Background Athletes are generally considered a healthy population, but due to intensive training they can often experience health problems. Regular endurance exercise training induces structural and electrical cardiac remodelling, which enable optimal oxygen delivery for increased metabolic requirements. Electrical adaptations seen as heart rate and heart rate variability (HRV) changes depend mostly on autonomic nervous system activity adaptations to endurance training. HRV analysis has been proved as useful non-invasive method for evaluating the overall state of cardiovascular system, as well as the state of autonomic nervous system that regulates cardiac activity. In comparison with sedentary people, parasympathetic nervous system of well-trained athletes often has higher tone, which is reflected in increased high-frequency (HF) component of HRV.
Aim The aim of this study was to evaluate the correlation of cardiac electrical remodelling (as reflected in HRV) with athlete’s training status, their maximal oxygen consumption (VO2max), and structural cardiac remodelling (reflected in cardiac output).
Methods Cross-sectional study was conducted on a group of 33 Slovenian male and female rowers (age 18.9 ± 3.5 years), as rowing is one of the sport disciplines associated with the highest oxygen consumption, therefore a substantial cardiac remodelling effect of endurance exercise training was assumed for our subjects. Five minute resting enhanced ECG was recorded in order to examine HRV parameters. VO2max was determined by the ergometer testing and ultrasound measurements were used to estimate cardiac output.
Results No statistically significant differences (p > 0.05) were observed in HRV parameters between athletes with short-term training status ( < 4067 hours of training) and long-term training status ( ≥ 4067 hours of training). However, significant correlations were observed between training status and low frequency (LF) component (r = 0.657, p = 0.006), high frequency (HF) component (r = 0.629, p = 0.009), and LF/HF ratio (r = 0.675, p = 0.004) within the long-term training status group. There were no statistically significant differences (p > 0.05) in HRV parameters between athletes with lower VO2max ( < 62 ml/kg min) and higher VO2max ( ≥ 62 ml/kg min): LF (p = 0.65), HF (p = 0.52), LF/HF ratio (p = 0.60). Nevertheless, a curvilinear, weak, but significant relation was observed. Additionally, cardiac structural remodelling induced by endurance training might also affect HRV parameters, but this factor was excluded in the present study, because no significant differences (p > 0.05) was observed between HRV parameters and cardiac output.
Conclusions There is substantial variability in the studied parameters among athletes. However, changes in cardiac electrical remodelling as reflected in HRV among athletes with long-term training status and among athletes with maximal oxygen consumption (VO2max) were observed.
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