INTRODUCTION: Prior investigations in post-myocardial infarction and healthy elderly subjects have established that heart rate variability (HRV) predicts mortality. Predominantly cross-sectional studies have shown an association between endurance training and measures of HRV. In a randomized trial, this study sought to prospectively compare the effects of endurance and strength training on HRV in 45 healthy elderly females (average age 69.9 +/- 0.9 years). METHODS: All subjects were rigorously screened to be normal by history, physical, blood tests, ECG, ETT and echocardiogram. All subjects were monitored for 24 hours by a 2-channel Holter before and after training. Artifacts and arrhythmias were manually removed. Tapes were examined for standard measures of HRV. INTERVENTION: 15 subjects were randomized to endurance trained (ET), 15 subjects to strength training (ST), and 15 subjects to no training (NT) for six months. RESULTS: Training resulted in a significant increase in VO2max in the ET (+7.4%, p = 0.005) group only. There was a small but not significant decrease in HR with both the ET and ST groups. ET resulted in a significant increase in most time domain and all frequency domain measures of HRV. ST resulted in no significant change in HRV measures. CONCLUSION: Strength training, as opposed to endurance training has no significant impact on HRV. This suggests that exercise interventions designed to improve strength (such as weight-lifting) will have little to no impact on HRV, suggesting that aerobic and strength training operate through different mechanisms to reduce cardiac risk.

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