Elite level endurance performance requires an athlete to have a large (>70 ml/kg/min) aerobic engine (VO2max) of which a high percentage (75-90%) of that maximal value can be maintained for upwards of 2 hours. This combination is augmented further by the ability to translate the chemical energy produced from oxygen to locomotion. Termed, exercise economy/efficiency, this physiologic characteristic describes the bodies’ ability to translate chemical energy, from the breakdown of ATP to mechanical energy (i.e. locomotion). When athletes of similar VO2max and threshold values compete, the winner is typically the one with the best efficiency/economy. While there are many benefits to thrifty exercise efficiency, one main benefit of higher efficiency/economy values is that the athlete with the higher values is less reliant on carbohydrate metabolism, thus sparing this finite resource during the same intensity of exercise. While it’s evident that exercise efficiency is a prerequisite to high-level endurance performance, the physiological determinants and trainability of these values poorly understood.
Physiologic Determinants of Efficiency/Economy.
Exercise efficiency/economy can vary between 30-40% in runners and 10-20% in cyclists, where at least 50% of this variance can be explained by the type I fiber distribution in cyclists, Joyner and Coyle (2008) speculate that the benefit of higher type one fibers is not for total oxidative capacity but for metabolic efficiency (changes in P/O ratio) which may or may not change over many years of training. As running is a more complex, weight-bearing exercise, the determinants of high level running economy still remain somewhat of a mystery, but it can be assumed that all components involved with contraction and support of skeletal muscle play an important role in the determination of efficiency.