# Heart Rate and Oxygen Uptake During Recovery from High-Intensity Interval Training: A Retrospective Analysis

PMID: 40724066
Journal: International Journal of Environmental Research and Public Health
Published: 2025-06-25
Authors: Astorino TA, Bogdanis GC, Costa EC

## Question

How do heart rate and oxygen uptake during active recovery compare with work intervals across low-volume cycling HIIT protocols?

## Summary

This retrospective pooled analysis found that active recovery periods during short cycling HIIT maintained heart rate and oxygen uptake at levels similar to the work intervals. Recovery periods therefore contributed substantial cardiovascular load rather than being physiologically idle.

## Population

- Healthy physically active adults
- Sample size: 104
- Age: 24 +/- 5 years
- Sex: Men and women
- Fitness level: Physically active, mean VO2max 40 +/- 7 mL/kg/min
- Health status: Healthy, non-obese, nonsmoking

## Methodology

- Retrospective pooled analysis of prior within-subject cycling HIIT studies
- Single-session data pooled from seven prior studies
- Laboratory cycling studies
- Controlled study design.

## Protocol

- Cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 30 to 60 s.
- Recovery: 10 to 75 s active recovery.
- Sets or repetitions: Varied.
- Intensity: 70-85% Wmax; peak HR about 90.7% HRmax.
- Session duration: Varied.
- Frequency: Single-session data.
- Program length: Retrospective acute analysis.
- Progression: Not applicable.
- Active recovery periods.
- Modality: Cycle ergometer.
- Recovery: 10 to 75 s active recovery.
- Sets or repetitions: Within-session recovery intervals.
- Intensity: Low-intensity active recovery, exact workload varied.
- Session duration: Within HIIT sessions.
- Frequency: Within-session comparison.
- Program length: Acute analysis.
- Progression: Not applicable.

## Outcomes

### Heart rate
Status: no clear change
Mean heart rate was similar during exercise and active recovery intervals.

159 +/- 14 versus 160 +/- 15 bpm, p=0.48.

### Oxygen uptake
Status: no clear change
Mean oxygen uptake was similar during exercise and active recovery intervals.

1.97 +/- 0.47 versus 1.98 +/- 0.48 L/min, p=0.82.

### Fitness strata
Status: mixed
Lower-fitness participants reached higher percentages of VO2max than fitter participants.

Example strata: fit men 66.5% VO2max versus lower-fitness women 86.8% VO2max.

## Practical Insights

- Short active recovery can remain a high cardiovascular-load period.
- Rest design should be included in total HIIT dose decisions.
- Lower-fitness users may need easier or longer recovery even when work intervals are the same.

## Limitations

- Retrospective pooled analysis
- Different original protocols
- Healthy active young adults
- Cycling only
- Active recovery only

## Safety And Adherence

- No adverse-event or adherence outcomes were reported in the retrospective analysis.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/40724066/) (pubmed)
- [DOI](https://doi.org/10.3390/ijerph22070999) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12294763/) (full text)

## Agent Guidance

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