Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices.

Abstract

This study investigated non-invasive indices of post-exercise parasympathetic reactivation (using heart rate variability, HRV) and sympathetic withdrawal (using systolic time intervals, STI) following different exercise durations. 13 healthy males (age 26.4±4.7years) cycled at 70% heart rate (HR) reserve for two durations-8 min (SHORT) and 32 min (LONG)-on separate occasions: HRV (including natural logarithm of root mean square of successive differences, Ln-RMSSD) and STI (including pre-ejection period, PEP) were assessed throughout 10 min seated recovery. Exercise HR was similar between SHORT and LONG (146±7 and 147±6 bmin-1, respectively; p=0.173), as was HR deceleration during 10 min recovery (p=0.199). HR remained elevated above baseline (p<0.001) throughout recovery for both trials (SHORT 82±13 bmin-1; LONG 86±10 bmin-1, at 10 min post-exercise). Ln-RMSSD was similar at end-exercise between trials (SHORT 1.10±0.30ms; LONG 1.05±0.73ms; p=0.656), though it recovered more rapidly following SHORT (p=0.010), with differences apparent from 1 min (SHORT 2.29±1.08ms; LONG 1.85±0.82ms; p=0.005) to 10 min post-exercise (SHORT 2.89±0.80ms; LONG 2.46±0.70ms; p=0.007). Ln-RMSSD remained suppressed below baseline throughout recovery following both trials (p<0.001). PEP was the same at end exercise for both trials (70±6ms), with exercise duration having no effect on recovery (p=0.659). By 10 min post-exercise, PEP increased to 130±21ms (SHORT) and 131±20ms (LONG), which was similar to baseline (p≥0.143). Prolonged exercise duration attenuated the recovery of HRV indices of parasympathetic reactivation, but did not influence STI indices of sympathetic withdrawal. Therefore, duration must be considered when investigating post-exercise HRV. Monitoring these measures simultaneously can provide insights not revealed by underlying HR or either measure alone.