Abstract
We tested the hypothesis that baseline cardiac autonomic function and its acute response
to all-out interval exercise explains individual fitness responses to high-intensity
interval training (HIT). Healthy middle-aged sedentary men performed HIT (n=12, 4–6×30 s
of all-out cycling efforts with 4-min recovery) or aerobic training (AET, n=9, 40–60 min
at 60% of peak workload in exercise test [Loadpeak]), comprising 6 sessions within 2 weeks. Low (LF) and high frequency (HF) power of
R-R interval oscillation were analyzed from data recorded at supine and standing position
(5+5 min) every morning during the intervention. A significant training effect (p< 0.001),
without a training*group interaction, was observed in Loadpeak and peak oxygen consumption (VO2peak). Pre-training supine LF/HF ratio, an estimate of sympathovagal balance, correlated
with training outcome in Loadpeak (Spearman’s rho [rs]=−0.74, p=0.006) and VO2peak (rs=− 0.59, p=0.042) in the HIT but not the AET group. Also, the mean change in the standing
LF/HF ratio in the morning after an acute HIT exercise during the 1st week of intervention correlated with training response in Loadpeak (rs=− 0.68, p=0.014) and VO2peak (rs=−0.60, p=0.039) with HIT but not with AET. In conclusion, pre-training cardiac sympathovagal
balance and its initial alterations in response to acute HIT exercise were related
to fitness responses to short-term HIT.
Key words
heart rate variability - exercise training - individual training adaptation
