# The Effect of High-Intensity Interval Training Periods on Morning Serum Testosterone and Cortisol Levels and Physical Fitness in Men Aged 35-40 Years

PMID: 34063524
Journal: Journal of clinical medicine
Published: 2021 May 15
Authors: Ambroży T, Rydzik Ł, Obmiński Z, Błach W, Serafin N, Błach B, Jaszczur-Nowicki J, Ozimek M

## Question

How does an eight-week high-intensity interval endurance-and-strength program affect morning testosterone, cortisol, T/C ratio, VO2max, and physical fitness in men aged 35-40?

## Summary

In healthy recreationally trained men aged 35-40, an eight-week supervised high-intensity endurance-and-strength circuit program increased morning testosterone and testosterone-to-cortisol ratio and improved several strength/endurance fitness tests. VO2max did not significantly improve.

## Population

- Healthy men aged 35-40 with at least 2 years of recreational training experience.
- Sample size: 30
- Age: 35-40 years
- Sex: Male
- Fitness level: Recreationally trained
- Health status: Healthy; no regular medication; no endocrine disorders or fertility problems

## Methodology

- Randomized controlled intervention
- 8 weeks
- Supervised training program with laboratory blood and fitness testing
- Randomized and controlled study design.

## Protocol

- High-intensity endurance and strength circuit training.
- Modality: Mixed bodyweight, dumbbell, and kettlebell circuit exercises.
- Work intervals: 60 seconds high-intensity activity in 2:1 interval portion.
- Recovery: 30 seconds rest in 2:1 interval portion.
- Sets or repetitions: 10 exercises in interval circuit plus kettlebell strength circuits.
- Intensity: High-intensity circuit training; exact HR/RPE target not reported.
- Session duration: 60 minutes.
- Frequency: 3 sessions per week.
- Program length: 8 weeks.
- Progression: Kettlebell loads and circuit counts progressed gradually.
- Usual recreational activity control.
- Modality: Participants continued previous recreational activity.
- Intensity: Not programmed by investigators.
- Program length: 8 weeks.

## Outcomes

### Testosterone
Status: improved
Morning testosterone increased significantly in the experimental group.

Experimental group +36.7%; control +6% not significant.

### Cortisol
Status: no clear change
Mean cortisol did not significantly change within groups.

Experimental group had about a 12% decrease, but within-group change was not significant.

### T/C ratio
Status: improved
The testosterone-to-cortisol ratio increased significantly in the experimental group.

Experimental group +59%; control +16% not significant.

### VO2max
Status: no clear change
VO2max did not significantly improve despite a small numerical increase in the experimental group.

Experimental group about +11.8%, not statistically significant.

### Fitness tests
Status: improved
Several muscular endurance and power tests improved in the experimental group.

Significant improvements were reported for abdominal/upper-body endurance, pull-up, and standing long jump tests.

## Practical Insights

- A supervised 60-minute mixed interval and strength-circuit program may improve hormonal and muscular fitness markers in recreationally trained midlife men.
- This was not a pure cardiorespiratory HIIT protocol; it resembled combined resistance and interval circuit training.
- VO2max did not significantly improve, so aerobic-fitness claims should be cautious.

## Limitations

- Small sample of men aged 35-40.
- Only testosterone and cortisol were evaluated among hormonal/biochemical mechanisms.
- No follow-up to determine persistence after return to prior activity.
- The intervention combined endurance, interval, and strength training, making the active ingredient unclear.
- Exercise intensity was not reported with precise HR or RPE targets.

## Safety And Adherence

- Participants provided a medical certificate indicating no contraindication to high-intensity training.
- No adverse events or dropouts were reported in the extracted text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/34063524/) (pubmed)
- [DOI](https://doi.org/10.3390/jcm10102143) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8156527/) (full text)

## Agent Guidance

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