Since aging decreases muscular strength particularly in the lower limb, strength training is an essential component of health promotion in older humans. However, it is unclear whether strength training is beneficial not only to muscular strength but also to the cardiovascular system. Since postexercise heart rate recovery (HRR) is an independent predictor of mortality (1), it may offer important information about this issue. Recently, we reported that HRR immediately after exercise accelerates in strength-exercise trained (ST) humans (2). Our results have been confirmed by the intervention study (3). These studies investigated postexercise HRR only in a defined time span. However, mechanisms underlying postexercise HRR are different between initial and later phases of recovery: the initial HRR is mediated via prompt parasympathetic reactivation and the later reductions are due to both continued parasympathetic reactivation and sympathetic withdrawal.
Purpose: The purpose of this study was to investigate both the initial and later HRR after exercise in ST humans.
Methods: Subjects were ST men and age-matched sedentary control (SC) men. ECG was recorded at rest (baseline), during submaximal exercise (cycling exercise, 40% maximal oxygen uptake for 8 min), and for 120 s following the exercise (the postexercise period).
Results: Both left ventricular (LV) wall thickness and LV end-diastolic dimension were greater in the ST group in comparison with the SC group. Again, LV wall thickness corrected by the end-diastolic dimension was greater in the ST humans. These results indicate that the cardiac morphology in the ST men was well adapted to strength training. Heart rate did not differ between groups at rest (ST, 58 ± 1 vs SC, 66 ± 4 bpm, p = .08), but it was lower in the ST men compared with the SC men at the end of exercise (105 ± 3 vs 113 ± 2 bpm, p = .03), and at 30 s (72 ± 3 vs 83 ± 2 bpm, p < .01), 60 s (66 ± 3 vs 77 ± 2 bpm, p = .01), 90 s (64 ± 3 vs 77 ± 2 bpm, p = .01), and 120 s (64 ± 3 vs 76 ± 2 bpm, p < .01) after the exercise. Percent HRR at 30 s (32 ± 1 vs 26 ± 2%, p = .02), 60 s (38 ± 2 vs 32 ± 2%, p = .04), 90 s (39 ± 2 vs 32 ± 2%, p = .03), and 120 s (40 ± 2 vs 32 ± 2%, p = .01) after exercise was greater in the ST group than in the SC group.
Conclusions: These results suggest that postexercise HRR in ST men is accelerated both in the initial and later phases. Strength training may improve the parasympathetic reactivation and/or the sympathetic withdrawal following exercise. The present data support emphasizing strength training as an essential component of health promotion.
(1) Cole CR, Blackstone EH, Pashkow FJ, et al. Heart-rate recovery immediately after exercise as a predictor of mortality. N Engl J Med 1999.
(2) Otsuki T, Maeda S, Iemitsu M, et al. Postexercise heart rate recovery accelerates in strength-trained athletes. Med Sci Sports Exerc 2007.
(3) Heffernan KS, Fahs CA, Shinsako KK, et al. Heart rate recovery and heart rate complexity following resistance exercise training and detraining in young men. Am J Physiol Heart Circ Physiol 2007.