RESUMEN
It is hypothesized that estradiol levels, as well as aging, influence cardiac autonomic function in women. The main aim of this study was to test the correlations between heart rate recovery (HRR) dynamics, as a proxy of cardiac autonomic function, with estradiol levels and age in women. This cross-sectional study involved 44 healthy women. Heart rate (HR) data were obtained beat-by-beat during the entire experiment. Maximal incremental exercise testing (IET) on a cycle ergometer was performed followed by 6 min of recovery. During the IET recovery period, the overall HRR dynamics were evaluated by exponential data modeling (time constant "τ") where shorter τ indicates faster HRR adjustment. Considering the cardiac autonomic complexity, HRR dynamics were also evaluated by delta (Δ) analysis considering different HR data intervals. The relationship between HRR dynamics, estradiol levels and age was tested by Pearson product-moment correlation. The overall HRR dynamics (i.e., τ) were statistically correlated with age (r = 0.58, p < 0.001) and estradiol levels (r = -0.37, p = 0.01). The Δ analysis showed that the slower overall HRR associated with aging was a consequence of slower dynamics occurring within the 45-210 s interval, indicating slower sympathetic withdrawal. In conclusion, aging effects on HRR in women seems to be correlated with a slower sympathetic withdrawal. In addition, the cardioprotective effect previously associated with estradiol seems not to influence the autonomic modulation during exercise recovery periods in women.
RESUMEN
Os objetivos deste estudo foram determinar o limiar de anaerobiose (LA), utilizando um teste de esforço físico dinâmico em degraus descontínuos (TEFDD) em esteira rolante, por meio da resposta da freqüência cardíaca (FC), analisar sua variabilidade (VFC), bem como verificar a adequação do protocolo de treinamento, baseado no LA. Dois homens, de 56 e 61 anos, portadores de fatores de risco e/ou doença cardiovascular instalada, foram submetidos ao TEFDD, que consistiu na realização de 4 velocidades distintas com duração de 6 minutos cada, a partir da qual foi determinado o LA por meio da aplicação de um modelo semiparamétrico aos dados de FC. Foram analisadas FC média e sua variabilidade, pelo índice temporal RMSSD dos intervalos R-R em milissegundos em cada velocidade avaliada. A partir dos resultados verificamos que a metodologia utilizada foi adequada para identificação do LA e que o protocolo de treinamento de ambos voluntários estava sendo realizado na faixa do LA. Também foi possível observar que em intensidades mais elevadas de exercício ocorreu um predomínio da atividade simpática sobre o coração, a qual é evidenciada pelo aumento da FC juntamente com a redução da VFC.
The purposes of present study were determine the anaerobic threshold (AT) by heart rate (HR) response and analyze the heart rate variability (VFC) during a discontinuous dynamic physical exercise protocol (DDPEP) at treadmill and, additionally, verify if the training performed by the subjects is adequate when the LA is considered. Two 56 and 61 years-old men, with risk factor and/or cardiovascular disease, performed a DDPEP at a treadmill. This protocol was constituted by 4 different velocities with 6 minutes duration in which a semi parametric model was applied to determine the AT. In each velocity, the average of HR and HRV, which was analyzed by the RMSSD index of R-R intervals in milliseconds, were calculated. The results suggest that the method utilized was adequate to AT determination, confirming that the training performed by the subjects was realized at intensities close to the AT. In addition, a predominance of sympathetic activity on the heart was observed at the higher efforts intensities which was confirmed by increased HR and decreased HRV.