Autonomic cardiovascular modulation in masters and young cyclists following high-intensity interval training

Purpose: This study aimed at examining the autonomic cardiovascular modulation in well-trained masters and young cyclists following high-intensity interval training (HIT). Methods: Nine masters (age 55.6 ± 5.0 years) and eight young cyclists (age 25.9 ± 3.0 years) completed a HIT protocol of 6 x 30 sec at 175% of peak power output, with 4.5-min’ rest between efforts. Immediately following HIT, heart rate and R–R intervals were monitored for 30-min during passive supine recovery. Autonomic modulation was examined by i) heart rate recovery in the first 60-sec of recovery (HRR₆₀); ii) the time constant of the 30-min heart rate recovery curve (HRRτ); iii) the time course of the root mean square for successive 30-sec R–R interval (RMSSD₃₀); and iv) time and frequency domain analyses of subsequent 5-min R–R interval segments. Results: No significant between-group differences were observed for HRR₆₀ (P = 0.096) or HRRτ (P = 0.617). However, a significant interaction effect was found for RMSSD₃₀ (P = 0.021), with the master cyclists showing higher RMSSD₃₀ values following HIT. Similar results were observed in the time and frequency domain analyses with significant interaction effects found for the natural logarithm of the RMSSD (P = 0.008), normalised low-frequency power (P = 0.016) and natural logarithm of high-frequency power (P = 0.012). Conclusion: Following high-intensity interval training, master cyclists demonstrated greater post-exercise parasympathetic reactivation compared to young cyclists, indicating that physical training at older ages has significant effects on autonomic function.