Muscle & Aging
Does Testosterone Therapy Build Muscle in Older Men?
The short answer
It depends on who was studied and what was measured. In frail, obese, hypogonadal men on a 6-month weight-loss program, testosterone preserved more lean mass and thigh muscle volume than placebo (-2% vs -4% loss, p=0.04) but did not add extra strength beyond diet and exercise alone (23% vs 22% gain, p=0.94). In mobility-limited older men with low-normal testosterone, testosterone gel did increase strength more than placebo — but the trial's safety monitors stopped enrollment early after adverse events rose in the testosterone group. In healthy, non-hypogonadal older men doing resistance training, testosterone injections increased both muscle mass and strength gains beyond training alone. A separate trial found lean mass increased only with an aromatase inhibitor, not with testosterone gel directly, complicating the simple story that more testosterone means more muscle.
Quick answers
- What is it?
- Whether testosterone therapy builds muscle in older men.
- Why are people interested in it?
- Older men considering testosterone therapy want to know if it actually adds muscle and strength.
- What has actually been studied?
- Four randomized trials in different populations: frail obese hypogonadal men on a weight-loss program (LITROS trial), mobility-limited men with low-normal testosterone (TOM trial), men given an aromatase inhibitor versus testosterone gel, and healthy older men doing resistance training.
- How strong is the evidence?
- It depends on who was studied and what was measured — testosterone preserved lean mass in some trials without adding strength, while in the TOM trial it increased strength but the trial was stopped early after adverse events rose.
- What don't we know yet?
- Whether the strength gains seen in mobility-limited men reduce falls or fractures, the full nature and long-term risk of the cardiovascular safety signal, and whether effects differ between clinically low testosterone and normal age-related decline.
- Where can I read the original research?
- Sources at the bottom of this page: Testosterone Replacement Therapy Added to Intensive Lifestyle Intervention in Older Men With Obesity and Hypogonadism and Clinical meaningfulness of the changes in muscle performance and physical function associated with testosterone administration in older men with mobility limitation.
The short answer: The randomized evidence doesn't give one answer — it gives four, depending on who was studied. In frail, obese, hypogonadal men going through a supervised weight-loss program, adding testosterone to diet and exercise preserved more lean mass and thigh muscle volume than placebo, but strength gains were the same in both groups. In mobility-limited older men with low-normal testosterone, a testosterone gel did increase strength beyond placebo — but the trial was stopped early by its own safety monitors after adverse events rose in the testosterone arm. In healthy, non-hypogonadal older men who did resistance training, testosterone injections boosted both muscle mass and strength gains beyond what training alone produced. And in a fourth trial, lean body mass rose only in men given an aromatase inhibitor — a drug that raises testosterone indirectly by blocking its conversion to estrogen — not in men given testosterone gel directly, suggesting the pathway to muscle gain may run partly through estrogen, not testosterone itself.
What the research shows
In frail, obese, hypogonadal men: muscle preserved, strength unchanged
The clearest modern trial here is a 2021 randomized, double-blind, placebo-controlled study (the LITROS trial) published in the Journal of Clinical Endocrinology & Metabolism. It enrolled 83 men aged 65 and older with obesity (BMI ≥30), persistently low morning testosterone (<10.4 nmol/L), and frailty, and randomized them to six months of lifestyle therapy (diet plus exercise) with either testosterone or placebo added. Both groups lost about 9% of body weight. The trial's primary outcome, an overall physical performance score, improved similarly in both groups (17% vs. 16%; p=0.58) — testosterone didn't add to overall function. But body composition told a different story: lean body mass and thigh muscle volume declined less with testosterone than placebo (-2% vs. -3%, p=0.01, and -2% vs. -4%, p=0.04), and hip bone mineral density was preserved with testosterone (0.5% vs. -1.1%, p=0.003) while it fell with placebo. Muscle strength, however, increased by nearly identical amounts in both groups (23% vs. 22%; p=0.94).
A follow-up mechanistic substudy of the same trial, published in 2025 with 38 of the original participants who underwent muscle biopsies, reproduced the same pattern — less lean mass and thigh volume loss with testosterone (-2% vs. -4%, p=0.04) and preserved bone density (0.4% vs. -1.3%, p=0.03), again with similar strength gains in both groups (23% vs. 24%; p=0.95). Gene-expression analysis found that testosterone limited the downregulation of muscle-atrophy-related pathways that occurred with weight loss under placebo, and increased expression of MYOD1 and WNT4, genes tied to muscle and bone building respectively. Aromatase inhibition wasn't tested in this trial.
In mobility-limited men: strength gains, but the trial didn't finish as planned
A separate, earlier trial — the Testosterone in Older Men with Mobility Limitations (TOM) trial, published in 2011 — took a different population: 209 men aged 65 and older with mobility limitation and low-to-low-normal testosterone, randomized to a daily testosterone gel or placebo for six months. Here, testosterone produced clear strength gains: significantly more men in the testosterone group exceeded a clinically meaningful improvement in leg-press and chest-press strength (43% vs. 18%, p=0.01) and in stair-climbing power (28% vs. 10%, p=0.03), compared with placebo. Walking speed, self-reported function, and fatigue did not differ between groups. But the trial's Data and Safety Monitoring Board recommended stopping enrollment before it reached its planned size, after adverse events occurred more frequently in the testosterone group than placebo — a signal serious enough that the study authors built their entire published analysis around weighing these strength gains against that risk.
A hormone-conversion twist
A third trial, published in Andrology in 2015, randomized 43 men aged 65-82 with low total testosterone to transdermal testosterone gel, an aromatase inhibitor (anastrozole, which blocks conversion of testosterone to estrogen and thereby raises circulating testosterone by a different mechanism), or placebo for 12 months. Both active treatments improved knee strength relative to baseline. But lean body mass increased significantly only in the aromatase-inhibitor group (+1.49 kg at 6 months, p<0.01; +1.24 kg at 12 months, p<0.05) — not in the group given testosterone gel directly. Testosterone gel, meanwhile, was the only treatment that improved bone density and fast gait speed. The authors concluded that aromatization — the conversion of testosterone into estradiol inside the body — appeared necessary for the lean-mass benefit, an unexpected wrinkle in a therapy usually framed as straightforwardly "more testosterone, more muscle."
In healthy older men doing resistance training: testosterone amplified the training response
A fourth trial looked at a different question entirely: does testosterone help healthy, non-hypogonadal older men get more out of resistance training? Eighteen men aged 65-75 were randomized to biweekly testosterone injections or placebo during six weeks of supervised whole-body resistance training. Testosterone increased total fat-free mass, leg and appendicular lean mass, and decreased fat mass more than training with placebo (p=0.02-0.007). Muscle thickness, fascicle length, and quadriceps cross-sectional area also increased more with testosterone (p<0.05), as did overall strength (p=0.0009) and maximal voluntary contraction (p=0.002). At the tissue level, muscle protein synthesis rates were higher with testosterone (2.13%/day vs. 1.34%/day, p=0.0009), as was protein breakdown — but net protein accretion, the balance of the two, was substantially higher with testosterone (8.3 g/day vs. 1.9 g/day, p=0.004).
What we don't know yet
Whether the strength gains seen in mobility-limited men reduce falls or fractures. The TOM trial measured strength and function, not downstream outcomes like falls, hospitalizations, or independence.
The full nature and long-term risk of the cardiovascular safety signal. The TOM trial's early stop for adverse events was a serious finding, but the trial wasn't designed or powered to characterize that risk precisely, and none of the other trials retrieved here ran long enough or enrolled enough participants to resolve it.
How long muscle-preserving effects last after testosterone is stopped. Every trial here ran for 6-12 months. None followed participants after discontinuation to see whether preserved muscle and bone reverted to the placebo trajectory.
Whether effects differ meaningfully between men with clinically low testosterone and men with normal-range, age-related decline. The trials enrolled somewhat different populations — hypogonadal and frail, mobility-limited with low-normal levels, or simply older and non-hypogonadal — and found different results, but no single trial directly compared these groups head-to-head.
Whether the aromatization finding replicates. One 43-person trial found lean mass gains required an aromatase inhibitor rather than testosterone itself — a striking result that, on this evidence alone, has not been confirmed in a larger or independent trial.
Sources
- Barnouin Y, Armamento-Villareal R, Celli A, et al. Testosterone Replacement Therapy Added to Intensive Lifestyle Intervention in Older Men With Obesity and Hypogonadism. The Journal of Clinical Endocrinology & Metabolism, 2021;106(3):e1096-e1110. DOI
- Travison TG, Basaria S, Storer TW, et al. Clinical meaningfulness of the changes in muscle performance and physical function associated with testosterone administration in older men with mobility limitation. The Journals of Gerontology: Series A, 2011;66(10):1090-1099. DOI
- Dias JP, Melvin D, Simonsick EM, et al. Effects of aromatase inhibition vs. testosterone in older men with low testosterone: randomized-controlled trial. Andrology, 2015;4(1):33-40. DOI
- Gharahdaghi N, Rudrappa S, Brook MS, et al. Testosterone therapy induces molecular programming augmenting physiological adaptations to resistance exercise in older men. Journal of Cachexia, Sarcopenia and Muscle, 2019;10(6):1276-1294. DOI
- Viola V, Samanta T, Nava MLD, et al. Testosterone Modulation of Muscle Transcriptomic Profile During Lifestyle Therapy in Older Men with Obesity and Hypogonadism. Journal of Cachexia, Sarcopenia and Muscle, 2025;16(1):e13697. DOI
Article records maintained via PubMed. Peptide Proof reports what studies found. It does not provide medical advice, dosing guidance, or treatment recommendations.
Topic: Energy & Performance · Aging & Longevity
Sources
- Testosterone Replacement Therapy Added to Intensive Lifestyle Intervention in Older Men With Obesity and Hypogonadism
- The Journal of Clinical Endocrinology & Metabolism, 2021 · n=83 · DOI
- Clinical meaningfulness of the changes in muscle performance and physical function associated with testosterone administration in older men with mobility limitation
- The Journals of Gerontology: Series A, 2011 · n=209 · DOI
- Effects of aromatase inhibition vs. testosterone in older men with low testosterone: randomized-controlled trial
- Andrology, 2015 · n=43 · DOI
- Testosterone therapy induces molecular programming augmenting physiological adaptations to resistance exercise in older men
- Journal of Cachexia, Sarcopenia and Muscle, 2019 · n=18 · DOI
- Testosterone Modulation of Muscle Transcriptomic Profile During Lifestyle Therapy in Older Men with Obesity and Hypogonadism
- Journal of Cachexia, Sarcopenia and Muscle, 2025 · n=38 · DOI
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