# High-Intensity Interval Training in Normobaric Hypoxia Improves Cardiorespiratory Fitness in Overweight Chinese Young Women

PMID: 28386234
Journal: Frontiers in Physiology
Published: 2017 Mar 23
Authors: Kong Z, Shi Q, Nie J, Tong TK, Song L, Yi L, Hu Y

## Question

Does performing a 5-week low-volume cycling HIIT program in normobaric hypoxia improve cardiometabolic and body composition outcomes more than the same HIIT under normoxia in overweight Chinese young women?

## Summary

In sedentary overweight Chinese young women, 5 weeks of cycling HIIT improved cardiorespiratory fitness and some lipid ratios. Performing the same HIIT under mild normobaric hypoxia produced larger gains in VO2peak and peak oxygen pulse than normoxia, but did not add benefits for body composition, fasting leptin, or serum lipids. A physician attended all tests and training sessions.

## Population

- Twenty-four sedentary overweight otherwise healthy Chinese young women completing normoxic or normobaric hypoxic cycling HIIT.
- Sample size: 24
- Age: Eligible age 18-30 years.
- Sex: All female.
- Fitness level: Sedentary; baseline VO2peak about 32-34 mL/kg/min.
- Health status: Overweight with body fat >=30%; otherwise healthy.

## Methodology

- Double-blind randomized placebo-controlled training study comparing normoxic versus normobaric hypoxic HIIT.
- 5 weeks of HIIT, 4 sessions/week.
- 100 m2 hypoxic laboratory at Beijing Sport University; outcome tests before and after intervention.
- Randomized and controlled study design.

## Protocol

- Hypoxic cycling HIIT.
- Modality: Cycle ergometer in normobaric hypoxia.
- Work intervals: 8 s maximal cycling effort.
- Recovery: 12 s recovery with pedal frequency 20-30 rpm.
- Sets or repetitions: 60 repetitions.
- Intensity: Maximal efforts; FIO2 0.15; about 84-88% HRmax during training.
- Session duration: 20 min protocol plus warm-up/cool-down.
- Frequency: 4 sessions/week.
- Program length: 5 weeks.
- Progression: Initial 1 kp load; +0.5 kp when full protocol was consistently completed or HR decreased at same workload.
- Normoxic cycling HIIT.
- Modality: Cycle ergometer under normal oxygen.
- Work intervals: 8 s maximal cycling effort.
- Recovery: 12 s recovery.
- Sets or repetitions: 60 repetitions.
- Intensity: Same protocol under FIO2 0.21.
- Session duration: 20 min protocol plus warm-up/cool-down.
- Frequency: 4 sessions/week.
- Program length: 5 weeks.
- Progression: Same workload progression.

## Outcomes

### VO2peak
Status: improved
Both groups improved VO2peak, with larger gains under hypoxia.

VO2peak L/min time effect p<0.001, time x group p=0.041; NORM +11.8%, HYP +26.1% in abstract.

### Peak oxygen pulse
Status: improved
Peak oxygen pulse improved more in hypoxia than normoxia.

Time effect p<0.001; group effect p=0.024; time x group p=0.022.

### Serum lipid ratios
Status: improved
TC/HDL-C and TG/HDL-C ratios improved over time, but hypoxia did not add a significant lipid benefit.

TC/HDL-C time effect p=0.035; TG/HDL-C time effect p=0.027; no significant group effects.

### Body composition and leptin
Status: no clear change
Weight, BMI, lean mass, fat mass, body fat percentage, regional composition, and fasting leptin did not significantly change.

Table 3 reports non-significant time and group x time effects for body composition and leptin.

## Practical Insights

- Very short cycling intervals can improve fitness quickly in sedentary overweight young women.
- Hypoxia may increase VO2peak gains in a lab setting, but it did not improve body composition or serum lipids beyond normoxic HIIT.
- Hypoxic HIIT needs oxygen saturation monitoring and medical supervision.

## Limitations

- Small sample size.
- Only young Chinese women.
- Dietary intake and activity were self-reported and sampled 3 days/week.
- Short 5-week intervention.
- Hypoxic stress appeared to attenuate over time.
- Hypoxic chamber setting limits practical translation.

## Safety And Adherence

- A physician attended all tests and training sessions.
- HR and SpO2 were monitored before, during, and after HIIT.
- No specific adverse events were reported in the extracted main text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/28386234/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2017.00175) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5362639/) (full text)

## Agent Guidance

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