Rundell, K. W. (1994). Strength and endurance: Use it or lose it. Olympic Coach, 4(1), 7-9.

An injury or illness which keeps an athlete from training for as brief a period as 10 days can have a serious effect on performance. This is referred to as the "reversibility concept" (of detraining), which means that the positive changes from training (adaptations) are lost as a result of the body adjusting to a lesser physical demand and peak condition deteriorates rapidly. (p. 7)

The amount of blood that the heart can pump to working muscles is the cardiac output. This is assisted by the following exercise induced changes:

(a) increased capillaries in the exercised muscles; and
(b) increased mitochondria and mitochondrial enzymes which aid in the use of fuel sources.

These two effects allow muscles to decrease the amount of lactate produced for a given workload, that is, the anaerobic threshold is improved. These circulatory and muscle adaptations result in increased aerobic capacity and increased endurance.

Coyle, Martin, and Holloszy (1984) studied endurance athletes who had been training for 10 years. VO2max decreased by 7, 13, and 15 percent after 12, 56, and 84 days. Stroke volume decreased by 11% after 12 days. Exercise stroke volume and HRmax did not change any further after 12 days, with maximum cardiac output remaining 7-9% below that of the trained state. Thus, maximum cardiac output reduction occurs mostly in the first 12 days, while VO2max and mitochondrial activity continue to decline for some time after that before stabilizing.

Thus, features of circulation used to indicate a trained state may be misleading because of their differential response to exercise and exercise cessation when compared to other facets of aerobic adaptation (particularly peripheral adaptations).

[Coyle, E. F., Martin W. H., & Holloszy, J. O. (1984). Cardiovascular and metabolic rates of detraining. Medicine and Science in Sports and Exercise, 15, 158. (abstract)]

Ready and Quinney (1982) showed that AnT drops as fast as VO2max in detraining almost in concert with mitochondrial enzyme decrease. However, after 9 weeks the detrained level was still well above the pre-trained level which indicates that not all gains are lost through detraining.

[Ready, A. E., & Quinney, H. A. (1982). Alterations in anaerobic threshold as the result of endurance training and detraining. Medicine and Science in Sports and Exercise, 14, 292-296.]

It is often proposed that previously endurance-trained athletes rebound faster than non-athletes after detraining. That is not the case. Even though the heart's ability to pump additional blood is restored within days after resuming training, enhanced enzyme production in the cells takes longer. Regain rates are much slower than loss rates. If an athlete stops training for 12 days only 75 percent of enzymes lost will be regained after 24 days of retraining.

Once again, circulatory indices could mislead inferences about a trained state because of their different reaction to exercise stress when compared with peripheral reactions.

Since a complete stop to training has a much more negative effect than merely reducing training volume capacity, it is important for athletes to have as little down time as possible.

Maintenance Training

Training for as little as two days per week is enough to maintain endurance performance, provided that the exercise intensity is high (85-100% VO2max). Anaerobic threshold can be maintained during periods of reduced training by as few as one high intensity training session per week.

As with endurance training, the maintenance of resistance training adaptations appear to be related to exercise intensity rather than exercise frequency or duration. During the competitive season, strength can be maintained by one heavy session per week.

Maintenance programs are useful for periods of travel adaptation, high stress levels from other sources, and when localized injury prevents total body use. It is sufficient to perform fewer high intensity programs to prevent training adaptation loss (one to three per sessions per week). However, such a reduced training program cannot be sustained indefinitely without some eventual detrimental loss.

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