PMID 39066154

Research
All papers

Acute Response of Different High-Intensity Interval Training Protocols on Cardiac Auto-Regulation Using Wearable Device

Seo MW

Question

Do HIIT protocols with identical total work, intensity, and work-rest ratio but different interval lengths produce different acute HRV and vascular-function responses?

Summary

In 13 physically active young men, three cycle HIIT sessions with the same 1:5 work-rest ratio and total work produced different acute cardiac-autoregulation responses. The longest work interval, 40 s with 200 s recovery, produced the strongest HRV and ankle blood-pressure responses but also higher peak heart rate and RPE.

Methodology

  • 13 healthy physically active young male adults completed three cycle HIIT protocols.
  • 13 participants.
  • Cycle ergometer.
  • Work intervals: 40 s.
  • Recovery: 200 s pedaling without resistance at 60 rpm.
  • Intensity: 115-130% Wmax.
  • 20 min interval block plus at least 5 min warm-up.
  • Single acute session in crossover.
  • One session per protocol.
  • Randomized counter-balanced crossover acute trial
  • Heart-rate variability, Vascular function, and RPE were tracked.

Outcomes

HRV

40/200 produced stronger acute HRV frequency-domain responses than shorter intervals.

Significant group x time effects for ln LF, ln HF, and ln LF/HF; 40/200 differed immediately and at 15 min.

Mixed

Ankle SBP

Postexercise hypotension in bilateral ankle area was seen only after 40/200.

Conclusion reported right -12.2% and left -12.6% at 5 min after 40/200.

Improved

RPE

The longest work-interval protocol felt harder.

40/200 RPE was higher than 10/50 and 20/100, p<0.001.

Safety concern

Insights

  • Equal work-rest ratio and total work do not make HIIT sessions physiologically equivalent.
  • Longer bouts can increase autonomic/vascular stimulus but also perceived exertion.
  • Use Wmax-based protocols only when testing and supervision are available.

Limitations

  • Small sample.
  • Male young active participants only.
  • Acute surrogate outcomes.
  • HRV and vascular follow-up lasted about 1 hour only.
  • No immediate vascular test.

Safety

  • No adverse events were reported.
  • A pilot protocol of five 40 s bouts at 130-150% Wmax was not completed due to exhaustion.
  • Participants were healthy, normal-BMI, physically active young men.