High eccentric strength training reduces heart rate variability in healthy older men

BACKGROUND: Evaluation of non-pharmacological therapies that improve autonomic control of the heart rate in older subjects has a clinical significance, because reduced heart rate variability (HRV) can be associated with higher cardiovascular morbidity and mortality rates. OBJECTIVE: To investigate if strength training improves cardiac autonomic control in healthy older men. METHODS: The HRV of nine older healthy men (mean age 62 (2.0) years) was evaluated before and after 12 weeks of isokinetic eccentric strength training (2 days/week, 2-4 sets of 8-12 repetitions at 75-80% peak torque, involving knee flexion and extension. Electrocardiogram was continuously recorded for 15 min at rest, in supine and seated positions, before and after the strength training period. To estimate strength gains, the eccentric peak torque of the dominant leg was measured at 60 degrees /s by the same isokinetic dynamometer. RESULTS: Mean systolic blood pressure decreased (123.78 (8.3) to 117.67 (10.2) mmHg, p<0.05) and peak torque increased (extension 210.02 (38.5) to 252.71 (60.9) N.m; flexion: 117.56 (25.1) to 132.96 (27.3) N.m, p<0.05) after the strength training. The frequency domain indices showed a significant training effect (p<0.05), since low frequency in normalised units and low frequency/high frequency ratio increased (supine, 57 (14) to 68 (14), 1.56 (0.85) to 2.35 (1.48); seated, 65 (15) to 74 (8.0), 2.48 (1.09) to 3.19 (1.31), respectively), and high frequency in normalised units decreased (supine, 43 (14) to 32 (14); seated, 35 (15) to 26 (8)) after the training period. CONCLUSION: The results of the present investigation suggest that high eccentric strength training performed by healthy older men increases peak torque and reduces systolic blood pressure. However, an autonomic imbalance towards sympathetic modulation predominance was induced by an unknown mechanism.