Astrand, I., Astrand, P-O., Christensen, E. H., & Hedman, R. (1960). Intermittent muscular work. Acta Physiologica Scandinavica, 48, 448-453.

A well-conditioned male performed several one-hour bouts of cycle ergometry producing a constant work output of 64,800 kpm. Each exercise consisted of alternating work and rests of .5, 1, 2, or 3 minutes. Continuous work for one hour at half-the intensity was also performed.

It was found that the heavy work was transformed into a submaximal load on respiration and circulation with the shorter work periods of .5 and 1 minute.

Mechanical efficiency was highest in the easier continuous work. Among the intermittent experiences, the shorter time periods, and in particular the .5 minute work/rest alternation, yielded the highest efficiency. As the interval of intermittent work increased, mechanical efficiency decreased.

Work with the short periods (.5 and 1 minute) was perceived to be relatively light, and no significant fatigue was experienced in the one-hour. Work at two, and especially three minutes, produced an exhausting maximal load.

The most surprising result was the low lactate values at the .5 minute work, less than half that achieved with 1-minute work, and much less than at the remaining two longer work periods.

The significant implication of this study was that a great amount of heavy work can be performed with a submaximal load on circulation and respiration by a suitable application of short work and rest periods. Large muscle groups can be trained without simultaneously loading the respiratory and circulatory organs. The term for this form of training is "ultra-short training."

Thus, it is possible to effectively train full-effort, large-muscle activities while enjoying circulatory and respiratory (aerobic) training effects similar to those achieved with continuous activities performed at a much lower level of intensity. This should be a superior form of training to more established, but less beneficial, forms that still pervade most sports. This investigation showed clearly, that hard exercise of an extended interval nature does not yield the best training response.

Implication. Ultra-short training produces aerobic and alactacid energy training effects, as well as competition-specific neuromuscular training effects. It is possibly, the best form of training for individuals who have to compete at heavy workloads for extended periods.

The physiological responses of two males to running at 20 km/h on a horizontal treadmill were investigated. Work and rest periods from 5 to 15 seconds in various combinations for a total period of 30 minutes were preformed. A continuous run at the selected pace was also investigated.

Both Ss responded differently to the conditions. One S had less work capacity than the other requiring "lighter" workloads to avoid detrimental fatigue. This observation confirmed the need to individualize training programs if all participants are to receive the best effects from training experiences.

Both Ss reached oxygen uptakes during intermittent running close to or equal to their maximum. For one S the work to rest ratio of 15 seconds to 15 seconds, and for the other 10 seconds to 5 seconds, produced the maximal response.

Several relationships were found among the iterations of duration, distance, and work:rest ratios.

For both Ss at this running velocity, work periods of 15 seconds were excessive, while 5 and 10 seconds were not.

Under continuous running at 20 km/h, one S could only continue for 3 minutes while the other performed for 4 minutes. The amount of work performed, and therefore the potential to gain benefits from training, became less as the duration of work and accumulation of anaerobic metabolites increased.

With short work and rest intervals, it is possible to perform a substantial volume of high-intensity work supported by primarily aerobic metabolism.

"Two physically trained subjects can run continuously for 3 or 4 minutes respectively on a treadmill at a speed of 20 km/h, reaching maximal values for oxygen uptake and for blood lactic acid. At the end of this time when they have run a total distance 1 and 1.3 km respectively, they will be totally exhausted and will need a comparatively long time for recovery. Running at the same speed, but intermittent with short spells of activity and rest, the character of work will change entirely; despite a marked decrease in oxygen uptake during the actual work periods, the work can be performed without or with only a comparatively slight increase in blood lactic acid concentration, indicating aerobic or practically aerobic work conditions. The trained subjects can stand an effective work time of 15 or 20 minutes respectively, within the experimental time of 30 minutes, and run a total distance of 5 or 6.67 km respectively, without being totally exhausted." (p. 286)

Implications. Several guidelines for planning effective training programs are inherent in this study.

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. These oxygen sources are repeatedly 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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