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This is an excerpt from Essentials of Strength Training and Conditioning (Chapter 21) by National Strength and Conditioning Association (NSCA), G. Gregory Haff, and N. Travis Triplett

 When designing aerobic endurance training programs, it is important to understand those factors that influence and play a significant role in successful aerobic endurance performance. This allows for the development of sound training programs while minimizing unnecessary training that may lead to counterproductive adaptations, fatigue, injury, or overtraining.

Essentials of Strength Training and Conditioning 5^th Edition

Maximal Aerobic Capacity

As the duration of the aerobic endurance event increases, so does the proportion of the total energy demand that must be met by aerobic metabolism. Therefore, high maximal aerobic capacity (V̇O2max) is necessary for success in aerobic endurance events.[87] A high correlation has been shown to exist between V̇O2max and performance in aerobic endurance events.[2, 3, 134, 87] Consequently, aerobic endurance training programs should be designed, in part, to improve V̇O2max. However, although a high V̇O2max is important for successful performance, other factors may be equally or even more important. These factors include a high lactate threshold, good exercise economy, high efficiency in using fat as a fuel source, and a high percentage of type I muscle fibres.

For well-trained aerobic endurance athletes, improving V̇O2max may benefit performance only up to a certain point, especially since these individuals typically already possess excellent aerobic capacity. Consequently, the ability to sustain higher velocities during competition and training may have a greater impact on performance than attempting to make marginal improvements in aerobic capacity. For this reason, many athletes use high-intensity interval training (HIIT). HIIT may contribute to performance in highly trained aerobic endurance athletes via improvements in peak power output, ventilatory threshold, hydrogen ion buffering, use of fat as a fuel source, and improved exercise economy.[76]

Lactate Threshold

In aerobic endurance events, the best competitor among athletes with similar V̇O2max values is typically the person who can sustain aerobic energy production at the highest percentage of his or her V̇O2max without accumulating large amounts of lactic acid in the muscle and blood. [74] Although numerous terms have been used to refer to this phenomenon, lactate threshold (LT) is the one most commonly employed in the literature. Lactate threshold is that speed of movement or percentage of V̇O2max at which a specific blood lactate concentration is observed (i.e., 4 mmol/L of blood) or the point at which blood lactate concentration begins to increase above resting levels.[136] Several studies have shown that an athlete’s LT appears to be a better indicator of his or her aerobic endurance performance than V̇O2max.[7, 113]

The maximal lactate steady state (MLSS) is another term that often appears in the aerobic endurance training literature. The MLSS is defined as the exercise intensity at which maximal lactate production is equal to maximal lactate clearance within the body.[14] MLSS is an indicator of the transition from heavy to severe exercise intensity.[70)] In other words, while lactate production increases at the onset of exercise in the heavy exercise intensity domain, it plateaus and can be maintained at a steady state at this elevated level. However, if exercise intensity increases further, now entering the severe domain, lactate increases continually until failure. Notably, MLSS is also synonymous with critical power (CP) and critical speed (CS) in this regard. The MLSS is considered by many to be a better indicator of aerobic endurance performance than either V̇O2max or the LT.[14] What is clear from this information is that aerobic endurance athletes must improve their LT and MLSS. This requires athletes to conduct some training at elevated levels of blood and muscle lactate to maximize training improvements in these areas.

A measure of the energy cost of activity at a given exercise velocity is referred to as exercise economy. Athletes with a high exercise economy expend less energy during exercise to maintain a given exercise velocity (e.g., running speed). Several investigators have suggested that exercise economy is an important factor in successful performance in running events, [71] with better performers also having a slightly shorter stride length and greater stride frequency compared to less successful performers.[106]

During cycling, exercise economy can be affected by body mass size, cycling velocity, and aerodynamic positioning.[7, 41, 42] For cyclists, an increase in body mass and cycling velocity as well as an inefficient body position generate greater wind resistance, resulting in a decrease in exercise economy.

It has been demonstrated that elite swimmers are much more economical than non-elite swimmers[6] and use less oxygen at any given swimming velocity. The most profound impact on exercise economy during swimming can be observed when swimming technique becomes more efficient. As improvements in stroke mechanics occur, energy demand for a given swimming velocity is reduced. [146] Training to improve exercise economy is critical for aerobic endurance athletes.

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