# Hypoxic repeated sprint interval training improves cardiorespiratory fitness in sedentary young women

PMID: 35154334
Journal: Journal of exercise science and fitness
Published: 2022 Apr
Authors: Kong Z, Lei OK, Sun S, Li L, Shi Q, Zhang H, Nie J

## Question

Does repeated sprint interval training performed in normoxia or simulated hypoxia improve cardiorespiratory fitness and cardiometabolic markers in sedentary young women?

## Summary

In sedentary young women, 4 weeks of supervised cycling repeated sprint interval training improved VO2peak when performed under simulated hypoxia. Body composition, fasting glucose, and lipid measures did not change.

## Population

- Sedentary young women randomized to normoxic RSIT, two hypoxic RSIT conditions, or non-exercise control
- Sample size: 62
- Age: 21.9 +/- 2.8 years
- Sex: 62 women
- Fitness level: Sedentary; baseline VO2peak 25.9 +/- 4.5 mL/kg/min
- Health status: Good health, non-smokers, regular menstrual cycles, no cardiovascular or associated disease

## Methodology

- Randomized controlled parallel-group training study
- 4 weeks
- Supervised laboratory cycling with gas-control masks
- Randomized and controlled study design.

## Protocol

- Repeated sprint interval training in hypoxia or normoxia.
- Modality: Cycle ergometer repeated sprint interval training.
- Work intervals: 6 s maximal/all-out cycling.
- Recovery: 9 s recovery.
- Sets or repetitions: 80 repetitions per session.
- Intensity: Maximal/all-out sprints; hypoxia groups trained at FiO2 0.155 or progressively 0.155 to 0.135.
- Session duration: About 20 min plus 10 min pre-exposure, 5 min warm-up, and 5 min cool-down.
- Frequency: 3 sessions/week.
- Program length: 4 weeks; 12 sessions.
- Progression: Resistance increased by 0.5 kg when all sprint bouts were maintained above 100 rpm for 2 consecutive sessions, up to 5% body mass; incremental hypoxia group reduced FiO2 weekly.
- Non-exercise control and normoxic RSIT.
- Modality: No exercise control; normoxic cycling RSIT with FiO2 0.209.
- Work intervals: Same RSIT work interval for normoxic exercise comparator.
- Recovery: Same 9 s recovery for normoxic exercise comparator.
- Sets or repetitions: 80 repetitions for normoxic exercise comparator.
- Intensity: Normoxic all-out cycling or no exercise.
- Session duration: Same training duration for normoxic exercise comparator.
- Frequency: 3 sessions/week for normoxic exercise comparator.
- Program length: 4 weeks.
- Progression: Same resistance progression for normoxic exercise comparator.

## Outcomes

### VO2peak
Status: improved
VO2peak improved in both hypoxic training groups and was higher than normoxic training.

H2500 +8.2%, p < 0.001, d = 0.52; H2500-3400 +10.9%, p < 0.05, d = 0.99; hypoxic groups greater than normoxic training p < 0.05

### Normoxic VO2peak
Status: no clear change
Normoxic RSIT showed a smaller, non-significant VO2peak change.

Normoxic group +3.6%, not significant

### Metabolic markers
Status: no clear change
Body composition, fasting glucose, and lipid markers did not change.

No significant changes reported across groups

### Safety
Status: no clear change
The training was reported as well tolerated with no adverse events.

Exceptional completion rate; no adverse events reported

## Practical Insights

- A very dense 6 s/9 s sprint design can be completed by sedentary young women under close supervision.
- Simulated hypoxia appeared to amplify VO2peak gains over the same normoxic sprint dose.
- The equipment and hypoxic exposure requirements limit direct translation to a general mobile HIIT product.

## Limitations

- Short 4-week intervention
- Women only and young sedentary sample
- Hypoxic equipment and laboratory supervision reduce generalizability
- No hemoglobin or hematocrit assessment
- High-volume 80-sprint format may be difficult to sustain outside a lab

## Safety And Adherence

- No adverse events were reported; heart rate and SpO2 were monitored before and after each sprint.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35154334/) (pubmed)
- [DOI](https://doi.org/10.1016/j.jesf.2022.01.005) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8819388/) (full text)

## Agent Guidance

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