# Nitrate Intake Promotes Shift in Muscle Fiber Type Composition during Sprint Interval Training in Hypoxia

PMID: 27378942
Journal: Frontiers in Physiology
Published: 2016-06-14
Authors: De Smet S, Van Thienen R, Deldicque L, James R, Sale C, Bishop DJ, Hespel P

## Question

Does sprint interval training in hypoxia, alone or with nitrate supplementation, produce greater muscle and performance adaptations than normoxic sprint interval training?

## Summary

Recreationally active men completed five weeks of cycling sprint interval training in normoxia or hypoxia, with or without nitrate supplementation. Fitness improved similarly across groups, while nitrate plus hypoxic SIT uniquely increased the proportion of type IIa muscle fibers; one eligible participant stopped because of SIT intolerance.

## Population

- Healthy recreationally active men recruited from KU Leuven.
- Sample size: 27
- Sex: Men only
- Fitness level: Recreationally active, not competitive.
- Health status: Healthy, non-smokers, no medication or supplements.

## Methodology

- Matched-group training experiment
- 5 weeks
- KU Leuven laboratory cycle-ergometer training
- Randomized and controlled study design.

## Protocol

- Hypoxic SIT plus nitrate.
- Modality: Cycle ergometer.
- Work intervals: 30-s maximal sprint.
- Recovery: 4.5-min active recovery at 50 W.
- Sets or repetitions: 4-6 sprints.
- Intensity: Maximal sprinting in FiO2 15.0%; nitrate 6.45 mmol 3 h before sessions.
- Session duration: 30-40 min including warm-up and cool-down.
- Frequency: 3 sessions/week.
- Program length: 5 weeks.
- Progression: 4 sprints weeks 1-2, 5 weeks 3-4, 6 week 5.
- Normoxic or hypoxic SIT plus placebo.
- Modality: Cycle ergometer.
- Work intervals: 30-s maximal sprint.
- Recovery: 4.5-min active recovery at 50 W.
- Sets or repetitions: 4-6 sprints.
- Intensity: Normoxia FiO2 20.9% or hypoxia FiO2 15.0% with placebo.
- Session duration: 30-40 min including warm-up and cool-down.
- Frequency: 3 sessions/week.
- Program length: 5 weeks.
- Progression: Same sprint-count progression as intervention.

## Outcomes

### VO2max
Status: improved
VO2max improved similarly in all three SIT groups.

Training effect p<0.05; no clear between-group advantage.

### Type IIa fibers
Status: improved
Type IIa fiber proportion increased only with hypoxic SIT plus nitrate.

HN 45% to 56%, p<0.05; higher than H post-training.

### Buffering capacity
Status: no clear change
Muscle buffering capacity did not significantly change.

### Tolerability
Status: mixed
Most completed training, but one eligible participant stopped due to SIT intolerance.

27/30 eligible participants completed.

## Practical Insights

- Thirty-second all-out sprints require long recovery and may not be tolerated by everyone.
- Hypoxia did not add clear endurance benefits compared with normoxic SIT.

## Limitations

- Small male-only sample.
- No nitrate-only normoxic group.
- Specialized hypoxia and supplement conditions.
- Short intervention.

## Safety And Adherence

- One eligible participant did not complete the study because of SIT intolerance.
- Hypoxic sessions produced low oxygen saturation during SIT, with reported group averages around 85-87% in the final week.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/27378942/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2016.00233) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4906611/) (full text)

## Agent Guidance

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