Effects of resistance exercise involving different intra-set rest distributions on muscular performance, metabolic, hormonal and cardiovascular responses in resistance-trained men: a randomized crossover study

Abstract

This study compared the acute effects of traditional (TRD) and two intra-set rest resistance exercise (RE) structures—cluster sets (CLS) and inter-repetition rest sets (IRS)—on muscular performance, cardiovascular responses, metabolic and perceptual fatigue, and endocrine markers in resistance-trained men. Ten participants (age: 31±7.3 years; training experience: 5.1±2.3 years) completed six RE sessions involving three bilateral knee extension sets of 10 repetitions at 70% 1RM. Sessions were randomized and separated by ≥5 days. Each protocol (CLS, IRS, TRD) was performed twice—once for performance outcomes (maximum number of repetitions [MNR], total load lifted [TLL]) and once for physiological measures (blood lactate, rating of fatigue [ROF], growth hormone [GH], insulin-like growth factor 1 [IGF-1], heart rate [HR], blood pressure [BP], and rate-pressure product [RPP]). No significant condition × time interactions were observed for cardiovascular measures (BP, HR, RPP, all p>0.05), and area under the curve analysis showed no significant differences between protocols. Both CLS and IRS yielded significantly higher MNR and TLL versus TRD (p<0.05). Post-exercise lactate and ROF were highest in TRD and lowest in IRS (p<0.05). GH increased significantly immediately post-exercise in all protocols (p<0.001), with no between-group differences. IGF-1 increased non-significantly post-exercise and declined toward baseline after 30 minutes. Intra-set rest strategies (i.e., CLS and IRS) seems to improve acute performance and reduce fatigue without elevating cardiovascular stress beyond traditional configurations. These strategies are effective for maximizing training output while managing GH secretion, blood lactate changes, and perceptual fatigue in resistance-trained men.