# Influence of 4-week lower extremity high-intensity interval training on energy metabolism and maximal oxygen uptake of elite swimmers

PMID: 40755811
Journal: PeerJ
Published: 2025-07-31
Authors: Jin R, Sun J, Jiang N, Chen C

## Question

Does a 4-week dry-land lower-limb HIIT program improve energy metabolism and VO2max in elite swimmers compared with regular training?

## Summary

In elite swimmers, 4 weeks of supervised dry-land lower-limb HIIT improved absolute phosphagen, glycolytic, aerobic, and total energy supply and VO2max compared with regular training alone. The sample was small and limited to elite swimmers from one institution.

## Population

- Elite competitive swimmers from Shanghai University of Sport.
- Sample size: 24
- Age: HIIT 19.94 ± 1.4 years; control 21.17 ± 1.6 years.
- Sex: Each group included 8 males and 4 females.
- Fitness level: Elite swimmers with at least 10 years of competitive swimming experience.
- Health status: No injury or illness in previous 6 months; no chronic disease, recent surgery, cardiovascular risk, or performance-enhancing substance use.

## Methodology

- Randomized controlled pre/post intervention.
- 4 weeks
- Physical Training Research Center of Shanghai University of Sport.
- Randomized and controlled study design.

## Protocol

- Lower-limb dry-land HIIT.
- Modality: Dry-land lower-limb circuit including high leg lift, elastic band drills, BOSU squat jumps, squat jumps, slide board, side jumps, and resisted jumps.
- Work intervals: 20 seconds.
- Recovery: 10 seconds.
- Sets or repetitions: Eight exercises per circuit, three circuits, two sets per session.
- Intensity: Maximal intensity for each exercise.
- Session duration: About 60 minutes including 20-minute warm-up, 30-minute HIIT work, and 10-minute stretching/relaxation.
- Frequency: 3 sessions per week.
- Program length: 4 weeks.
- Progression: No explicit load progression beyond the 4-week repeated circuit; protocol was standardized.
- Regular training.
- Modality: Usual swimmer training regimen.
- Program length: 4 weeks.
- Progression: No added lower-limb HIIT.

## Outcomes

### Energy supply
Status: improved
HIIT significantly increased absolute phosphagen, glycolytic, aerobic, and total energy supply while controls did not.

HIIT total energy supply 214.48 ± 38.58 to 290.65 ± 42.01 kJ; group × time F = 101.979, p < 0.001, η2 = 0.823.

### Energy proportions
Status: no clear change
Relative contribution percentages of energy pathways did not significantly change.

Phosphagen %, glycolytic %, anaerobic %, and aerobic % all p > 0.05.

### VO2max
Status: improved
VO2max improved in the HIIT group and did not improve in controls.

HIIT 51.48 ± 3.85 to 55.03 ± 4.90 ml/min/kg; time p = 0.041; group p = 0.009; time × group p < 0.001.

## Practical Insights

- A short dry-land lower-limb HIIT block may improve metabolic output and VO2max in already highly trained swimmers.
- The 20:10 structure is highly specific and supervised; it should not be treated as general home-fitness evidence.
- The study supports sport-specific lower-limb power programming more than general public HIIT guidance.

## Limitations

- Small sample from one institution.
- Elite swimmers only.
- Menstrual cycle phase of female athletes was not monitored or controlled.
- Neuromuscular activity and lactate clearance mechanisms were not directly measured.
- Performance outcomes in the pool were not reported.

## Safety And Adherence

- One screened athlete was excluded due to injury risk before enrollment.
- All 24 enrolled athletes completed the intervention and post-testing.
- The article did not report adverse events during the intervention.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/40755811/) (pubmed)
- [DOI](https://doi.org/10.7717/peerj.19788) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12318499/) (full text)

## Agent Guidance

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