Christensen, E. H. (1962). Speed of work. Ergonomics, 5, 7-13.

A large amount of research in exercise physiology has focused on aerobic endurance. Much less has emphasized heavy or moderately heavy work. Every increase in workload demands more oxygen, which in turn increases the load on respiration, circulation, and heat regulation. Training athletes by having them experience very high physiological stress for "long" periods, limits eventual adaptation and produces fatigue of sufficiently high levels and lasting effects that subsequent training is disrupted. Such work actually reduces the amount of effective training rather than being an effective way of improving ultimate performance.

The major confounding factor with prescribing training loads is individual variations in work capacity. While norms and tables that indicate ranges are produced, they do not satisfy any need for individual exercise prescription. Most of all, such general guidelines do not accommodate individual variations in how effort is distributed most efficiently over a long bout of heavy work.

A great quantity of heavy muscular work can be performed if it is performed as many short work and rest periods. This produces a submaximal load on circulation and respiration and allows training volume to be significantly greater than if work is performed for longer periods. Respiratory and circulatory stress and lactate accumulation, features of debilitating training fatigue for athletes, are avoided with ultra-short training.

The reason ultra-short training works on developing aerobic endurance is that it taxes endurance development in the periphery (in the muscles). It uses as its primary oxygen source, oxygen stored in the muscles and circulating in the blood. Over and over again, these oxygen sources are depleted and replenished causing these mechanisms of oxygen delivery to be stimulated maximally. They are stimulated much more in ultra-short training than in continuous work (where the intensity of work is lower and/or non-specific). Ultra-short work appears to be the only way maximal stimulation of this important feature of aerobic adaptation occurs, possibly because of the volume of exercise accomplished. The added factor of this adaptation occurring with neuromuscularly correct exercises is one more justification for its use. Ultra-short training is the best way of stimulating aerobic adaptation in the periphery while not overtaxing the central mechanisms (respiration, circulation, heat generation) of aerobic work.

High-effort-level sporting event-specific training can be performed using very short work bursts and brief rests. Not only is the total volume of work increased, but so is the volume of specific high-intensity work-quality maintained. Neuromuscular patterning of a competition-specific nature can be enhanced.

This work puts to rest the claim that sport training, which produces high levels of fatigue with high levels of lactate, is a "good" training experience. Such training is often called "lactate tolerance" training. It reduces the volume and quality of potentially beneficial training that could be performed, and therefore, should be viewed as detrimental to possible adaptation, certainly when compared to what can be achieved with ultra-short training.

Implication. Ultra-short training, rather than lactate-tolerance training, is the better method for developing performance improvements in heavy work or high intensity sporting events.

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