PMID 32304516

Research
All papers

Heart Rate Variability After Sprint Interval Training in Cyclists and Implications for Assessing Physical Fatigue

Hebisz RG, Hebisz P, Zatoń MW

Question

Can heart-rate variability measured before repeated sprint sets identify the onset of physical fatigue during a sprint interval exercise test in trained cyclists?

Summary

Well-trained mountain-bike cyclists completed an acute laboratory sprint interval exercise test: four sets of four 30-second maximal cycling sprints with long recoveries between sets. Heart-rate variability fell as more sprint sets accumulated, but it did not track average or peak power fatigue well, so HRV was not a good acute fatigue marker for this protocol.

Methodology

  • 27 well-trained mountain-bike cyclists.
  • 27 participants.
  • Cycle ergometer.
  • Work intervals: 30 s maximal sprint.
  • Recovery: 90 s low-intensity cycling; 25-40 min between sets.
  • Intensity: Maximal sprinting at 0.8 Nm/kg fixed torque.
  • Several hours including long recoveries.
  • Single acute test.
  • Single day.
  • Acute repeated-measures laboratory study
  • Heart-rate variability, Power output, and Metabolic markers were tracked.

Outcomes

HRV

HRV indexes declined as repeated sprint sets accumulated.

RRNN, SDNN, and VLF decreased in set 2; all time/frequency indexes decreased in sets 3 and 4 versus set 1.

Safety concern

Power

Peak power fell earlier than average power.

Ppeak decreased in sets 2-4; Pavg decreased only in set 4.

Mixed

HRV-fatigue link

HRV did not correlate with power-output fatigue.

No significant correlations between HRV changes and Pavg or Ppeak changes.

No clear change

Metabolic markers

Oxygen uptake increased and hydrogen concentration decreased by set 4; lactate did not significantly change.

VO2tou increased in set 4; H+ decreased in set 4; La- p=0.176.

Mixed

Insights

  • HRV can reflect accumulated autonomic stress but not necessarily acute sprint fatigue.
  • Power-output tracking is more relevant than HRV for deciding whether maximal sprint quality is falling.
  • This protocol is athlete/lab-specific and not a general consumer HIIT template.

Limitations

  • Acute-only study.
  • No control group.
  • Well-trained cyclist sample.
  • Outliers removed before correlation analysis.
  • Safety reporting not detailed.

Safety

  • Adverse events and injuries were not reported.
  • Between-set recovery was extended until blood pH returned to at least 7.35.