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Bone and Muscles

  • Reiner Bartl
  • Christoph Bartl
Chapter
  • 928 Downloads

Abstract

A reduction of muscle and bone mass and an increase in fat mass are characteristic changes in increasing age. The term “sarcopenia” includes an age-related loss of muscle mass and muscle strength. Muscle loss also significantly contributes to the development of various metabolic and mechanical geriatric syndromes (e.g., diabetes type 2). Sarcopenia develops from the age of 35 years and leads above all to a decline in type II muscle fibres and an increase of intramuscular lipids. The skeletal muscle also produces various growth factors (IGF-1 and MGF), which have an anabolic effect on the skeleton and also support fracture healing. These “myokines” are above all demonstrably increased by muscle building training. In contrast, during physical inactivity and muscular atrophy, myostatin, a negative regulator of muscle mass, leads to muscle loss. Other factors that lead to a decrease in muscle strength and muscle mass include cachexia, AIDS, smoking, protein and vitamin D deficiency, chronic inflammatory processes (e.g. COPD) and glucocorticoids. In addition to sarcopenia, intramuscular lipid, “myosteatosis”, increases with age and increasing body fatness.

Keywords

Muscle mass Muscular atrophy Muscle loss Chronic inflammatory process Increased bone density 

92.1 Sarcopenia and Bone Mass

A reduction of muscle and bone mass as well as an increase in fat mass are characteristic changes in increasing age. The term “sarcopenia” includes an age-related loss of muscle mass and muscle strength.

Sarcopenia is the age-related loss of skeletal muscle mass with concomitant decrease in muscle strength leading to a reduction in physical activity, which, with advancing age, is a major cause of osteoporosis, falls, fractures, immobilisation and other disabilities. Sarcopenia is internationally recognised as a major feature of human senescence.

Muscle loss also significantly contributes to the development of various metabolic and mechanical geriatric syndromes (e.g. diabetes type 2). Sarcopenia develops from the age of 35 years and leads above all to a decline in type II muscle fibres and an increase of intramuscular lipids. The skeletal muscle also produces various growth factors (IGF-1 and MGF), which have an anabolic effect on the skeleton and also support fracture healing. These “myokines” are above all demonstrably increased by muscle building training. In contrast, during physical inactivity and muscular atrophy, myostatin, a negative regulator of muscle mass, leads to muscle loss. Other factors that lead to a decrease in muscle strength and muscle mass include cachexia, AIDS, smoking, protein and vitamin D deficiency, chronic inflammatory processes (e.g. COPD) and glucocorticoids. In addition to sarcopenia, intramuscular lipid, “myosteatosis”, increases with age and increasing body fatness.

The skeletal muscle mass correlates closely with bone mass and the corresponding age-related muscle loss goes hand in hand with bone loss and an increased risk of fracture in old age.

The loss of skeletal muscle and bone mass with advancing age is closely related. Therefore bone density and skeletal muscle mass are the primary risk factors of fractures. This relationship is seen in children, adults, men and women.

In addition the fracture risk is increased by the greater tendency to fall in old age. A targeted muscle training with elderly, hospitalised and immobilised people is most important, regardless of age and gender. On the one hand, muscle building leads to increased bone density and on the other hand to a minimised risk of falling and to a reduced fracture risk.

92.2 Muscle Training and Bone Mass

The positive effect of physical activity on bone mineral density and fracture risk is well documented. In older women, a weekly programme of exercise increases bone density and reduces the tendency to fall as well as the risk of fracture. It should be considered that certain training exercises, such as endurance sports, cycling, continuous running or swimming, can lead to a reduction in bone density. All movements that are directed against the force of gravity, e.g. power sports (weight lifting) and sprint training, are worthwhile. The explanation for this seemingly paradoxical behaviour of the muscles is found in the microscopic structure of the muscles.

There are two types of muscle fibres, which are more or less equally distributed in most people:
  • Red muscle fibres (type I, ST): slowly working, fatigue-resistant fibres

  • White muscle fibres (type II, FT): fast working with short-term, high-power and quickly tiring

Both types of muscle fibre are active at each training session. Depending on the type of activity, different fibre types are dominant. Thus, the muscles of the sprinter Carl Lewis are supposed to have consisted of up to 90% white muscle fibres. According to the type of sport, the two types of fibre can be specifically trained and strengthened:
  • Light jogging, walking, cycling and swimming train above all the slow muscle fibres, which contributes little to the skeletal system.

  • Speed and power training and weightlifting strengthen mainly the fast muscle fibres with particularly pronounced benefits for the skeletal system.

Vibration training is an interesting development to strengthen muscles and bones. A platform with vibrations of >32 Hz stimulates, above all, the muscle fibres type IIa and thereby the bone structure. The platform is recommended for immobile elderly people as well as people with Parkinsonism, multiple sclerosis, rheumatism and muscle weakness. Higher frequencies have the advantage that disruptive vibrations of the body are avoided.

Muscle and bone mass are correlated and form a functional unit! Strengthening the muscles is the most important preventive measure for the prevention of osteoporosis! At the same time, improving coordination is another important factor for prevention of fractures. Vibration training to strengthen the muscles is useful for people with restricted mobility.

92.3 Immobilisation Osteoporosis

Insufficient physical activity and thereby muscle loss is one of the most important risk factors for osteoporosis. This applies especially to younger bedridden patients, who, within a few months, can lose bone and muscle mass up to 30% and then need years to restore the original bone density. If, for example, an arm is immobilised after a fracture in plaster for 3 weeks, the affected bones lose up to 6% of their density. A study on bedridden patients showed that the trabecular bone decreases by an average of 1% per week. This is true especially for bedridden children. On the commencement of physical activity, the bone mass regenerates at 1% per month, so that the recovery of bone mass is considerably slower than the bone loss during immobilisation. Examples of immobilisation with rapid bone loss are:
  • Paralysis after spinal cord injury

  • Hemiplegia after cerebrovascular events

  • Paraplegia of the lower half of the body

  • Myopathies and polyneuropathies with muscle weakness

  • Immobilisation after fractures of the lower extremities in children

  • Immobilisation from multiple sclerosis

92.3.1 Paraplegia

The bone loss after a spinal cord injury can be so pronounced that the smallest force might cause fractures (e.g. during the transfer to a wheelchair or putting on support stockings). After 1 year, you can already find an osteoporosis in the femur neck of 42% of paraplegics. The spasticity that occurs in most patients with spinal cord injuries has in comparison to patients with flaccid paralysis a significant positive effect on bone density. An early start to training, standing upright together with a passive treadmill exercise has a positive influence on bone mass.

92.3.2 Myopathies and Polyneuropathies with Muscle Weakness

An example is myasthenia gravis, an autoimmune disease with episodic muscle weakness, which leads to systemic and local osteoporosis, due to reduced bone load wearing and the commonly used glucocorticoid therapy. Regular monitoring of bone density using DXA method is advisable.

92.3.3 Bed Confinement

Patients with osteoporosis, who because of a fracture were bedridden for several weeks, suffer from frequent fractures during the subsequent period of mobilisation. The time of postoperative bed rest should be, through use of new surgical techniques, as short as possible, and the bones should be protected against bone loss by application of effective medication (bisphosphonates).

92.3.4 Loss of Gravity

Astronauts must perform a special and regular muscle training due to the absence of gravity in the outer space. Nevertheless, they lose about 1% of their bone mass per month. Under space conditions, astronauts experience a ten times higher bone loss than earthbound patients with osteoporosis. The bone loss in astronauts was examined in detail and today serves as a model for immobilisation osteoporosis.

Three mechanisms were detected under zero gravity conditions, which also play an important role in the emergence of osteoporosis on earth:
  • Demineralisation of bone substance

  • Inhibition of osteoblast activity

  • Activation of osteoclasts

Therapeutically, an increased physical activity, targeted gymnastics and an early functional treatment are recommended. Weight and resistance training methods, such as the Theraband, are beneficial for immobilised patients in bed. While bone loss in children and young people can quickly rebuild, with older adults bone recovery can often take many years. As a rule, the bone density levels at the start of the immobilisation phase are not regained. Dependent on the results of the bone density measurement, preventive medication in the form of an early application of oral BP comes into use. A BP therapy must be initiated on the basis of osteoporotic results. As a massive bone loss occurs shortly after the onset of paralysis due to the missing load on those bones, a higher i.v. BP therapy should be considered. Options are as follows:
  • Alendronate 70 mg weekly

  • Risedronate 35 mg weekly

  • Ibandronate 3 mg injection per 3 month

  • Zoledronate 5 mg infusion per year

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Reiner Bartl
    • 1
  • Christoph Bartl
    • 1
    • 2
  1. 1.Osteoporosis and Bone CenterMunichGermany
  2. 2.Center of Orthopaedics and Sports MedicineMunichGermany

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