High Strength Training Reduces The Heart Rate Variability In Older Healthy Men

Abstract

Evaluate non-pharmacological therapies that improve the autonomic control of heart rate of older subjects has a clinical significance, since reduced heart rate variability (HRV) can be associated with higher cardiovascular morbidity and mortality rates. PURPOSE: To investigate if the strength training improves the cardiac autonomic control in healthy older men. METHODS: 9 older healthy men (62 ±2.0 years) took part of the present study. Electrocardiogram was continuously recorded for 15 min at rest, in the supine and seated position, before and after the strength training (ST) period. The effect of ST on arterial blood pressure was also assessed. To estimate the strength gains, isokinetic eccentric (ECC) knee extension and flexion peak torque (PT) of the dominant leg were measured at 60°/sec through a range from 90° to 30° knee flexion, by an isokinetic dynamometer. The ST program consisted in 2–4 sets of 8–12 repetitions of the bilateral knee eccentric flexion and extension, which was performed on the same dynamometer. Subjects trained 2d.wk-1 for 12 wk with resistance equaling approximately 70–80% of PT. Resting HR and RR intervals were analyzed by time (RMSSD index) and frequency domain methods. The power spectral components are reported in normalized units (nu) at low (LF) and high (HF) frequency, and as the LF/HF ratio. The effect of strength training was assessed by two-way ANOVA for repeated measures followed, when appropriate, by post hoc analysis. The level of significance was set at α=5%. RESULTS: Systolic blood pressure decreased (123.8 ± 8.3 to 117.7 ± 10.2 mmHg, P<0.05) and PT increased (extension: 210.0 ± 38.5 to 252.7 ± 60.9 N.m; flexion 117.6 ± 25.1 to 132.9 ± 27.3 N.m, P<0.05) after the ST. The frequency domain indices showed a significant training effect (P<0.05), since LF and LF/HF increased (supine= 57 ±14 to 68 ±14, 1.56 ±.85 to 2.35 ±1.48; seated= 65 ±15 to 74 ±8.0, 2.48 ±1.09 to 3.19 ±1.31, respectively), and HF decreased (supine= 43 ±14 to 32 ±14; seated= 35 ±15 to 26 ±8). CONCLUSION: The results of the present investigation suggest that high strength eccentric training, performed by older healthy men, increase the peak torque and reduce the blood systolic pressure. However, it causes an autonomic imbalance into sympathetic predominance, which mechanism is not clear.