Cardiac Autonomic Modulation and High Intensity Interval Training in Physically Inactive Men

PURPOSE: Cardiac autonomic dysfunction and physical inactivity are associated with increased risk of cardiovascular disease. Short duration high intensity interval training (HIIT) has been shown to improve aerobic capacity; however, adaptations of the cardiac autonomic nervous system are less clear. Therefore, the aim of the present study was to assess cardiac autonomic adaptations to HIIT. METHODS: In a randomised crossover controlled trial, 40 physically inactive males (21 ± 1.7 years; 179.9 ± 5.4 cm; 82.6 ± 11.5 kg; mean ±SD) completed 2-weeks of HIIT and a matched duration control period. The HIIT protocol consisted of 3 x 30-second maximal cycle ergometer sprints against a resistance of 7.5% body weight, interspersed with 1-minute of active recovery (50 rev[BULLET OPERATOR]min-1 with no resistance). In total 6-sessions were performed. Cardiac autonomic function was measured pre and post-training and control period using a plethysmographic device (Task Force® Monitor). Total power spectral density (PSD) and associated low-frequency (LF) and high-frequency (HF) power spectral components were recorded in absolute (ms2) and normalised units (nu). RESULTS: Each participant completed 18-maximal cycle ergometer sprints over a 2-week period. The HIIT intervention produced an improvement in cardiac autonomic function with significant increases in total PSD (361.8 ±200.1 vs. 19.8 ±141, p<0.001), HF (ms2) (210.6±159.3 vs.15.6±86.9, p<0.001) and HF (nu) (3.6 ±2.5 vs. 0.23 ±1.7, p<0.001), coupled with a significant decrease in LF (nu) (-3.6 ±2.5 vs. -0.23 ±1.7, p<0.001) and LF/HF ratio (-0.3 ±0.3 vs. 0.01 ±0.2, p<0.001) compared to the control period. There was no significant change in the LF (ms2) power spectral component. CONCLUSION: A short-term programme of HIIT was associated with a significant increase in cardiac autonomic modulation, demonstrated by a residual increase in cardiac vagal activity. Further research is required to establish whether these adaptations are sustained with regular HIIT training and any impact this may have on long-term cardiovascular disease risk.