Influence of rest interval length in between sets on hormonal responses and changes in body composition, muscular strength, and functional performance during twelve weeks of periodized resistance training in older men

Purpose: To determine: i) if strength resistance exercise protocols (SRE) with 60-second rest interval lengths (RI) between sets (SS) will elicit significantly greater acute increases in total testosterone (TT) and growth hormone (GH), compared to SRE prescribed with 4-minute RI between sets (SL); and ii) if 8 weeks of periodized strength resistance training (RT) incorporating 60-second RI in between sets (SSRT) will induce greater improvements in body composition and muscular performance, compared to the same RT program incorporating 4-minute RI (SLRT).;Methods: 22 men (SSRT: n=11, 65.6±3.4 years; SLRT: n=11, 70.3±4.9 years) were assigned to one of two groups, following 4 weeks of periodized hypertrophic RT (PHRT). From Week 4 to Week 12, SSRT and SLRT followed the same periodized strength RT program, with RI the only difference in RT prescription. 18 of the 22 participants completed 1 acute hypertrophic RE protocol (HRE), prior to the 12-week periodized RT program, and 2 SRE; SRE 1 was completed at Week 4 and SRE 2 upon completion of the RT program (Week 12). Blood was drawn pre- (PRE), immediately post- (POST), 15 minutes post- (15 MIN), and 30 minutes post-exercise (30 MIN), to determine blood concentrations of TT and GH.;Results: Following PHRT, all study participants experienced increases in lean body mass (LBM) (p<0.01), maximal upper and lower body strength (p<0.001), stairclimbing power (p<0.001), and dynamic balance (p<0.05). All study subjects experienced significant decreases in percentage body fat (p<0.05), stairclimbing time (p<0.001), and 400-meter walking time (p<0.001). Across the 8-week strength RT phase, compared to SLRT, SSRT experienced significantly greater increases in LBM (p=0.001), upper and lower body maximal strength (p<0.01), and stairclimbing power (p<0.001). HRE (n=18) increased TT, from PRE to POST, 15 MIN, and 30 MIN (p±.05); for GH, elevations above PRE were also significant at POST, 15 MIN, and 30 MIN (p<0.01). In response to SRE 1 and SRE 2, there was a significant effect for protocol on TT acute change ([POST] – [PRE]) (p<0.001) and percent change ([POST – PRE]/[PRE]) (p=0.001); the acute elevations in TT in response to SS were significantly greater, compared to SL. There was also a significant effect for protocol on GH percent change (p=0.003); the acute elevations in GH in response to SS were significantly greater, compared to SL.;Conclusions: Strength resistance exercise with short rest interval lengths in between sets increases acute TT and GH responses in older men, while long rest interval lengths in between sets blunt the acute TT and GH response to strength resistance exercise. Further, 8 weeks of periodized high-intensity strength RT with short rest interval lengths in between sets induces significantly greater enhancements in body composition, muscular performance, and functional performance, compared to the same RT prescription with long rest interval lengths in between sets.;Practical Applications: This study gives insight into a new approach to prescribing strength resistance exercise and periodzed strength resistance training for older men, in order to optimize hypertrophic and performance adaptations to short-term strength resistance training and maximally offset the age-related declines in lean body mass, strength, and power.;Acknowledgements: This study received funding through the National Strength and Conditioning Association Foundation (NSCAF).