Muscle Function: Effects of Aging


Human muscles.jpg

As we age our muscles undergo progressive changes, primarily involving loss of muscle mass and strength.

The age-related loss of muscle function is known as Sarcopenia[1], derived from the Greek words for flesh (sarcos) and loss (penia) and its definition includes loss of muscle strength and power, as well as reduced function[2]. It occurs with increasing age, and is a major component in the development of frailty.

The loss of muscle mass during the aging process is important clinically as it reduces strength and exercise capacity, both which are needed to perform activities of daily living. The video below gives a good summary of the changes and effects on performance and health.


Age-related Changes in Muscle Structure

With increasing age, we lose muscle mass: lean muscle mass contributes up to 50% of total body weight in young adults, but this decreases to 25% by 75 to 80 years[4]
Typical muscle changes with age:

Gross Muscle changes:

Reduced muscle mass (replaced by increased fat mass)

Reduction in lower limb muscle cross-sectional area have been observed to begin in early adulthood and accelerate beyond 50 years of age.This reduction in muscle cross-sectional area associated with decreases in contractile structures accompanied by increases in non contractile structures such as fat and connective tissue.[5]

Reduced muscle strength

The total number of muscle fibers is significantly reduced with age, beginning at about 25 years and progressing at an accelerated rate thereafter The decline in muscle cross-sectional area is most likely due to decreases in total fiber number, especially type II fast-twitch glycolytic fibers. This results in reduced muscle power.[5]

Muscle Fibre changes:

Changes in Muscle Fiber Size

Elderly individuals often fall because of poor muscle strength and reduced balancing ability related to muscle aging. Types IIA and IIB muscle fibers decrease with age in the area percentage, fiber number percentage, and mean fiber area, whereas Type I fibers increase in area and number but not in size. Morphologically, Type II fibers appeared smaller and flatter. Investigations suggest deterioration in muscle quality and balancing coordination in elderly patients. A research done provided data to help determine treatments for reversing muscle fiber changes and reducing the number of falls and related fractures in patients.[6]The reduction in number of muscle fibers contributes more to the decrease of whole muscle cross-sectional area than does the reduction in area of individual fibers. The individual fast-twitch type II fibers decrease in cross-sectional area suggest that the relative contribution of fast-twitch type II fibers to force generation is less in the older adult.

Motor Unit Number and Size

The majority of the literature indicates that muscle fiber loss is due to a loss in motor neurons. There is consistent denervation and reinervation of the muscle fiber throughout one’s lifespan, but in the aged, denervation appears to outpace reinveration. Data indicate 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 deinervated fast twitch muscle fibers that were attached to it are either permanently deinervated and undergo apoptosis, or are reinverated with a different motor neuron most likely that of a slow twitch neuron, potentially making the fiber take on slow twitch characteristics[7]

Effects of Endocrine Changes on Muscle

With increased age, the following changes in endocrine function result in sarcopenia:

  • Increased insulin resistance[8]
  • Decreased growth hormone[9]
  • Reduction in oestrogen and testosterone[10]
  • Vitamin D deficiency[11]
  • Increased parathyroid hormone[12]

Conditions Associated with Impairment of Skeletal Function

Functional Effects of Sarcopenia

Sarcopenia has a marked effect on function in all activities of daily living, contributing (along with reduction in balance) to reduced gait speed, falls, and fractures. The combination of osteoporosis and sarcopenia results in the frailty which frequently occurs in the elderly population.

Physiotherapy Interventions to Minimise or Reverse Sarcopenia

Resistance exercise training :

The effects of resisted exercise on ageing muscles is the same as for young muscles:

  • improved muscle strength
  • increased muscle power - power is a product of both strength and speed. Optimal power reflects how quickly you can exert force to produce the desired movement
  • improved muscle composition


Population studies

Resistance or weight training has been demonstrated to produce increases in muscle strength and power, and also mobility function, in older people living in the following settings:

  1. independently in the community[13][5][14]
  2. in nursing homes[15][16]
  3. hospitalised elderly people[17][18]

Gender differences

Increased muscle quality from resistance training is a common finding in older adults, and in men there appears to be no difference in young versus old[19], but there is a study which suggests that older women have a blunted response relative to younger women[20].

Frequency of resistance training

Studies have demonstrated that resistance training regimes performed once, twice or even three times a week all result in strength improvements[14].

Length of training programme

There are many studies which clearly demonstrate that older people who participate in resistance training programs lasting at least 6 to 12 weeks will show increase in both strength and mobility function[21][22][23].

Cochrane Review

The authors collated the results from 121 RCTs examining the effects of resistance strength training exercises, and came to the following conclusions:

"This review provides evidence that PRT (Progressive resistance strength training) is an effective intervention for improving physical functioning in older people, including improving strength and the performance of some simple and complex activities. However, some caution is needed with transferring these exercises for use with clinical populations because adverse events are not adequately reported."[24]

Dietary Advice

The Society for Sarcopenia, Cachexia, and Wasting convened an expert panel to develop nutritional recommendations for sarcopenia prevention and management.This panel concluded that for preventing and treating this condition, protein and energy intake are key components, along with both resistance and aerobic exercise.

Is there a role for supplements?

There is some evidence suggesting that additional supplementation with the amino acid Leucine (or its metabolite HMB) could potentially increase the effects of resistance training to combat sarcopenia[25][26].



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