity aerobic exercise can be kept up for long periods-hence the name "endurance." There isn't an exact upper limit on how long humans can endure exercise. Eventually, fatigue will set in, depending on intensity, fitness level, access to fuel, and willpower"--Provided by publisher.