# Effects of high-intensity interval training and sprint interval training on cardiac autonomic modulation and cardiorespiratory fitness in healthy women

PMID: 36232163
Journal: International Journal of Environmental Research and Public Health
Published: 2022 Oct 8
Authors: Oliveira J, Gentil P, Naves JP, Souza Filho LF, Silva L, Zamunér AR, de Lira CA, Rebelo A

## Question

Do 8 weeks of HIIT and SIT differ in effects on cardiac autonomic modulation, heart-rate kinetics, and cardiorespiratory fitness in healthy women?

## Summary

In healthy physically active women, 8 weeks of supervised cycling HIIT or SIT improved cardiorespiratory conditioning and several heart-rate-variability measures. Traditional HRV and VO2 outcomes did not show a clear overall group-by-time advantage, but nonlinear HRV indices suggested better sympathovagal balance after the higher-volume HIIT protocol.

## Population

- Healthy physically active women randomized to HIIT or SIT.
- Sample size: 59
- Age: 29.96 +/- 6.25 years
- Sex: Female
- Fitness level: Physically active, about 150 minutes per week
- Health status: Healthy; excluded BMI >=30 and major cardiometabolic, pulmonary, renal, neoplastic, stroke, or musculoskeletal conditions

## Methodology

- Randomized clinical trial
- 8 weeks
- Supervised morning cycle-ergometer sessions three days per week
- Randomized and controlled study design.

## Protocol

- Cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 4 minutes.
- Recovery: 3 minutes active recovery.
- Sets or repetitions: 4 intervals.
- Intensity: 90-95% HRpeak/critical frequency for work bouts; 50-60% HRpeak during active recovery.
- Session duration: About 33 minutes including warm-up.
- Frequency: 3 sessions per week.
- Program length: 8 weeks; 24 sessions.
- Progression: Load adjusted during sessions if HR moved outside target range.
- Cycling SIT.
- Modality: Cycle ergometer.
- Work intervals: 30 seconds.
- Recovery: 4 minutes passive or unloaded light cycling.
- Sets or repetitions: 4 maximum efforts.
- Intensity: Maximum sprint effort.
- Session duration: About 23 minutes including warm-up.
- Frequency: 3 sessions per week.
- Program length: 8 weeks; 24 sessions.
- Progression: No major progression reported.

## Outcomes

### VO2
Status: improved
VO2 improved over time across groups.

VO2 time effect F=8.993, p=0.004; group effect F=12.523, p=0.001; no significant group x time interaction reported for usual VO2 variables.

### Traditional HRV
Status: improved
Several traditional HRV measures improved over time across groups.

Time effects: RMSSD p=0.002, SDNN p=0.003, SD1 p=0.003, SD2 p=0.011; effects remained after VO2peak adjustment.

### Nonlinear HRV
Status: mixed
Nonlinear HRV interactions favored HIIT on selected indices.

Group x time: ES F=6.87, p=0.011; EC F=5.42, p=0.023; 2LV p=0.026; HIIT better than SIT at post for 0V p=0.022, ES p=0.004, EC p=0.025.

### Retention
Status: mixed
A substantial minority of randomized participants abandoned the study.

43 of 59 randomized participants completed; 16 abandoned due to health problems n=2, time availability n=9, and no reason n=5.

## Practical Insights

- Both 4x4-minute HIIT and 4x30-second SIT cycling formats can improve fitness/autonomic outcomes in healthy women.
- Higher-volume HIIT may be more favorable for selected nonlinear HRV markers than lower-volume SIT.
- Time availability was the largest abandonment reason, so session length and scheduling matter.

## Limitations

- Final analyzed sample was 43 after 16 abandonments.
- Healthy physically active women only.
- No non-exercise control group.
- Adverse events were monitored but not clearly summarized in results.
- Authors called for probabilistic sampling and other populations.

## Safety And Adherence

- The protocol included monitoring for dizziness, nausea, muscle pain, and other adverse events.
- Sixteen participants abandoned the study; two cited health problems.
- No detailed adverse-event summary was identified in the results sections extracted.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/36232163/) (pubmed)
- [DOI](https://doi.org/10.3390/ijerph191912863) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9566246/) (full text)

## Agent Guidance

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