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Male rats of 90, 150, 300, 450 or 600 days of age were placed into sedentary or physical training experimental groups. Experimental animals ran daily for 20 min at 10–20 m/min on a treadmill set at an 8-degree incline. The experimental period lasted at least 300 days. Surviving rats from each group were chosen randomly and sacrificed at 150-day intervals up to 1,050 days of age. Muscle and organ weights were analyzed by grouping animals according to their age at death and also according to their age at the initiation of the training program. Muscle and organ weight data suggest that training has a minimal affect on rats past a threshold age (approximately 450 days of age), and initiation of a training program at a late age (approximately 600 days of age) may adversely affect the rat. When the effects of age and training are combined, those attributable to age seem to be more important, supporting the view that there is a threshold age beyond which the initiation of a training program no longer affects the muscle and organ weights.

Like many other professions, coaching precipitates psychophysiological stress. Moreover, the authors found that there may be considerable stress on the coach of any sport, not just the major ones.