Study analysis · Endocrine Connections · 2017
A 12-week exercise program raised total testosterone by 17% in formerly sedentary older men—but the active form barely budged. Here is why that matters.
In 22 older men who had not exercised in decades, 12 weeks of moderate exercise plus HIIT was linked to higher total testosterone, but only a tiny rise in the active form.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study followed a small group of older men who started exercising. It found their testosterone went up, but because there was no comparison group, we can't be sure the exercise caused the change. It could be other things like time or natural variation.
What’s the bottom line?
Twenty-two men around age 62 who had not exercised for decades did 6 weeks of moderate aerobic exercise, then 6 weeks of high-intensity interval training (HIIT). Blood tests showed total testosterone went up, especially in the first 6 weeks. Free testosterone—the active form—went up a little only after HIIT. They also lost some body fat and gained a little muscle.
How strong is this study?
The study is not very strong because it only looked at 22 men and had no control group. That means we can't trust the results as much as we would from a study where some people exercised and others didn't.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
15 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=22)+2.1/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. Single-arm pre-post design with no control group, no randomization, and small sample size. Cannot rule out confounding, regression to the mean, placebo effects, or natural variation. Changes over time cannot be attributed to HIIT or conditioning exercise.
No Conflicts
No conflicts of interest identified
No conflicts identified; authors declare no conflict of interest and no specific funding from any agency.
No author affiliations or names were provided in the analyzed text. The study mentions equipment from Wattbike Ltd. and Tanita UK Ltd., but no financial relationships or conflicts are disclosed. The single-arm observational design is a limitation noted by authors, but not a COI.
Key takeaways
- 01
Total testosterone rose from 13.2 to 15.4 nmol/L: about a 17% relative increase, or +2.2 nmol/L absolute.
- 02
Most of that rise happened during the first 6 weeks of moderate exercise: about 10% relative increase.
- 03
Free testosterone did not change after moderate exercise, but rose from 6.6 to 7.3 ng/dL after HIIT: about a 4.5% relative increase, or +0.7 ng/dL absolute.
- 04
SHBG increased, cortisol stayed the same.
- 05
Body fat percentage dropped by about 3.3 percentage points; fat-free mass increased by about 3.6% relative.
- 06
This was a small single-arm study, so there was no untreated comparison group.
- 07
No absolute risk is reported because the outcomes are hormone levels, not disease events.
- 08
The free testosterone rise was only +0.7 ng/dL, and the authors say its biological or clinical importance is uncertain.
- 09
The total testosterone rise was +2.2 nmol/L, but it is unclear how much was due to HIIT itself versus exercise in general or body-fat loss.
Surprising findings
- Most of the total testosterone increase occurred during moderate aerobic preconditioning, not HIIT.HIIT is often marketed as the superior method for hormonal benefits, but here the first 6 weeks of moderate exercise produced ~10% relative increase, with only a small additional rise after HIIT.
- Free testosterone did not increase after moderate exercise, only after HIIT, but the rise was tiny and of uncertain significance.If total T rose 17%, you would expect free T to follow, but SHBG rose and free T only rose ~4.5% relative after HIIT.
- Cortisol did not change despite six weeks of high-intensity interval training.Intense exercise is often thought to chronically elevate cortisol, but this study found no significant change.
Practical takeaways
For sedentary older men, starting with moderate aerobic exercise (150 min/week) may raise total testosterone; adding HIIT may give a small free-T bump.
Single-arm study, n=22, no control group; effects small and clinical significance unknown.
low confidenceDo not use exercise as a replacement for medically indicated testosterone therapy without consulting a doctor.
Low testosterone is linked to real health risks; this study does not test clinical outcomes.
low confidenceFocus on overall body composition—fat loss and muscle gain may mediate hormone improvements.
Body composition changes may be the real driver, not exercise modality.
medium confidenceIf you are new to exercise, precondition before HIIT; the study used 6 weeks of moderate exercise first.
Protocol was supervised and specific to older sedentary men.
medium confidenceWhy this study matters
Total T jumped 17%—but most of it came from moderate exercise
Total testosterone rose from 13.2±5.5 to 15.4±6.6 nmol/L, a ~17% relative increase (absolute +2.2 nmol/L, P<0.001, d=0.36). But ~10% relative increase happened during the first 6 weeks of moderate aerobic preconditioning (P=0.007, d=0.24), before any HIIT.
People assume HIIT is the hormonal magic bullet, but here moderate exercise did the heavy lifting.
Free testosterone only rose after HIIT—and only a little
Free-T was unchanged after moderate exercise (6.6±1.9 to 7.0±1.8 ng/dL, P=0.102), then rose to 7.3±2.1 ng/dL after HIIT: ~4.5% relative increase (absolute +0.7 ng/dL, P=0.023, d=0.36). Authors say clinical importance is uncertain.
Free T is the active form; a tiny bump may not translate to real benefits.
SHBG rose, possibly canceling out the total T boost
SHBG increased from 42.6±22.0 to 45.0±23.9 nmol/L after preconditioning (P=0.016) and to 45.9±24.6 after HIIT (P=0.003). More SHBG binds testosterone, limiting free-T.
More total testosterone does not mean more usable testosterone.
No cortisol spike from intense intervals
Cortisol remained unchanged from baseline (302±114 nmol/L) to post-HIIT (256±86 nmol/L, P=0.138, d=0.46).
Many believe HIIT chronically raises stress hormones; this small study found no change.
Body composition changed, which may explain hormone shifts
Body fat dropped ~3.3 percentage points and fat-free mass rose ~3.6% relative from baseline to post-HIIT. The authors note lower body fat may have driven free-T increases rather than HIIT alone.
It is a reminder that hormones do not change in a vacuum—body composition matters.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Twenty-two men around age 62 who had not exercised for decades did 6 weeks of moderate aerobic exercise, then 6 weeks of high-intensity interval training (HIIT). Blood tests showed total testosterone went up, especially in the first 6 weeks. Free testosterone—the active form—went up a little only after HIIT. They also lost some body fat and gained a little muscle.
Research results
Total testosterone rose from 13.2 to 15.4 nmol/L: about a 17% relative increase, or +2.2 nmol/L absolute. Most of that rise happened during the first 6 weeks of moderate exercise: about 10% relative increase. Free testosterone did not change after moderate exercise, but rose from 6.6 to 7.3 ng/dL after HIIT: about a 4.5% relative increase, or +0.7 ng/dL absolute. SHBG increased, cortisol stayed the same. Body fat percentage dropped by about 3.3 percentage points; fat-free mass increased by about 3.6% relative.
What this means - more context
This was a small single-arm study, so there was no untreated comparison group. No absolute risk is reported because the outcomes are hormone levels, not disease events. The free testosterone rise was only +0.7 ng/dL, and the authors say its biological or clinical importance is uncertain. The total testosterone rise was +2.2 nmol/L, but it is unclear how much was due to HIIT itself versus exercise in general or body-fat loss.
To examine whether high-intensity interval training (HIIT) following moderate aerobic preconditioning alters total testosterone (TT), sex hormone-binding globulin (SHBG), free testosterone (free-T), and cortisol in lifelong sedentary older men.
In 22 lifelong sedentary men (62±2 years), a 12-week program of 6 weeks moderate aerobic preconditioning followed by 6 weeks HIIT was associated with a ~17% relative increase in total testosterone from 13.2±5.5 to 15.4±6.6 nmol/L (absolute +2.2 nmol/L; P<0.001; d=0.36), with most increase (~10% relative) during preconditioning. Free testosterone was unchanged after preconditioning but rose ~4.5% relative after HIIT (6.6±1.9 to 7.3±2.1 ng/dL; absolute +0.7 ng/dL; P=0.023; d=0.36). SHBG increased; cortisol was unchanged. Body fat decreased ~3.3 percentage points and fat-free mass increased ~3.6% relative. Authors caution the small free-T rise may not be biologically or clinically significant.
Methods Used
Prospective single-arm cohort; 22 sedentary but healthy men (62±2 y; body mass 91±16 kg). Six weeks moderate aerobic preconditioning (150 min/week) then six weeks supervised HIIT (9 sessions; 6×30-s sprints at 40% peak power output, 3-min active recovery). Serum TT, SHBG, cortisol by electrochemiluminescent immunoassay; free-T calculated by Vermeulen equation; body composition by bioelectrical impedance. Repeated-measures ANOVA with Bonferroni correction; Cohen’s d reported.
Main Finding
Combined moderate aerobic preconditioning plus HIIT increased total testosterone by ~17% relative (from 13.2±5.5 to 15.4±6.6 nmol/L; absolute +2.2 nmol/L; P<0.001; d=0.36), with most of the rise (~10% relative; P=0.007) occurring during the first 6 weeks of moderate exercise. Free testosterone increased only after HIIT by ~4.5% relative (from 6.6±1.9 to 7.3±2.1 ng/dL; absolute +0.7 ng/dL; P=0.023; d=0.36). SHBG increased significantly; cortisol did not change. Absolute risk not applicable (hormone outcomes, not disease events); authors state biological importance of small free-T improvement is uncertain.
Confidence Level
Low to moderate. Small single-arm cohort (n=22), no control group or randomization, short 12-week follow-up, no confidence intervals; effect sizes small; free-T was calculated rather than directly measured; body-composition changes may mediate hormone changes; authors note clinical significance uncertain. Not retracted and no corrections noted.
Study Flags
Red Flags
- •Single-arm observational design with no control group; cannot isolate HIIT effect from general exercise or time
- •Small sample (n=22), short 12-week follow-up, and no confidence intervals reported
- •Small free-T increase (~4.5% relative, +0.7 ng/dL) of uncertain biological/clinical significance; body-composition changes may mediate hormone effects
Surprising Findings
Most of the total testosterone increase occurred during moderate aerobic preconditioning, not HIIT.
HIIT is often marketed as the superior method for hormonal benefits, but here the first 6 weeks of moderate exercise produced ~10% relative increase, with only a small additional rise after HIIT.
Practical Takeaways
For sedentary older men, starting with moderate aerobic exercise (150 min/week) may raise total testosterone; adding HIIT may give a small free-T bump.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study followed a small group of older men who started exercising. It found their testosterone went up, but because there was no comparison group, we can't be sure the exercise caused the change. It could be other things like time or natural variation.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Repeated-measures design with three time points within the same participants.
- Supervised and standardized exercise intervention.
- Identical measurement methods at each phase.
Weaknesses
- No control group or randomization.
- Single-arm observational design; cannot isolate effect of HIIT from preconditioning or other factors.
- Small sample size (n=22).
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Twenty-two men around age 62 who had not exercised for decades did 6 weeks of moderate aerobic exercise, then 6 weeks of high-intensity interval training (HIIT). Blood tests showed total testosterone went up, especially in the first 6 weeks. Free testosterone—the active form—went up a little only after HIIT. They also lost some body fat and gained a little muscle.
Research results
Total testosterone rose from 13.2 to 15.4 nmol/L: about a 17% relative increase, or +2.2 nmol/L absolute. Most of that rise happened during the first 6 weeks of moderate exercise: about 10% relative increase. Free testosterone did not change after moderate exercise, but rose from 6.6 to 7.3 ng/dL after HIIT: about a 4.5% relative increase, or +0.7 ng/dL absolute. SHBG increased, cortisol stayed the same. Body fat percentage dropped by about 3.3 percentage points; fat-free mass increased by about 3.6% relative.
What this means - more context
This was a small single-arm study, so there was no untreated comparison group. No absolute risk is reported because the outcomes are hormone levels, not disease events. The free testosterone rise was only +0.7 ng/dL, and the authors say its biological or clinical importance is uncertain. The total testosterone rise was +2.2 nmol/L, but it is unclear how much was due to HIIT itself versus exercise in general or body-fat loss.
To examine whether high-intensity interval training (HIIT) following moderate aerobic preconditioning alters total testosterone (TT), sex hormone-binding globulin (SHBG), free testosterone (free-T), and cortisol in lifelong sedentary older men.
In 22 lifelong sedentary men (62±2 years), a 12-week program of 6 weeks moderate aerobic preconditioning followed by 6 weeks HIIT was associated with a ~17% relative increase in total testosterone from 13.2±5.5 to 15.4±6.6 nmol/L (absolute +2.2 nmol/L; P<0.001; d=0.36), with most increase (~10% relative) during preconditioning. Free testosterone was unchanged after preconditioning but rose ~4.5% relative after HIIT (6.6±1.9 to 7.3±2.1 ng/dL; absolute +0.7 ng/dL; P=0.023; d=0.36). SHBG increased; cortisol was unchanged. Body fat decreased ~3.3 percentage points and fat-free mass increased ~3.6% relative. Authors caution the small free-T rise may not be biologically or clinically significant.
Methods Used
Prospective single-arm cohort; 22 sedentary but healthy men (62±2 y; body mass 91±16 kg). Six weeks moderate aerobic preconditioning (150 min/week) then six weeks supervised HIIT (9 sessions; 6×30-s sprints at 40% peak power output, 3-min active recovery). Serum TT, SHBG, cortisol by electrochemiluminescent immunoassay; free-T calculated by Vermeulen equation; body composition by bioelectrical impedance. Repeated-measures ANOVA with Bonferroni correction; Cohen’s d reported.
Main Finding
Combined moderate aerobic preconditioning plus HIIT increased total testosterone by ~17% relative (from 13.2±5.5 to 15.4±6.6 nmol/L; absolute +2.2 nmol/L; P<0.001; d=0.36), with most of the rise (~10% relative; P=0.007) occurring during the first 6 weeks of moderate exercise. Free testosterone increased only after HIIT by ~4.5% relative (from 6.6±1.9 to 7.3±2.1 ng/dL; absolute +0.7 ng/dL; P=0.023; d=0.36). SHBG increased significantly; cortisol did not change. Absolute risk not applicable (hormone outcomes, not disease events); authors state biological importance of small free-T improvement is uncertain.
Confidence Level
Low to moderate. Small single-arm cohort (n=22), no control group or randomization, short 12-week follow-up, no confidence intervals; effect sizes small; free-T was calculated rather than directly measured; body-composition changes may mediate hormone changes; authors note clinical significance uncertain. Not retracted and no corrections noted.
Study Flags
Red Flags
- •Single-arm observational design with no control group; cannot isolate HIIT effect from general exercise or time
- •Small sample (n=22), short 12-week follow-up, and no confidence intervals reported
- •Small free-T increase (~4.5% relative, +0.7 ng/dL) of uncertain biological/clinical significance; body-composition changes may mediate hormone effects
Surprising Findings
Most of the total testosterone increase occurred during moderate aerobic preconditioning, not HIIT.
HIIT is often marketed as the superior method for hormonal benefits, but here the first 6 weeks of moderate exercise produced ~10% relative increase, with only a small additional rise after HIIT.
Practical Takeaways
For sedentary older men, starting with moderate aerobic exercise (150 min/week) may raise total testosterone; adding HIIT may give a small free-T bump.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study followed a small group of older men who started exercising. It found their testosterone went up, but because there was no comparison group, we can't be sure the exercise caused the change. It could be other things like time or natural variation.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Repeated-measures design with three time points within the same participants.
- Supervised and standardized exercise intervention.
- Identical measurement methods at each phase.
Weaknesses
- No control group or randomization.
- Single-arm observational design; cannot isolate effect of HIIT from preconditioning or other factors.
- Small sample size (n=22).
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study is not very strong because it only looked at 22 men and had no control group. That means we can't trust the results as much as we would from a study where some people exercised and others didn't.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
15 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=22)+2.1/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. Single-arm pre-post design with no control group, no randomization, and small sample size. Cannot rule out confounding, regression to the mean, placebo effects, or natural variation. Changes over time cannot be attributed to HIIT or conditioning exercise.
No Conflicts
No conflicts of interest identified
No conflicts identified; authors declare no conflict of interest and no specific funding from any agency.
No author affiliations or names were provided in the analyzed text. The study mentions equipment from Wattbike Ltd. and Tanita UK Ltd., but no financial relationships or conflicts are disclosed. The single-arm observational design is a limitation noted by authors, but not a COI.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
4 researchersIf this is your work, this is how we attribute it on Fit Body Science. Lawrence D. Hayes is listed as the lead author.