# HIIT produces increases in muscle power and free testosterone in male masters athletes

PMID: 28794164
Journal: Endocrine Connections
Published: 2017
Authors: Herbert P, Hayes LD, Sculthorpe NF, Grace FM

## Question

Does replacing normal training with six weeks of low-volume, low-frequency HIIT improve peak power output and alter steroid hormones in male masters athletes?

## Summary

Seventeen male masters athletes replaced their usual high-volume aerobic training with supervised low-frequency cycling HIIT for six weeks. Peak power output increased, free testosterone rose slightly, total testosterone did not significantly change, and cortisol increased with a lower testosterone:cortisol ratio, suggesting benefit but also meaningful training stress.

## Population

- 17 male masters athletes from endurance and team sports.
- Sample size: 17
- Age: 60 +/- 5 years
- Sex: Male only
- Fitness level: Highly active masters athletes with >30 years exercise history
- Health status: General practitioner approval to exercise

## Methodology

- Single-arm prospective cohort with a habitual-training observation phase followed by HIIT
- Habitual training for 6 weeks followed by 6 weeks of HIIT
- Supervised laboratory/group cycling HIIT sessions

## Protocol

- Low-frequency masters cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 30 s.
- Recovery: 3 min active recovery.
- Sets or repetitions: 6.
- Intensity: 40% PPO; mean 126 +/- 22% of power at VO2peak.
- Session duration: About 18 min interval/recovery time; warm-up not reported.
- Frequency: Once every 5 days.
- Program length: 6 weeks.
- Progression: None reported.
- Habitual training observation.
- Modality: Participant normal sports training.
- Intensity: 214 +/- 131 min/week <65% HRR and 67 +/- 52 min/week >=65% HRR.
- Session duration: 281 min/week average total habitual training.
- Frequency: Habitual.
- Program length: 6 weeks.
- Progression: Maintain habitual practices.

## Outcomes

### PPO
Status: improved
Absolute and relative peak power output increased after HIIT.

Absolute PPO 799 +/- 205 to 865 +/- 211 W, p<0.001, d=0.32; relative PPO 10.2 +/- 2.0 to 11.0 +/- 2.2 W/kg, p<0.001, d=0.38.

### Free testosterone
Status: improved
Calculated free testosterone increased slightly after HIIT.

7.0 +/- 1.2 to 7.5 +/- 1.1 ng/dL, p=0.050, d=0.40.

### Total testosterone
Status: no clear change
Total testosterone did not significantly change after HIIT.

15.2 +/- 4.2 to 16.4 +/- 3.3 nmol/L, p=0.061.

### Stress hormones
Status: worse/safety concern
Cortisol increased and testosterone:cortisol ratio decreased after HIIT.

Cortisol p=0.01, d=0.90; T:C p=0.017, d=0.69.

## Practical Insights

- For older trained athletes, HIIT every five days can be enough to improve cycling peak power while sharply reducing training volume.
- Recovery spacing matters: the authors selected five-day spacing based on prior recovery data in older males.

## Limitations

- Single-arm design
- No randomized control or moderate-intensity comparison
- Male masters athletes only
- Calculated free testosterone
- Lab power outcome rather than competition outcome

## Safety And Adherence

- No adverse events or injuries were reported.
- Participants had general practitioner approval to exercise and HIIT was spaced every five days.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/28794164/) (pubmed)
- [DOI](https://doi.org/10.1530/EC-17-0159) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5551442/) (full text)

## Agent Guidance

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