Muscle and aging: what changes, and what training research shows

Key numbers

20 to 30%

strength loss over 12 years in 9 healthy, sedentary older men

14.7%

loss of thigh muscle cross-sectional area in 7 of those men

0.64-0.70%

yearly muscle mass loss in women aged 75 (longitudinal studies)

What changes with age

Aging changes muscle in two ways: how much of it there is, and how well it works. Understanding the effect of age means paying attention to both.

One long-term study followed healthy, sedentary older men for 12 years. Nine were reassessed, and seven of them had CT scans. Strength of the knee and elbow muscles fell by 20 to 30%. The cross-sectional area of all the thigh muscles fell by 14.7%, and of the thigh flexor muscles by 14.9%. Those are measures of muscle area, not of how many muscle fibers a person has.

In those men, starting strength together with the loss of thigh muscle area accounted for 90% of the variation in strength 12 years later. The authors suggest the loss of muscle area is a major contributor to falling strength. It is a small, all-male, observational study, so that is an association, not proof of cause.

Part of the change is in the nervous system. A review of how nerve cells drive muscle supports slower motor-unit firing rates as one contributor to the decline in fast force production with age.

How fast, and why strength matters

There is no single yearly rate of muscle loss that applies to everyone. Studies comparing younger adults (18-45 years) with older adults (over 65 years) at one point in time give very different estimates depending on the measurement method and the people studied.

Studies that follow the same people over time put muscle loss at age 75 at 0.64-0.70% a year in women.

In a separate cohort of older adults, leg lean mass fell by approximately 1% a year while leg strength fell faster. That gap suggests muscle quality declines with age, and keeping muscle mass did not guarantee keeping strength.

A review of this research concluded that loss of strength is a more consistent risk factor for disability and death than loss of muscle mass. That does not make muscle mass unimportant.

What training research shows

A systematic review and meta-analysis of healthy older adults found resistance training improved strength in the upper and lower body and improved muscle size and structure.

The review also found dose-response relationships linked to larger gains, but the trials used very different programs and varied in quality, so they do not prove one best dose for everyone. Only nine studies measured muscle size and structure, and the authors treated those results as preliminary.

In this capacity

The evidence

Each cited source is labeled according to how it supports the particular claim on this page. Direct test evidence, underlying-capacity findings and population reference values are distinguished from Systematic-defined protocols and standards. Historical development notes are retained internally rather than presented as public evidence. A study of an underlying capacity is never presented as validation of the Systematic test itself.

Underlying-capacity evidence New source

Borde et al. (2015). Dose-Response Relationships of Resistance Training in Healthy Old Adults: A Systematic Review and Meta-Analysis. Sports medicine (Auckland, N.Z.).

What it found. Resistance training improved upper and lower body strength and muscle size and structure in healthy older adults, with dose-response relationships linked to larger gains.

What it does not show. It does not prove one best dose for everyone; protocols and study quality varied, and the muscle-size findings rest on only nine studies.

PubMed 26420238
Underlying-capacity evidence New source

Frontera et al. (2000). Aging of skeletal muscle: a 12-yr longitudinal study. Journal of applied physiology (Bethesda, Md. : 1985).

What it found. Over 12 years, 9 healthy sedentary older men lost 20 to 30% of knee and elbow strength; in the 7 with CT scans, thigh muscle cross-sectional area fell by 14.7%.

What it does not show. It does not show that the loss of muscle area caused the loss of strength, does not measure fiber count, and studied only a small group of men.

PubMed 10749826
Normative/reference evidence New source

Mitchell et al. (2012). Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Frontiers in physiology.

What it found. Estimates of muscle loss vary widely by method and population; longitudinal studies put loss at age 75 at 0.64-0.70% a year in women, and strength loss is a more consistent risk factor for disability and death than mass loss.

What it does not show. It does not give one yearly rate of muscle loss for everyone, and it does not show muscle mass is irrelevant.

PubMed 22934016
Underlying-capacity evidence New source

Goodpaster et al. (2006). The loss of skeletal muscle strength, mass, and quality in older adults: the health, aging and body composition study. The journals of gerontology. Series A, Biological sciences and medical sciences.

What it found. In this older-adult cohort (Health ABC), leg strength fell faster than leg lean mass, which fell by approximately 1% a year.

What it does not show. It does not mean muscle quantity is unimportant, and the cohort rate is not a rate every individual will follow.

PubMed 17077199
Underlying-capacity evidence

Orssatto et al. (2022). Do motoneuron discharge rates slow with aging? A systematic review and meta-analysis. Mechanisms of Ageing and Development.

What it found. Slower motor-unit firing rates are supported as one contributor to the age-related decline in fast force production.

What it does not show. It is one contributor among several, and it says nothing about any Systematic test.

DOI 10.1016/j.mad.2022.111647

The Systematic Healthspan Assessment is a physical baseline. It is not a diagnosis, and it does not estimate a biological age, a disease risk or a lifespan.