Complete Reversion of Cardiac Functional Adaptation Induced by Exercise Training
Long-term exercise training is associated with characteristic cardiac adaptation, termed athlete's heart. Our research group previously characterized in vivo left ventricular (LV) function of exercise-induced cardiac hypertrophy in detail in a rat model; however, the effect of detraining on LV function is still unclear. We aimed at evaluating the reversibility of functional alterations of athlete's heart after detraining.Methods
Rats (n = 16) were divided into detrained exercised (DEx) and detrained control (DCo) groups. Trained rats swam 200 min·d−1 for 12 wk, and control rats were taken into water for 5 min·d−1. After the training period, both groups remained sedentary for 8 wk. We performed echocardiography at weeks 12 and 20 to investigate the development and regression of exercise-induced structural changes. LV pressure–volume analysis was performed to calculate cardiac functional parameters. LV samples were harvested for histological examination.Results
Echocardiography showed robust LV hypertrophy after completing the training protocol (LV mass index = 2.61 ± 0.08 DEx vs 2.04 ± 0.04 g·kg−1 DCo, P < 0.05). This adaptation regressed after detraining (LV mass index = 2.01 ± 0.03 vs 1.97 ± 0.05 g·kg−1, n.s.), which was confirmed by postmortem measured heart weight and histological morphometry. After the 8-wk-long detraining period, a regression of the previously described exercise-induced cardiac functional alterations was observed (DEx vs DCo): stroke volume (SV; 144.8 ± 9.0 vs 143.9 ± 9.6 μL, P = 0.949), active relaxation (τ = 11.5 ± 0.3 vs 11.3 ± 0.4 ms, P = 0.760), contractility (preload recruitable stroke work = 69.5 ± 2.7 vs 70.9 ± 2.4 mm Hg, P = 0.709), and mechanoenergetic (mechanical efficiency = 68.7 ± 1.2 vs 69.4 ± 1.8, P = 0.742) enhancement reverted completely to control values. Myocardial stiffness remained unchanged; moreover, no fibrosis was observed after the detraining period.Conclusion
Functional consequences of exercise-induced physiological LV hypertrophy completely regressed after 8 wk of deconditioning.