Pilot Study on Exercise Performance Level and Physiological Response According to Rest Intervals between Sets during 65% 1RM Bench Press Exercise

The purpose of this study was a pilot study to determine the performance level and physiologic responses (heart rate and heart rate recovery (%)) of six different rest interval conditions during the performance of seven sets of a 65% 1RM bench press exercise. Eight healthy male university students who were 20 years of age and enrolled at University C were tested. The subjects’ bench press 1RM was measured before the experiment, and they performed bench press exercises with six different rest intervals (30 s, 1 min, 2 min, 3 min, 4 min, and 5 min), which were randomized and crossed over. The experimental measurements were performed once a week and repeated six times per rest interval condition (six intervals) to minimize the learning effect for the subjects. A two-way repeated measures ANOVA was used to verify the data, post-comparison (contrast: repeat) was used to establish statistical significance, and the following results were obtained. First, the level of exercise performance (reps) between sets across the six rest interval conditions showed significant differences (p < 0.000) and high effect sizes (ES ≥ 0.70) across the rest interval conditions. In addition, more reps (in terms of volume) were performed in the relatively longer rest interval conditions. The number of reps over the progression of the sets also showed a significant difference (p < 0.000) for the shorter rest interval condition, with a high effect size (ES ≥ 0.64). There was also an interaction effect (p < 0.000) between the rest interval condition and the set, with the number of repetitions at the beginning of the set decreasing significantly as the set progressed for the relatively short rest interval condition, with a high effect size (ES ≥ 0.60). Second, there was no statistically significant difference in after-exercise heart rate among the rest interval conditions between sets, but the longer rest interval conditions of 4 and 5 min showed a significant difference (p < 0.005) as the set progressed, with a high effect size (ES ≥ 0.41). In each of the six rest interval conditions, heart rate levels were similar in sets 1 and 2 but increased from set 3 to set 7. Immediately after each bout of exercise, the resting heart rate according to rest interval condition was statistically highest in the shorter rest intervals (30 s, 1 min), with a high effect size (p < 0.020) and a high ES ≥ 0.39. Heart rate was also higher in the 2, 3, 4, and 5-min rest intervals, and increased significantly (p < 0.000) as the sets progressed, with a high effect size. Third, heart rate recovery (%) according to the rest interval condition between sets was significantly higher in the longer rest interval conditions (1, 2, 3, 4, and 5 min) than in the 30 s rest interval condition (p < 0.039), with a high effect size (ES ≥ 0.37). In addition, heart rate recovery in all rest interval conditions significantly decreased as the sets progressed (p < 0.05), with a high effect size (ES ≥ 0.37). Taken together, there were significant differences in performance levels (reps), physiological responses, and recovery between rest interval conditions during the equal-intensity resistance exercises in this study. Furthermore, the performance levels between rest interval conditions during the 65% 1RM bench press exercise in this study suggest that rest intervals of 2–3 min may be effective for improving muscular endurance, while rest intervals of 4–5 min may be effective for improving muscle hypertrophy. This suggests that manipulating the rest intervals between sets during resistance training at the same intensity may lead to better training outcomes.