Influence of the Duration of a Treadmill Walking Bout on Heart Rate Variability at Rest in Physically Active Women

BACKGROUND: Heart rate variability (HRV) has been promoted as a noninvasive method of evaluating autonomic influence on cardiac rhythm. Although female subjects predominate in the walking studies, no study to date has examined the influence of the duration of a moderate intensity walking physical activity bout on HRV in this population. METHODS: Twelve healthy physically active middle-aged women undertook 2 conditions; 20min (W20) and 60min (W60) bouts of walking on a treadmill. Resting HRV measures were obtained before (-1 h), and 1 h and 24 h after the walking bouts. RESULTS: Mean NN interval (ie, normal-to-normal intervals between adjacent QRS complexes) was significantly lower (P = .017) at +1 h in W60 (832, 686-979ms) compared with W20 (889, 732-1046ms). A borderline main effect for time was observed for both the SDNN intervals in W60 (P = .056), and for low frequency (LF(abs)) power in W60 (P = .047), with post hoc tests revealing a significant increase between -1 h (51, 33-69 ms and 847, 461-1556 ms(2)) and +1 h (65, 34-97ms and 1316, 569-3042 ms(2)) for SDNN and LF(abs) power, respectively, but no increase at +24h compared with -1 h. CONCLUSIONS: It appears that a walking bout of 60 min duration does alter cardiac autonomic influence in healthy active women, and this alteration is not evident after 20 min of walking. Given the rather subtle effect, further studies with larger sample sizes are required to explore the nature of the changes in cardiac autonomic influence following a prolonged bout of walking.