# 4 weeks of high-intensity interval training does not alter the exercise-induced growth hormone response in sedentary men

PMID: 25806146
Journal: SpringerPlus
Published: 2014-07-02
Authors: Sasaki H, Morishima T, Hasegawa Y, Mori A, Ijichi T, Kurihara T, Goto K

## Question

Does 4 weeks of submaximal cycling HIIT alter exercise-induced growth hormone responses and body or ectopic fat in sedentary men?

## Summary

In 24 healthy sedentary men, 4 weeks of cycling HIIT improved VO2max but did not change exercise-induced growth hormone response, whole-body fat, abdominal fat, intramyocellular lipid, or intrahepatic lipid. The authors noted the short, low-volume program and relatively lean healthy sample may have limited detectable endocrine or fat changes.

## Population

- Healthy sedentary men.
- Sample size: 24
- Sex: Male only
- Fitness level: Sedentary at baseline
- Health status: Healthy, mean BMI 23.9 +/- 0.5 kg/m2

## Methodology

- Randomized two-group training study
- 4 weeks
- University laboratory cycling and imaging assessments in Japan
- Randomized and controlled study design.

## Protocol

- Cycling HIT.
- Modality: Cycle ergometer.
- Work intervals: 1 minute.
- Recovery: 30 seconds rest.
- Sets or repetitions: 10 sets.
- Intensity: 85% VO2max.
- Session duration: About 14.5 minutes for HIT block.
- Frequency: 3 sessions/week.
- Program length: 4 weeks.
- Progression: Workload adjusted after 2-week VO2max reassessment.
- Low-intensity continuous training.
- Modality: Cycle ergometer.
- Work intervals: Continuous.
- Sets or repetitions: 22 minutes continuous.
- Intensity: 45% VO2max.
- Session duration: 22 minutes.
- Frequency: 3 sessions/week.
- Program length: 4 weeks.
- Progression: Workload adjusted after 2-week VO2max reassessment.

## Outcomes

### VO2max
Status: improved
VO2max increased significantly in both HIT and low-intensity groups, without a significant between-group difference.

HIT +8.3 +/- 2.6%; LT +4.7 +/- 1.3%; both p<.05 vs pre.

### GH response
Status: no clear change
Acute exercise increased GH, but training did not change the GH response in either group.

GH AUC did not significantly change pre to post in either group.

### Fat depots
Status: no clear change
Body weight, BMI, percent fat, abdominal fat area, IMCL, EMCL, and IHL did not significantly change.

No significant pre-post changes reported for these measures.

## Practical Insights

- Short low-volume cycling HIT can improve aerobic capacity without changing fat or GH outcomes.
- Growth-hormone claims are not supported by this 4-week protocol.
- Body-composition effects may require longer duration, higher volume, or different populations.

## Limitations

- Small sample.
- Male-only healthy sedentary participants.
- Short 4-week duration.
- Participants had relatively low fat accumulation and high baseline GH response.
- No high-intensity continuous comparator.

## Safety And Adherence

- No adverse events were reported in the reviewed text.
- HR was continuously monitored during training sessions.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/25806146/) (pubmed)
- [DOI](https://doi.org/10.1186/2193-1801-3-336) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4363223/) (full text)

## Agent Guidance

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