Short-term physical training alters cardiovascular autonomic response amplitude and latencies

This study reports the results of 15 days of exercise training in 25 adult males on cardiovascular autonomic response amplitude and latencies. A standard battery of autonomic function tests including both activity (tone) and reactivity was used. Parasympathetic activity as evaluated from Heart rate variability (HRV) showed no statistically significant change in both time and frequency domain measures, similarly Sympathetic activity as measured by QT/QS2 ratio showed no statistically significant change, but there was a trend of a decrease in sympathetic activity and an increase in parasympathetic activity. There were no changes in the parameters measuring parasympathetic reactivity. Sympathetic reactivity as evaluated by diastolic blood pressure responses to hand grip test (HGT) and cold pressor test (CPT) showed significant decreases. Time domain assessment of autonomic responses was done by measuring tachycardia and bradycardia latencies during Valsalva maneuver (VM) and lying to standing test (LST). Physical training resulted in a decrease in tachycardia latency during LST and a decrease in bradycardia latency during VM. We conclude from the present study that 15 days of physical training is not enough to alter autonomic activity and PNS reactivity but can result in changes in SNS reactivity and latency parameters. We hypothesize that a decrease in bradycardia latency during VM signifies a faster recovery of heart rate during VM and a decrease in tachycardia latency during LST denotes a delayed activation of the system both of which are favorable cardiovascular responses.