Cardiovascular responses to treadmill exercise in rats: effects of training

Abstract

Adult female rats were given a 16-wk exercise program consisting of alternate days of endurance and sprint running to study the effects of training on cardiovascular function in intact exercising animals performing treadmill exercise. Compared with an age- and body weight-matched sedentary (SED) group, in the trained group there was a 16% increase in the capacity for maximal O2 consumption (.ovrhdot.VO2 max) and a 38% increase in skeletal muscle citrate synthase activity (P < 0.05). No difference in absolute or relative heart weight was observed for the 2 groups. During submaximal exercise at the same .ovrhdot.VO2, trained rats had a 20% reduction in heart rate (P < 0.05) while O2 pulse (OP, ml O2/beat) was increased by 20% (P < 0.05) compared with the SED group. At .ovrhdot.VO2 max, trained rats had a 9% reduction in maximum heart rate (P < 0.05); slight increases (P > 0.05) in maximum stroke volume and O2 extraction combined to provide a 23% increase in OP (P < 0.05). There was no significant improvement in maximum cardiac output. These data are consistent with previous biochemical and physiological measurements on the rodent heart and suggest that no single cardiovascular variable is responsible for the increased O2 delivery seen in trained rats.