Acute effects of different load intensities and rest intervals on muscle strength endurance in male college athletes

The purpose of this study was to compare the effects of different load intensities with rest intervals between sets on heart rate, rating of perceived exertion (RPE), power output, and blood lactate concentration during a squat strength endurance training protocol. A total of 4 sets of strength endurance tests were performed on 15 national Level 2 or above athletes with different load intensities (30% of 1 repetition maximum (1RM), 50% 1RM) and different rest intervals between sets (1 min, 2 min), 20 reps per set. Mean power (P -mean), mean heart-rate (HRmean) and RPE variations during the exercise were collected by using a linear position transducer, heart rate monitor, and Borg 6-20 scale. Besides, finger blood was collected before and after the exercise, and analyzed by using a blood lactate analyzer. HRmean, P-mean and RPE values were significantly higher at 50% 1RM load intensity than at 30% 1RM (p < 0.01), HRmean was significantly higher at 1 min rest interval than at 2 min between sets, while P-mean was significantly higher at 2 min rest interval than at 1 min between sets (p < 0.05); at 30% 1RM loading intensity, blood lactate concentrations were significantly higher at the completion of exercise for the 1 min rest interval between sets than for the 2 min (p < 0.01). However, at 50% 1RM loading intensity, blood lactate increased similarly at the completion of training in multiple sets, independent of the rest interval between sets. From a practical point of view, the results suggest that a 1 min rest interval between sets may be sufficient in a strength endurance training protocol when the load intensity is 30% 1RM. However, when the load intensity is 50% 1RM, we suggest that a 2 min rest interval between sets is required for optimal recovery and maintenance of power output.