# High-Intensity Interval Training in Normobaric Hypoxia Leads to Greater Body Fat Loss in Overweight/Obese Women than High-Intensity Interval Training in Normoxia

PMID: 29472870
Journal: Frontiers in Physiology
Published: 2018 Feb 7
Authors: Camacho-Cardenosa A, Camacho-Cardenosa M, Burtscher M, Martínez-Guardado I, Timon R, Brazo-Sayavera J, Olcina G

## Question

Does adding normobaric hypoxia to two types of cycling HIIT improve body-composition and substrate-oxidation outcomes in overweight or obese women?

## Summary

This randomized double-blind study tested cycling HIIT in normoxia or simulated altitude in sedentary overweight/obese premenopausal women. Hypoxia plus HIIT produced greater fat-loss and muscle-mass signals than normoxia, but dropout was high and group-count reporting was inconsistent.

## Population

- Sedentary premenopausal overweight/obese women
- Sample size: 59
- Sex: Women
- Fitness level: Sedentary
- Health status: Overweight/obese without associated diseases

## Methodology

- Randomized double-blind four-group intervention study
- 12 weeks
- Supervised cycle ergometer sessions in normobaric hypoxia or normoxia
- Randomized and controlled study design.

## Protocol

- Cycle AIT/SIT in hypoxia or normoxia.
- Modality: Cycle ergometer.
- Work intervals: AIT 3 minutes; SIT 30 seconds.
- Recovery: 3 minutes active recovery.
- Sets or repetitions: 3 to 6 intervals.
- Intensity: AIT 90% Wmax; SIT 130% Wmax; recovery 55-65% Wmax.
- Session duration: AIT up to 41.5 minutes; SIT up to 29.62 minutes.
- Frequency: 3 sessions/week.
- Program length: 12 weeks.
- Progression: Intervals increased from 3 to 6.
- Normoxia or alternate interval comparator.
- Modality: Cycle ergometer.
- Work intervals: Matched within AIT or SIT comparison.
- Recovery: 3 minutes active recovery.
- Sets or repetitions: 3 to 6 intervals.
- Intensity: Same workload prescription in normoxia.
- Session duration: Matched by protocol type.
- Frequency: 3 sessions/week.
- Program length: 12 weeks.
- Progression: Intervals increased from 3 to 6.

## Outcomes

### Fat mass
Status: improved
Hypoxia groups lost more fat mass than normoxia counterparts.

SitH lower than SitN T1-T3 and T1-T4 p<0.05; AitH decreased vs AitN T1-T4 p<0.01.

### Muscle mass
Status: improved
Muscle mass increased significantly in hypoxia groups.

AitH vs AitN T1-T4 p=0.022; SitH increased T1-T4 p<0.05.

### Body fat percent
Status: improved
All groups decreased body fat percentage, with significant reductions in hypoxia groups.

### Safety physiology
Status: mixed
Hypoxia lowered oxygen saturation; HR and power were not significantly different.

SpO2 lower p<0.01.

## Practical Insights

- Hypoxia findings are not directly transferable to normal-air HIIT.
- Progressive interval counts can be a useful programming structure.

## Limitations

- High dropout.
- Diet and physical activity registered only twice.
- No nonexercise control group.
- Group count inconsistency.
- Special equipment required.

## Safety And Adherence

- No serious health problems were reported.
- Twenty-three participants dropped out, reportedly due to health problems not related to the protocol, occupational factors, or personal problems.
- Participants were screened for exercise contraindications and monitored with SpO2, HR, RPE, and supervision.
- Group sample counts were inconsistent across article sections, creating uncertainty in exact final group sizes.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/29472870/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2018.00060) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5810257/) (full text)

## Agent Guidance

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