Why am I losing muscle after 40, and what stops it?
Written and medically reviewed by Zahraa Sater, M.D., M.P.H.
Reviewed August 12, 2026 · Next review due August 12, 2028
Short answer
Muscle loss after 40 comes from ageing plus the menopause transition. The American Heart Association scientific statement reports that lean mass declines and fat gain accelerates from about two years before the final period until two years after. Resistance training and adequate protein are the only interventions with consistent evidence for holding on to muscle.
Losing muscle after 40 is partly ageing and partly menopause, and the two overlap. The American Heart Association scientific statement on the menopause transition reports that lean mass declined while the rate of fat gain doubled, beginning about two years before the final menstrual period and continuing until roughly two years after it. The statement describes these as menopause related rather than purely age related changes, which is why the drop often feels sudden rather than gradual.
Why muscle matters beyond appearance
Muscle is the largest site of glucose disposal in the body, so losing it makes blood sugar harder to control. It is also the main defence against falls, and falls are what turn thinning bone into a fractured hip. Strength predicts independence in later decades better than weight does. This is the reason body composition, rather than the number on the scale, is the useful measure through the transition.
What actually preserves muscle
Two interventions carry the evidence. The Physical Activity Guidelines for Americans, second edition, recommend muscle strengthening activities involving all major muscle groups on two or more days a week, alongside weekly aerobic activity. Adequate protein is the second, and the 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society names adequate protein intake with strength training as a priority for preserving lean mass during weight reduction. Neither is optional if muscle is the target.
What does not preserve muscle
| Approach | Effect on muscle |
|---|---|
| Resistance training two or more days weekly | The primary stimulus for retaining lean mass |
| Protein distributed across meals | Supports the training stimulus |
| Walking or cardio alone | Good for the heart, insufficient stimulus for muscle |
| Aggressive calorie restriction without training | A substantial share of the weight lost is lean mass |
| Testosterone therapy | Not supported for muscle in women by the 2019 global consensus |
Measure something you can repeat at home: how many times you can stand from a chair in 30 seconds, or whether you can carry the shopping up a flight of stairs without stopping. Recheck it every eight to twelve weeks. If you are also losing weight, whether through diet or medication, resistance training moves from useful to necessary, because weight loss without a training stimulus takes muscle with the fat.
The clinical detail
The 2020 American Heart Association scientific statement places the inflection in body composition at roughly two years before the final menstrual period, with accelerated fat gain and lean mass decline continuing to about two years afterwards. Function can be tracked in clinic without imaging: 30 second sit to stand repetitions, gait speed over 4 metres, and hand grip dynamometry. DXA quantifies appendicular lean mass where the change is clinically ambiguous. The Physical Activity Guidelines for Americans, second edition, set muscle strengthening on 2 or more days weekly across all major muscle groups as the adult standard, which is a floor rather than a target for women in the menopause transition.
Written and medically reviewed by Zahraa Sater, M.D., M.P.H.
Reviewed August 12, 2026 · Next review due August 12, 2028
Sources
- Menopause Transition and Cardiovascular Disease Risk: Implications for Timing of Early Prevention. Circulation, American Heart Association. doi:10.1161/CIR.0000000000000912
- Physical Activity Guidelines for Americans, second edition. Office of Disease Prevention and Health Promotion, U.S. Department of Health and Human Services
- Nutritional Priorities to Support GLP-1 Therapy for Obesity, joint advisory. American Society for Nutrition
- Global Consensus Position Statement on the Use of Testosterone Therapy for Women. Journal of Clinical Endocrinology and Metabolism. PMID 31498871
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