Autonomic Modulation After Acute Resistance Exercise in Resistance-Trained Individuals

Abstract

Differences in autonomic modulation between free-weight and weight machines resistance exercise is unknown. PURPOSE: To investigate the effects of acute free-weight (FW) and weight machines (WM) resistance exercise on heart rate complexity (HRC) and variability (HRV) in resistance-trained individuals. METHODS: Resistance- trained individuals were assigned to either a FW (n = 25) or a WM (n = 16) group. Autonomic modulation was collected at rest, and 15 (Rec1) and 25 (Rec2) min following acute resistance exercise (ARE) or a control. Sample Entropy (SampEn), indicative of vagal modulation, was used as a measure of HRC. HRV measurements included vagal modulation (normalized high frequency (HFnu)), and sympathovagal balance (LF/HF ratio). ARE for the FW group consisted of 3 sets of 10 repetitions at 75% 1-repetition maximum (1RM) on the squat, bench press, and deadlift, while the WM group utilized of 3 sets of 10 repetitions at 75% 1RM on the leg press, lat pull down, leg extension, chest press, and leg curl. A 2x2x3 ANCOVA was used to examine groups (FW, WM) across conditions (ARE, control) and time (Rest, Rec1, Rec2), with load as a covariate. RESULTS: The groups were similar (p>0.05) for age, height, weight, BMI, and baseline autonomic modulation, but differed for years of training. There was a significant group by condition by time interaction (p=0.03) for SampEn such that in the FW group (Rest: 1.5±0.3; Rec1: 1.1±0.3; Rec2: 1.1±0.4) it was attenuated during Rec1 and Rec2 after ARE compared to rest and the control. In the MW group, while there were no significant differences from rest to Rec1 or Rec2, there was a significant difference from Rec1 to Rec2 (Rest: 1.4±0.5; Rec1: 1.0±0.3; Rec2: 1.3±0.3) such that it differed from the control. There was also a significant group by time interaction for HFnu (Rest: 62.5±15.0%; Rec1: 29.5±18.9%; Rec2: 29.2±19.9%, p=0.002) such that it was attenuated compared to rest, and the control, in both groups. The LF/HF ratio (Rest: 61.0±52.1; Rec1: 420.0 ±424.7; Rec2: 456.7±390.2, p=0.007) was augmented such that it differed from rest, and the control, in both groups. CONCLUSIONS: Based on our data the use of free- weight resistance exercises results in significant reductions in vagal modulation that are immediate, and maintained, up to 30 min, which does not appear to occur when using weight machines.