Comparison between continuous and intermittent physical exercise on aging rats: changes in patterns of spontaneous activity and connective tissue stability.

Life-long physical exercise increases the mean but not maximum life span of laboratory rodents. It further improves the performance in an open field setting, which suggests a delay of sensorimotor disturbances, and retards the aging increase of thermal stability of collagen. The purpose of the present study was to examine whether the amount or continuity of training is more important. We trained male Sprague-Dawley rats for 12 months from the age of 12 months in a treadmill: 1) continuously for 3 km/week (total distance covered: 144 km); 2) intermittently for 3 km/week for 8-week periods with 8-week resting periods in between (72 km), and 3) intermittently for 6 km/week for 8-week periods with 8-week resting periods in between (144 km). All training regimens prevented the increase in body weight seen in sedentary animals, although the intermittent training programs caused fluctuations with the training and resting periods. With respect to spontaneous movements in an open field setting, continuous training was most effective in counteracting age-related changes. Continuous training was also most effective for delaying age-related increase in thermal stability of collagen. We conclude that the continuity of training is more important than the amount and intensity of training.