Physical activity, body fat and experimental cardiac necrosis.

I. The effects of varying levels of physical activity were tested in rats, starting at ages of 21, 32 and 55 days and continuing until go, 100, 125 and 205 days. 2. Weight changes did not differ significantly between the exercise groups, except in the groups tested up to zog days, when both the exercised group and the group with limited activity were significantly lighter than the control group. 3. The weight of the soleus muscle was significantly greater in the exercised rats compared with controls and rats with limited activity, except in the oldest age-group. The weight of the tibialis anticus muscle did not differ significantly between the different exercise regimes. 4. Heart weight was not significantly affected by the exercise regime, except that in rats studied from 55 to 125 days; the group with limited activity had significantly lighter hearts than those in the control group or the exercised group. 5. The percentage body fat was lower in the exercised group compared with the limited activity group, and was less than the control group in both the rats studied up to 205 days and those studied from 21 to 90 days. 6. Isoprenaline produced less cardiac damage in the exercised rats than in controls or in rats with limited activity. Animals who died following injection of isoprenaline had a higher percentage body fat than those animals with minimal cardiac damage.