ABSTRACT
Objective To explore the effectiveness of 12-week exercises with different intensities on cardiorespiratory fitness(CRF)of rats,so as to provide theoretical evidences for evaluating effective exercise loads.Methods Forty male Wistar rats were randomly divided into a low intensity group(50％ VO2max),a moderate intensity group(65％VO2max),a high intensity group(80％VO2max)and a sedentary group,each of 10.All rats were measured the VO2max after three-day adaptive training,then they were repeated the VO2max test every two weeks on the non-training days and the load of the next two weeks was adjusted according to the test result.The treadmill speed was controlled to maintain the specific exercise intensity of each group in the training period.The rats in the exercise groups were trained 5 days per week and 60 minutes per day.After 12 weeks of exercise intervention,the ultrasonic cardiogram tests were conducted.Results After 12 weeks of exercise,compared with the sedentary group,the average weight of the low and high intensity groups decreased significantly(P＜0.05,P＜0.01).After the 12-week exercise intervention,the average VO2max of the three exercise groups were significantly higher than the sedentary group (P＜0.01).The average CRF of the moderate and high intensity group improved faster,with their peak value at the 6th and 8th week respectively.However,in the low intensity group significant improvement in the average CRF was observed from the 10th week,with the peak value appearing at the 12th week.The average left ventricular internal dimension systole of the high intensity group was lower than the low intensity group(P＜0.05),while the ejection fraction and left ventricular shortening fraction increased significantly (P＜0.05).Conclusions Exercises with different intensity can improve the CRF.However,compared with moderate and high intensity exercise,it requires longer time to improve CRF with low intensity exercise.Only exercise with 80％VO2max can significantly improve the cardiac pumping function.