PURPOSE: Aging alters cardiac autonomic function, which may contribute to a higher risk of cardiac events. Spectral measures of HR variability (HRV) and fractal-like behavior of HR are considered as markers of a healthy heart. The present study examined the effects of combining endurance and strength training compared with endurance or strength training alone on HR dynamics and physical fitness in older previously untrained men aged 40 to 67 yr. METHODS: Subjects were randomized into endurance training (E, n = 23), strength training (S, n = 25), combined endurance and strength training (ES, n = 29), or control group (C, n = 16). Short-term fractal scaling exponent (alpha1) and spectral HRV were analyzed from maximal aerobic cycling tests and during supine rest, and leg extension one repetition maximum strength was measured. RESULTS: Aerobic capacity and maximal strength increased in the training groups performing endurance and/or strength training, respectively. Only ES showed a decrease after training in fractal HR behavior during exercise, and the difference was significant between groups (p = 0.019). During supine rest, alpha1 only decreased significantly (p = 0.039) in ES from 1.18 (SD 0.20) to 1.11 (SD 0.21). The decrease in alpha1 at rest from 1.21 (SD 0.19) to 1.11 (SD 0.22) also approached significance (p = 0.061) in E. Changes in spectral measures of HRV were minor during the study period and only occurred during exercise. CONCLUSION: Fractal HR dynamics were improved more by combining strength training with endurance training in our older men compared with endurance training alone, although strength training alone produced no changes in fractal HR behavior. The synergistic effect in fractal HR behavior occurred regardless of changes in aerobic capacity.

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