Effect of repeated sprint exercises on cardiac autonomic recovery in adolescent and adult males: an experimental trial

Purpose Repeated sprint exercises (RSEs) are widely used to improve physical fitness; however, their specific effects on cardiac autonomic recovery (CAR) in individuals of different ages and biological maturation (BM) stages still lack investigation. Our objective was to analyse the effect of RSE on CAR, assessed by the heart rate (HR) recovery index and the time and frequency domains of heart rate variability (HRV) in male adolescents and adults. Methods Non-randomised experimental study. Thirty-eight individuals classified as having a high level of physical activity (males, 22 adolescents/16 adults) underwent a single session of RSE consisting of 3 rounds with 6 supra-maximal sprints interspersed with 5 minutes of passive rest. The recovery HR (between rounds) and the HRV from pre-, 20 minutes, 2 hours, and 24 hours post-RSE were assessed using short-range radio telemetry and used to calculate the CAR. In adolescents, BM was analysed using peak-height-velocity (PHV). Results Adolescents demonstrated more efficient parasympathetic reactivation than adults after RSE (η²p = 0.574, p < 0.05), especially those in the pre-PHV stage of BM ( η²p = 0.659, p < 0.05). For HRV, we identified an effect of time for both RSE groups on the mean square root of successive differences in intervals between heartbeats (RMSSD) (η²p = 0.280, p < 0.05) and the low frequency/high frequency ratio (LF/HF) ( η²p = 0.129, p < 0.05). Adolescents indicated higher values than adults for RMSSD and LF. Conclusions Parasympathetic activity is less affected in adolescents, especially pre-PHV, after RSE. In both groups, at least two hours after RSE, parasympathetic activity tended to return to baseline values, stabilising again 24 hours after RSE.