# The impact of sprint interval training with or without weight loss on substrate oxidation in adults: A secondary analysis of the i-FLEX study

PMID: 37144609
Journal: Physiological Reports
Published: 2023
Authors: Nancekievill D, Colpitts BH, Seaman K, Girard M, Sénéchal M

## Question

Does sprint interval training change resting and submaximal substrate oxidation differently in adults who lose weight versus those who do not?

## Summary

In adults completing 4 weeks of supervised cycling sprint interval training, those who lost any weight showed improved submaximal fat oxidation and lower exercise RER. Resting substrate oxidation did not change, and the weight-loss subgroup differed by sex and work volume.

## Population

- Adults from the i-FLEX study grouped after training by whether body weight decreased
- Sample size: 34
- Age: 19-60 years
- Sex: 15 men and 19 women
- Fitness level: Adults able to complete SIT; prior training experience not recorded
- Health status: Excluded diabetes/impaired glucose and medications or programs affecting weight or insulin/carbohydrate metabolism

## Methodology

- Secondary analysis of a supervised sprint interval training intervention
- 4 weeks
- University laboratory supervised cycling sessions
- Controlled study design.

## Protocol

- Four-week Wingate-style cycling SIT.
- Modality: Cycle ergometer.
- Work intervals: 30 s.
- Recovery: 4 min active recovery at minimum wattage.
- Sets or repetitions: Week 1: 2 intervals; week 2: 3; weeks 3-4: 4.
- Intensity: Wingate sprints at 7.5% body weight.
- Session duration: 4 min warm-up, sprint/recovery intervals, 5 min cool-down.
- Frequency: 3 sessions/week.
- Program length: 4 weeks.
- Progression: Interval count increased from 2 to 4 per session.
- Post hoc non-weight-loss subgroup.
- Modality: Same SIT protocol.
- Work intervals: 30 s.
- Recovery: 4 min active recovery.
- Sets or repetitions: Same progression.
- Intensity: Same Wingate prescription.
- Session duration: Same session structure.
- Frequency: 3 sessions/week.
- Program length: 4 weeks.
- Progression: Same progression.

## Outcomes

### Submax fat oxidation
Status: improved
The weight-loss subgroup increased submaximal fat oxidation.

WL 0.117 +/- 0.224 to 0.249 +/- 0.165 g/min, p = 0.008; group difference p = 0.005; interaction retained after covariate adjustment

### Submax RER
Status: improved
Exercise RER fell in the weight-loss subgroup, although the adjusted interaction was weaker.

WL 0.96 +/- 0.08 to 0.92 +/- 0.06, p = 0.030; group difference p = 0.017; adjusted interaction p = 0.081

### Resting oxidation
Status: no clear change
Resting substrate oxidation did not differ meaningfully by weight-loss response.

No significant resting substrate oxidation differences reported

### Training work
Status: mixed
Weight-loss participants completed higher work volume and had higher relative power.

Work volume 65,267 vs 47,062 kgm, p < 0.001; relative peak power p = 0.039; relative mean power p = 0.018

## Practical Insights

- Submaximal substrate changes after SIT may depend on weight change, sex distribution, and total work performed.
- Resting metabolism outcomes should not be inferred from submaximal exercise oxidation.
- Tracking training work volume may help explain heterogeneous responses.

## Limitations

- Secondary analysis with post hoc weight-loss grouping
- Small sample
- Weight-loss group was mostly male and non-weight-loss group mostly female
- Baseline and post tests were not time-of-day matched
- Prior training experience was not recorded

## Safety And Adherence

- Sessions were supervised one-on-one; the article did not clearly report adverse-event counts.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/37144609/) (pubmed)
- [DOI](https://doi.org/10.14814/phy2.15684) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10161214/) (full text)

## Agent Guidance

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