[Genders characteristics of aerobic endurance exercise performance and autonomic regulation in cold environments]

This study examined the regulatory effects of autonomic nervous system on aerobic endurance exercise performance in cold exposure, focusing on heart rate recovery (HRR) and heart rate variability (HRV) across genders. Thirty participants (17 males and 13 females) from a university track endurance program, classified as exercise grade II or above, underwent monitoring of HRV in time domain, frequency domain, nonlinear correlation indices and 1 min HRR. Measurements were taken before, during, and after aerobic endurance exercise in cold and normal environments, respectively. The results were as follows. (1) The duration of aerobic endurance exercise completed by all the subjects in cold environment was significantly increased compared with that in normal environment. The 1 min HRR after aerobic endurance exercise in cold environment was significantly lower than that in normal environment, and the decrease in the males was significantly higher than that in the females. (2) The time domain analysis results showed that, prior to the aerobic endurance exercise, there were no significant difference of standard deviation from the mean value of normal to normal intervals (SDNN), root mean square of successive differences (RMSSD), and percentage of adjacent normal-to-normal intervals differing by more than 50 ms (pNN50) between cold and normal environments. During aerobic endurance exercise in cold environment, SDNN, RMSSD and pNN50 were significantly higher than those in normal environment, with the females showing significantly greater increases compared with those of the males. The levels of SDNN, RMSSD and pNN50 in the males at different time points under different environments were significantly lower than those in the quiet state; The levels of SDNN and RMSSD of the females at different time points under different environments were significantly lower than those in the quiet state, while the pNN50 at different time points under cold environments was significantly lower than that in the quiet state. (3) Frequency domain analysis results showed that, prior to the aerobic endurance exercise, there was no significant difference of high frequency normalized units [HF (n.u.)], low frequency normalized units [LF (n.u.)] and LF/HF ratio between cold and normal environments. During aerobic endurance exercise in cold environment, the levels of HF (n.u.) significantly increased compared to normal environment in the females, while LF (n.u.) and LF/HF ratio levels significantly decreased compared to normal environments. The levels of HF (n.u.), LF (n.u.) and LF/HF ratio of different genders at different time points in the different environments showed no significant changes, compared to those in the quiet state. (4) Non-linear analysis results showed a significant increase in SD1 (standard deviation perpendicular to the line-of-identity)/SD2 (standard deviation along the line-of-identity) ratio during aerobic endurance exercise in cold environment in the females, while no significant changes were observed in the males. SD1/SD2 ratios in the males at different time points and in the females at 1 min under cold environments were significantly higher than those in the quiet state. These findings suggest that aerobic endurance performance increases during cold exposure, accompanied by gender-specific differences in the regulation of autonomic nervous system. Females exhibit higher vagal activity and faster autonomic nervous system recovery compared to males.