Age-Related Muscle Changes: Understanding the Impact and Solutions

June 14, 2023

Discover the effects of aging on muscle mass and strength, and explore whether these changes are primarily due to the natural aging process or a sedentary lifestyle.

As we age, one of the notable changes our bodies experience is the loss of muscle mass and strength. This decline can be attributed to various factors within the neuromuscular system, including a decrease in the number of motor neurons, muscle fibers, and muscle fiber size. However, it is crucial to determine whether these changes are solely a consequence of aging or a result of leading a sedentary lifestyle.

Age-Related Changes to Muscle

The decline in muscle mass associated with aging appears to occur in two phases. The first phase, known as the "slow" phase, involves a loss of 10% of muscle mass between the ages of 25 and 50. The majority of muscle loss occurs thereafter, with an additional 40% being lost from the ages of 50 to 85. By the age of 80, the human body loses approximately 50% of its muscle mass. This muscle atrophy can be attributed to significant decreases in both the total number of muscle fibers and the size of individual muscle fibers.

Research indicates that aging leads to a loss of fast-twitch fibers, particularly type IIb, which are responsible for generating power and speed. In contrast, there is an increase in slow-twitch fibers, which are more aerobic in nature. This shift aligns with the reduced demand for high-velocity contractions, such as jumping and sprinting, as we grow older.

Mechanisms of Strength Loss

The decline in strength contributes to various age-related health issues, including osteoporotic decline in bone density, arthritic joint pain, and a reduced overall functional capacity.

While a decrease in muscle mass is associated with a decrease in muscular strength, significant strength losses typically occur after the age of 60. The loss of motor units (nerve-muscle fiber complex), reduction in muscle fiber number, and decrease in muscle fiber size contribute to this strength decline. Interestingly, leg strength diminishes before upper extremity strength in the elderly, and strength, rather than cardiovascular function, is considered the most limiting factor in older individuals. This is evident in common activities faced by seniors, such as rising from a seated position or climbing stairs.

Encouragingly, aging does not seem to affect eccentric strength, which is important because poor eccentric strength has been linked to an increased risk of falls among the elderly.

The Importance of an Active Lifestyle

Regular exercise is the most effective way to slow down and counteract age-related muscle and strength loss. Comparisons between active and sedentary older adults highlight the significant influence of lifestyle factors on strength decline. Individuals who regularly engage certain muscles demonstrate less age-related strength decrease. In general, muscle atrophy and strength loss occur when muscles are not required to work against a given load, leading to decreased protein synthesis and increased protein breakdown. This muscle atrophy and weakness are similar to what is observed in astronauts during space flight. Incorporating regular resistance training is the most effective means of attenuating these effects.

Encouraging Findings

Numerous studies have consistently demonstrated that regular exercise can improve muscular endurance and strength in older adults, similar to the benefits observed in younger individuals. Notably, a large-scale study conducted at McMaster University showed that twice-weekly strength training (80-85% of one-repetition maximum) over a two-year period resulted in steady increases in strength across various muscle groups in individuals aged 60-80. The participants experienced significant gains in muscle mass along with improved function, as demonstrated by enhanced walking and stair climbing performance.

While certain changes are unavoidable with aging, it is possible to delay or mitigate the loss of muscle mass and strength typically associated with this process. Since strength is crucial for daily activities such as walking, climbing stairs, and standing up from a chair, it is imperative to minimize age-related strength decline. The muscles of older adults retain their ability to adapt, making regular resistance training (2-3 times per week) essential. Younger adults should also prioritize strength training as a preventive measure to maintain their health and well-being as they age.

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