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

PMID: 39066154
Journal: Sensors (Basel, Switzerland)
Published: 2024 Jul 22
Authors: 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.

## Population

- 13 healthy physically active young male adults completed three cycle HIIT protocols.
- Sample size: 13
- Age: 19.4 +/- 0.3 years
- Sex: Male
- Fitness level: Physically active
- Health status: Normal BMI and no relevant disease, medication, or neuroskeletal injury

## Methodology

- Randomized counter-balanced crossover acute trial
- Three acute sessions separated by 7 days
- Cycle ergometer laboratory testing
- Randomized and controlled study design.

## Protocol

- 40 s/200 s cycle HIIT.
- Modality: Cycle ergometer.
- Work intervals: 40 s.
- Recovery: 200 s pedaling without resistance at 60 rpm.
- Sets or repetitions: 5 sets.
- Intensity: 115-130% Wmax.
- Session duration: 20 min interval block plus at least 5 min warm-up.
- Frequency: Single acute session in crossover.
- Program length: One session per protocol.
- Progression: None.
- Shorter matched HIIT protocols.
- Modality: Cycle ergometer.
- Work intervals: 10 s or 20 s.
- Recovery: 50 s or 100 s pedaling without resistance at 60 rpm.
- Sets or repetitions: 20 sets of 10/50 or 10 sets of 20/100.
- Intensity: 115-130% Wmax.
- Session duration: 20 min interval block plus at least 5 min warm-up.
- Frequency: Single acute session per protocol.
- Program length: One session per protocol.
- Progression: None.

## Outcomes

### HRV
Status: mixed
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.

### Ankle SBP
Status: improved
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.

### RPE
Status: worse/safety concern
The longest work-interval protocol felt harder.

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

## Practical 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 And Adherence

- 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.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/39066154/) (pubmed)
- [DOI](https://doi.org/10.3390/s24144758) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11280837/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.