Objectives
This study examined the influences of the volume of all-out sprint-interval exercise (SIE) on acute post-exercise heart rate variability (HRV) recovery.
Methods
HRV recovery following a session of (i) 2 × 30-s SIE (SIE
2
), (ii) 4 × 30-s SIE (SIE
4
), and (iii) non-exercising control (CON) were compared in 15 untrained young males. Time domain [standard deviation of normal-to-normal intervals, root mean square of successive R-R differences] and frequency domain [low frequency (0.04–0.14 Hz), high frequency (0.15–0.40 Hz)] measures of HRV were assessed every 20 min for 140 min after the exercise, and every hour during the first 4 h of actual sleep time at immediate night. All trials were scheduled at 19:00.
Results
In comparison to CON, both SIE
2
and SIE
4
attenuated the HRV markedly (
p
< 0.05), while the declined HRV restored progressively during recovery. Although the sprint repetitions of SIE
4
was twice as that of SIE
2
, the declined HRV indices at corresponding time points during recovery were not different between the two trials (
p
> 0.05). Nevertheless, the post-exercise HRV restoration in SIE
2
appeared to be faster than that in SIE
4
. Regardless, nocturnal HRV measured within 10 h following the exercise was not different among the SIE and CON trials (
p
> 0.05).
Conclusion
Such findings suggest that the exercise volume of the SIE protocol may be a factor affecting the rate of removal of the cardiac autonomic disturbance following the exercise. In addition, rest for ∼10 h following either session of the SIE protocol appears to be appropriate for the cardiovascular system to recover.