# Sex Differences in Heart Rate Variability and Vascular Function Following High-Intensity Interval Training in Young Adults

PMID: 38380301
Journal: Journal of human kinetics
Published: 2023-10-11
Authors: Seo MW, Park TY, Jung H

## Question

Do physically active young adult males and females differ in heart-rate variability and vascular function responses after a single bout of cycling HIIT?

## Summary

This acute laboratory study compared how healthy physically active young men and women responded during recovery from a single cycling HIIT session. Participants completed 10 rounds of 20 seconds hard cycling at 115-130% Wmax with 100 seconds recovery, after a 5-minute warm-up. Heart-rate variability recovered more slowly in women than men during the first 15 minutes after HIIT, while blood pressure and brachial-ankle pulse wave velocity responses did not differ significantly by sex.

## Population

- Healthy physically active young adults, 12 male and 12 female.
- Sample size: 24
- Age: 19.5 +/- 0.2 years overall; inclusion age 19-25 years.
- Sex: 12 male and 12 female.
- Fitness level: Physically active, with more than 150 minutes per week of moderate-to-vigorous physical activity.
- Health status: Healthy, normal-BMI adults with no general disease, relevant medication, or musculoskeletal injuries.

## Methodology

- Acute repeated-measures comparison of male and female participants after a single supervised HIIT session.
- Two visits plus seven-day physical activity monitoring; acute recovery outcomes measured for 65 minutes after one HIIT session.
- Laboratory setting with cycle ergometry, HRV measurement, and vascular screening.
- Controlled study design.

## Protocol

- Single-bout cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 20 seconds at 115-130% Wmax.
- Recovery: 100 seconds at 60 RPM without resistance.
- Sets or repetitions: 10 bouts.
- Intensity: 115-130% Wmax; applied resistance reported as 3 kp for males and 2 kp for females.
- Session duration: 20-minute HIIT program, after at least 5 minutes warm-up.
- Frequency: Single acute session.
- Program length: One session.
- Progression: None.
- Between-sex comparison under same HIIT protocol.
- Modality: Cycle ergometer.
- Work intervals: 20 seconds at 115-130% Wmax.
- Recovery: 100 seconds at 60 RPM without resistance.
- Sets or repetitions: 10 bouts.
- Intensity: Same relative Wmax target; male applied resistance 3 kp and female applied resistance 2 kp.
- Session duration: 20-minute HIIT program, after at least 5 minutes warm-up.
- Frequency: Single acute session.
- Program length: One session.
- Progression: None.

## Outcomes

### HRV time-domain recovery
Status: mixed
Male participants recovered faster than female participants for R-R interval, rMSSD, and SDNN by 15 minutes after HIIT.

Sex-by-time interactions were significant for HR, R-R interval, rMSSD, and SDNN; females had lower rMSSD and SDNN than males at 15 minutes after HIIT (p < 0.05).

### HRV frequency-domain response
Status: mixed
Females showed higher LF/HF immediately after HIIT, while males had higher LF/HF at baseline; LF and HF values differed between sexes immediately and 15 minutes after exercise.

Significant sex-by-time interactions were reported for ln LF, ln HF, and ln LF/HF; immediate post-exercise LF/HF was higher in females than males (Cohen's d = 0.98, p < 0.05).

### Blood pressure and arterial stiffness
Status: no clear change
No significant sex-by-time interactions were observed for bilateral blood pressure or brachial-ankle pulse wave velocity variables.

The article reports no significant interactions between sexes by time for all blood pressure and ba-PWV variables.

## Practical Insights

- Short-interval cycling HIIT can acutely perturb HRV for at least 15 minutes, and recovery patterns may differ by sex in young active adults.
- Blood pressure and arterial stiffness responses to this single session did not show sex-specific differences.
- This paper is more useful for recovery monitoring and physiology context than for claims about long-term HIIT training benefits.

## Limitations

- Small sample size.
- Acute-only design with one HIIT session.
- No randomization and no non-exercise control group.
- Only healthy, normal-BMI, physically active young adults were studied.
- Sex hormones and other biochemical variables were not measured.

## Safety And Adherence

- Adverse events were not explicitly reported in the extracted text.
- Participants were screened healthy young adults with normal BMI and no disease, medication, or musculoskeletal injury history.
- A certified strength and conditioning specialist supervised all HIIT procedures.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/38380301/) (pubmed)
- [DOI](https://doi.org/10.5114/jhk/170964) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10875700/) (full text)

## Agent Guidance

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