A progressive loss of muscle mass and function generally begins around the fourth to fifth decade of life, and the rate of decline increases with advancing age.^[19] The rate of the age-related decline in muscle strength (about 1%–3% per year) and power (about 3%–4% per year) exceeds that of muscle loss (about 0.5%–1.5% per year).^[19] What mechanisms explain this comparatively accelerated loss of muscle strength and power (i.e., muscle function)?

Total muscle mass and muscle strength are strongly correlated,^[20][21] so one might expect that the rate of decline for muscle mass and muscle strength would be more similar than they are. The primary reason for this discrepancy seems to be the type of muscle atrophy occurring.

Muscle fibers come in different types based on their speed of contraction and metabolism, and they are generally categorized as slow-twitch (type I) and fast-twitch (type II). Type I muscle fibers contract relatively slowly and are more resistant to fatigue, whereas type II muscle fibers contract with more velocity and produce significantly more power but are quick to fatigue.

Older adults predominantly experience a reduction in the size of type II muscle fibers, while type I muscle fiber size (and perhaps even their potential for hypertrophy) is preserved.^[19] Furthermore, there’s evidence to suggest that type II muscle fibers in older adults are less sensitive to calcium,^[22][23][24] which is detrimental for force production, as calcium triggers muscle contraction.

Other factors thought to contribute to the decline in muscle function with aging are a progressive increase in myosteatosis (i.e., fat infiltration within skeletal muscle),^[25] satellite cell loss and dysfunction,^[26][27] and mitochondrial dysfunction.^[28]

Resistance exercise using relatively heavy loads (≥70% of 1-repetition maximum) is undeniably effective for increasing muscle mass and strength and improving physical performance.^[29][7][8] However, some individuals are apprehensive about lifting heavy loads due to the risk of injury — particularly when performed without oversight from a personal trainer — while others don’t have access to a gym. Fortunately, emerging evidence suggests that lifting relatively light loads (approximately 35%–50% of 1-repetition maximum) exerts similar benefits,^[30][9] particularly when each set is performed to volitional fatigue.

This suggests that meaningful improvements in muscle mass, strength, and physical performance can be achieved by performing resistance exercise using one’s own body weight or with minimal equipment (e.g., ankle weights, elastic bands), as long as the individual is exerting a high degree of effort during their workouts.

It’s recommended that from midlife on, adults interested in healthy muscle aging perform resistance exercise at least twice per week.^[30] The program should be progressive in nature (i.e., there is an increase in the number of repetitions performed or the amount of load lifted over time) and each workout should comprise a full-body approach with multiple sets (about 2–4) performed per exercise.^[7]

Supplementing with creatine enhances resistance-exercise-induced gains in lean mass and upper- and lower-body strength.^[31] Some evidence suggests that supplementing with whey protein and/or vitamin D can enhance certain measures of muscle strength and physical performance.^[32][33][34] Also, supplementing with omega-3 fatty acids may enhance improvements in performance on the TUG test.^[35]

In longitudinal trials, supplementing with leucine has not been found to enhance resistance-exercise-induced gains in muscle mass, muscle strength, or physical performance.^[36][37] However, supplementing a suboptimal dose of protein (10–20 grams) with leucine has been shown to enhance rates of muscle protein synthesis,^{[38][39][40][41]} so leucine may augment the benefits of resistance exercise in the context of a diet with suboptimal protein content, but further research is needed.