Athena Vale
Muscle ageing is a natural part of the human ageing process. It is believed that muscle loss begins at around 25 and progresses at an accelerated rate from that point. The speed and amount of muscle loss seem to be caused by genetics. The loss of muscle tissue (atrophy) is caused by a reduction in muscle cell number, muscle twitch time, and twitch force, among other factors. This loss of muscle tissue can lead to weakness and slowed movement, affecting an individual's balance and gait. While muscle ageing is a natural process, it can be slowed down with exercise and a well-balanced diet.
| Characteristics | Values |
|---|---|
| Age-related muscle loss | Begins at around 30 years of age, with a loss of 3% to 5% per decade |
| Muscle fiber loss | Due to a loss in motor neurons |
| Sarcopenia | Loss of muscle mass and strength |
| Hormonal changes | Decrease in testosterone levels in men |
| Insulin resistance | Prevalence increases with aging |
| Joint problems | Mild stiffness to debilitating arthritis |
| Gait changes | Changes in walking pattern |
| Loss of balance | Increased risk of falls |
| Reduced reflexes | Decreased knee or ankle jerk reflexes |
| Muscle contractures | Loss of ability to move independently |
| Bone mass loss | Loss of calcium and other minerals |
| Height decrease | Due to thinning and shortening of vertebrae |
| Metabolic changes | Decrease in muscle protein synthesis |
| Type II muscle fiber decrease | Smaller and flatter fibers |
| Progressive resistance training | Can help rebuild and maintain muscle |
| High-protein diet | Recommended intake of 1 to 1.3 grams per kilogram of body weight |
| Leucine | An essential amino acid that helps build and repair muscle |
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What You'll Learn
Hormonal changes
The natural ageing process is associated with a variety of hormonal changes that may contribute to muscle loss. The primary and most potent anabolic steroid in the body is testosterone, which increases muscle protein synthesis, muscle mass, and strength. In about 60% of men over the age of 65, testosterone levels decrease to below the normal youthful values, in a process termed andropause. Unlike menopause, where oestrogen levels rapidly decrease, testosterone concentrations gradually decline throughout the ageing process. Thus, the decrease in testosterone may cause a decrease in muscle protein synthesis, resulting in a loss of muscle mass. Several studies have examined the effect of testosterone replacement therapy in men with low testosterone levels, but supplemental testosterone can have adverse effects and is not approved by the FDA for increasing muscle mass.
Hormone replacement therapy for menopause, adrenopause, or somatopause appears to have a marginal or no positive effect on muscle mass and strength. However, exercise training and proper nutrition can have dramatic effects on muscle mass and strength. An optimal intervention program may include an exercise-training schedule that incorporates both resistance and aerobic exercise with adequate intake of total calories and protein. This would not only improve muscle mass and strength but would also reduce insulin resistance, which is more prevalent in the elderly. Providing a nutritional supplement of only amino acids or protein might also be beneficial to promote muscle growth by stimulating muscle protein synthesis and increasing total daily caloric intake.
Recent research has identified a critical enzyme called "gerozyme" that becomes more abundant as we age. Gerozyme degrades prostaglandin-E2 (PGE2), a hormone-like substance and a key factor in muscle repair, reducing its abundance. When gerozyme was inhibited in aged mice, levels of PGE2 were boosted back to youthful levels, stimulating muscle stem cells to multiply and increasing energy stores, muscle mass, and strength. This discovery suggests the potential for developing a drug to increase muscle strength in humans.
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Motor neuron loss
Motor neurons are essential for translating synaptic inputs into motor functions. Ageing is associated with a net loss of these motor neurons, which leads to impaired motor performance. This loss of neurons is believed to be a primary cause of sarcopenia, the age-related loss of muscle mass and strength.
A 60-year-old has approximately 25-50% fewer motor neurons than a 20-year-old, with the greatest losses in distal fast-twitch motor neurons. This loss of neurons leads to a decrease in muscle fibre number and size, particularly Type II fast-twitch glycolytic fibres. As a result, muscle strength and power are reduced, and muscles become less toned and less able to contract.
The loss of motor neurons is due to a combination of denervation and reinervation of the muscle fibre throughout one's lifespan. With ageing, the rate of denervation outpaces reinervation, leading to a net loss of motor neurons. This can result in either permanent denervation of the muscle fibre or reinervation by a different motor neuron, potentially altering the characteristics of the fibre.
The breakdown in communication between the brain and muscle due to age-related changes in the nervous system can also contribute to muscle weakness and impaired performance. This includes changes in the central and peripheral nervous systems, as well as reduced cortical excitability, dopaminergic dysfunction, and arousal. Additionally, the loss of dopamine neurons with ageing can lead to neural noise, further impairing muscle performance.
To mitigate the effects of motor neuron loss, physical activity and progressive resistance training can be beneficial. These activities can modify motor unit properties and functions, helping to improve strength, balance, and flexibility. Additionally, a well-balanced diet with adequate protein intake and calcium intake is important for maintaining muscle health and preventing age-related bone loss.
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Exercise and diet
Exercise
Exercise is one of the most effective tools to slow down or prevent muscle ageing. Engaging in a moderate exercise program can help maintain strength, balance, and flexibility, while also keeping your bones strong. It is recommended to include both resistance and aerobic exercises in your routine. Progressive Resistance Training (PRT) is particularly beneficial for building muscle mass at any age. With PRT, you gradually increase the intensity of your workouts as your strength and endurance improve, challenging your muscles and preventing plateaus.
Diet
A well-balanced diet is essential for supporting muscle health. As we age, our bodies require adequate calories, protein, calcium, and vitamin D. A higher-protein diet can help rebuild and maintain muscle mass. Animal sources such as meat, eggs, and milk provide essential amino acids, but it's best to opt for lean meats to avoid high levels of saturated fat. A daily protein intake of 1 to 1.3 grams per kilogram of body weight is recommended for older adults doing resistance training. For example, a 175-pound man should aim for about 79 to 103 grams of protein per day, spread across meals to maximize muscle protein synthesis.
Additionally, calcium and vitamin D are crucial for bone health, especially for women after menopause and adults over 70. Ensuring sufficient calcium and vitamin D intake can help maintain bone strength and reduce the risk of fractures associated with muscle weakness.
Future Treatments
Research is ongoing to develop treatments for muscle loss. Dr Helen Blau's work has identified a critical enzyme, "gerozyme", that increases with age and breaks down prostaglandin-E2 (PGE2), which is key to muscle repair. Inhibiting gerozyme activity in mice boosted PGE2 levels, stimulating muscle stem cells and increasing muscle mass and strength. This discovery could pave the way for future drug treatments to combat muscle loss due to ageing, immobility, or injury.
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Insulin resistance
Skeletal muscle aging refers to the inevitable deterioration of skeletal muscle cell structure and biological function with age. This deterioration is characterised by decreased mitochondrial function, increased intramyocellular lipid, increased inflammation, increased oxidative and endoplasmic reticulum stress, weakened enzyme activities, decreased autophagic capacity, decreased muscle mass, and an over-activated renin-angiotensin system. These changes impair skeletal muscle insulin sensitivity and increase the risk of insulin resistance.
The changes in skeletal muscle mitochondrial structure and function are important features of skeletal muscle aging. Mitochondria become larger and rounder, mitochondrial density is reduced, and the number of mitochondria decreases. Additionally, there is an imbalance in mitochondrial fusion and fission during skeletal muscle aging.
The risk of insulin resistance can be reduced through weight loss and aerobic and resistive exercise training, which result in losses of total body fat and abdominal fat, and increase insulin sensitivity. Exercise training can also help prevent and treat insulin resistance and non-insulin-dependent diabetes mellitus. Progressive resistance training (PRT) is particularly effective in building muscle mass, as it gradually increases workout volume, weight, reps, and sets as strength and endurance improve.
A well-balanced diet is also important for maintaining muscle mass. A recent study suggests a daily intake of 1 to 1.3 grams of protein per kilogram of body weight for older adults who do resistance training. Animal sources such as meat, eggs, and milk are considered the best sources of protein, but it is important to avoid red and processed meat due to high levels of saturated fat and additives.
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Genetic factors
The speed and amount of muscle ageing seem to be influenced by genetic factors. Muscle changes often begin in men in their 20s and in women in their 40s. The majority of literature indicates that muscle fibre loss is due to a loss of motor neurons. There is consistent denervation and reinervation of the muscle fibre throughout one's lifespan, but in the aged, denervation appears to outpace reinervation.
Data indicates that a 60-year-old has approximately 25-50% fewer motor neurons than a 20-year-old, with the greatest losses in distal fast-twitch motor neurons. With the loss of the motor neuron, the denervated fast-twitch muscle fibres that were attached to it are either permanently denervated and undergo apoptosis, or are reinervated with a different motor neuron, most likely that of a slow-twitch neuron, potentially making the fibre take on slow-twitch characteristics.
At the cellular level, specific age-related alterations include a reduction in muscle cell number, muscle twitch time and twitch force, sarcoplasmic reticulum volume, and calcium pumping capacity. Sarcomere spacing becomes disorganized, muscle nuclei become centralized along the muscle fibre, the plasma membrane of the muscle becomes less excitable, and there is a significant increase in fat accumulation within and around the muscle cells.
Neuromuscular alterations include a decrease in the nervous firing rate to muscle, the number of motor neurons, and the regenerative abilities of the nervous tissue. Motor unit size also increases. Biochemical and metabolic changes also occur in muscle with ageing.
Furthermore, hormonal changes during the ageing process, such as the decrease in testosterone levels in men, can contribute to muscle loss. Testosterone is a potent anabolic steroid that increases muscle protein synthesis, muscle mass, and strength. The decline in testosterone levels with age may lead to a decrease in muscle protein synthesis and subsequent muscle loss.
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Frequently asked questions
Muscle ageing is the loss of muscle tissue and function that occurs as a natural part of the ageing process.
Muscle ageing is caused by a variety of factors, including hormonal changes, a reduction in muscle cell number, muscle twitch time and force, and changes in nerve function.
While muscle ageing is a natural part of the ageing process, it can be slowed or prevented through exercise, proper nutrition, and interventions such as testosterone replacement therapy.
Muscle ageing can lead to weakness, slowed movement, reduced balance and coordination, and an increased risk of falls and fractures.
Muscle ageing typically begins in the 20s in men and in the 40s in women. Men typically lose more muscle mass than women, with most men losing about 30% of their muscle mass during their lifetime.
