Various resistance activities are used today to increase the force-generating capacity of specific skeletal muscles. Many interdependent factors influence the magnitude of improvement, but great muscular tension during training appears necessary to elicit the desired changes in muscle function. If adequate tension is to be manifested in specific muscles, they must not be excessively fatigued. Consequently, sufficient rest should be provided during and between strength-training sessions in order for recovery to occur. In addition, when other components of motor or physical fitness are concurrently being developed, precautions should be taken so that fatigue does not adversely affect strength development. In many cases, this requires the conduction of strength training and other conditioning activities during dedicated times within a session or at different times of the day.
Rest may be categorized as occurring during a training session (intratraining-session rest), between training sessions (intertraining session rest) and just before a performance or test (pre-performance rest). In order to enhance muscular tension during strength training, the phosphagen system should serve as the primary catabolic vehicle for the resynthesis of adenosine triphosphate (ATP). Five or fewer repetitions of each lift should be completed per set, and exercises involving some of the same muscle groups should be separated by about three or four minutes, depending on the trainee's recovery capacity. Specific guidelines currently are unavailable concerning intertraining-session rest due to methodological dilemmas in experiments designed to test them. The primary problems to be resolved are to identify a physiological marker indicating the point of maximal overcompensation consequent to each training session, and whether training volume should be standardized per session or per week. Evidence relating strength to pre-performance rest is meager at best. However, some preliminary work appears to indicate that 96 hours of rest may enhance strength performance as measured against a constant external load, while 48, 72 and 120 hours of rest appear to have no significant effect on moderately trained men. Although these findings are preliminary, they do seem to coincide with the effects of tapering during training for competitive swimmers.