Cardiac Parasympathetic Reactivation and Simulated Rugby Sevens

Abstract

Purpose: Cardiac parasympathetic reactivation (PR) following exercise mirrors a restoration of cardiovascular homeostasis and possibly readiness to perform. It has been postulated that a facilitated post-exercise PR may improve the peak sympathetic response during subsequent exercise. The maintenance of sympathetic drive is of importance during Rugby Sevens where athletes compete at maximal intensities repeatedly within a two-day tournament with short recovery periods between matches. This study aimed to determine whether a facilitated PR via cold water immersion (CWI) following simulated Rugby Sevens would influence markers of sympathetic drive, repeated sprint (RS) performance and subjective perceptions of recovery across six matches within a two-day tournament. Methods: Ten, male, trained, team sport athletes (24.7±2.9 yr; 180.6±3.8 cm; 88.2±9.4 kg) completed six Rugby Sevens match simulations over two days with a post-match intervention of either passive recovery (PAS; 5min, air 20°C) or CWI (5min, water 14°C) in a randomized cross-over design. Parasympathetic reactivation was inferred from heart rate variability (HRV) before and after each match. Sympathetic drive was inferred from the mean (HRmean) and peak (HRpeak) heart rate response during the RS task, first (FH) and second (SH) halves of each match and post-match blood lactate (BLApost-match). RS performance was calculated as time taken (s) to complete 6 x 30m sprints on a 20-s cycle within the first half of each match. Subjective recovery was determined via a six item 10-point questionnaire. Results: There were no significant effects of time or condition on pre-match HRV, while CWI elicited on average a 13±1.7% greater post-intervention HRV than PAS (P < .01). HRmeanRS was significantly impaired during matches four (P < .01) and six (P < .01) vs. match one, and tended towards the same during match five (P = .06). HRpeakRS was similarly impaired during match four vs. match one (P < .01) and tended towards the same during match six (P = .07). HRmeanFH was significantly impaired during matches four (P < .01) and six (P < .05) vs. match one. HRpeakFH was significantly impaired during match four vs. match one (P < .05). The average impairment in HRpeakRS was lower with CWI than PAS (-0.5±1.5% vs. -2.1±1.9%, P < .05) and tended towards the same for HRmeanRS (-1.2±1.3% vs. -2.8±2.6%, P = .09). There was no condition effect on BLApost-match but a significant decrease during match six vs. match one was observed (P < .05). There were no clear effects of time or condition on RStime (P > .05). Perceptions of physical recovery significantly decreased (P < .05), while lower body soreness and general fatigue significantly increased (P < .05) across the tournament with no clear effect of condition. Conclusion: Cold water immersion facilitated cardiac parasympathetic reactivation acutely following a simulated Rugby Sevens match. However, recovery of parasympathetic activity occurred within two hours irrespective of recovery condition. Sympathetic drive, as indicated by heart rate and blood lactate, declined across a simulated Rugby Sevens tournament, the impairment in heart rate was partially attenuated by CWI. However, there was no effect on repeated sprint performance. Subjective recovery decreased over six matches indicating an accumulation of fatigue and remained uninfluenced by CWI. Whilst acknowledging the limitations of simulated versus actual Rugby Sevens comparisons; these data indicate that CWI may be beneficial in increasing the parasympathetic recovery phase and reducing the decline in subsequent sympathetic reactivation.