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Immobility, often caused by bed rest, has a significant impact on bone and muscle health. The effects of immobility are wide-ranging, from muscle atrophy and weakness to bone demineralization and osteoporosis. The musculoskeletal system is designed to allow the body to move and carry out daily activities, so when a person becomes immobile, the resulting muscle weakness and joint stiffness can greatly impact their quality of life. The longer the period of immobility, the more severe the consequences, with rapid reductions in muscle mass, bone mineral density, and other body systems occurring within the first week of bed rest.
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What You'll Learn
Muscle wasting occurs within 10 days of immobility
Muscle wasting or atrophy occurs when there is an imbalance between protein synthesis and protein degradation. It is a natural consequence of aging called sarcopenia. While sarcopenia is gradual and varies from person to person, it can be accelerated by malnutrition, immobilization, or certain diseases.
Disuse or physiologic atrophy occurs when muscles are not used enough. This can be due to injury, illness, bed rest, or a sedentary lifestyle. The rate of muscle atrophy from disuse ranges from 0.5% to 0.6% of total muscle mass per day, with the elderly being the most vulnerable to dramatic muscle loss. Research indicates that muscle atrophy occurs after three or four days of immobilization, with the process starting within two to three weeks of muscle disuse. Within 10 days of immobility, muscle wasting can be accelerated by malnutrition, with fat loss progressing to muscle atrophy.
The muscles most affected by immobility are the antigravity muscles that facilitate locomotion and assist in maintaining an upright position (quadriceps, glutei, erector spinae, and gastrocnemius-soleus muscles). Generally, 10-15% of muscle strength is lost each week, with up to 5.5% lost for each day of immobility. The greatest loss of strength occurs during the initial period of inactivity, with bed rest for 4-5 weeks resulting in a 20-25% decrease in lower-limb extensor muscle strength.
To prevent and treat muscle wasting, adequate nutrition and exercise are crucial. Resistance or resistive exercise has been shown to reduce muscle atrophy, especially in older adults. Additionally, a healthy diet with sufficient protein intake can help prevent muscle loss. β-Hydroxy β-methylbutyrate (HMB), a dietary supplement, has been effective in preventing muscle mass loss in several muscle-wasting conditions.
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Bones lose density and become fragile
Bones provide mechanical support for body tissue and muscles, as well as maintaining mineral homeostasis by providing a reservoir of calcium, phosphorous, and magnesium salts. When the body is exercising, osteoblasts and osteoclasts work at a similar rate, maintaining general bone density. However, during periods of immobility, the mechanical loading of the skeleton is reduced, resulting in a decline in osteoblasts, which are responsible for building the bone matrix. This causes a reduction in bone synthesis, while osteoclasts continue to break down bone tissue, leading to a loss of bone density.
This loss of bone density leaves bones fragile and at risk of fractures. The decrease in gravitational forces superimposed on bones during bed rest leads to bone demineralization and a loss of trabeculae volume. Bones become thin, porous, and fragile due to increased osteoclastic activity and greater resorption of bone. Bone loss can occur as early as the third day of immobilization, and the risk of fractures is particularly high in the hip, spine, and extremities. The elderly are especially vulnerable to bone loss from immobility due to the compounding effects of age-related osteoporosis.
To prevent bone loss, rehabilitative treatments focus on increasing muscle strength, mobility, and ambulation as soon as possible. Restoring weight-bearing forces is crucial for maintaining bone mass and reversing bone loss. Early standing, ambulation, and muscle-strengthening programs assist in preventing bone wasting. Isotonic and isometric contractions, such as ambulatory exercise, have been found to restore bone minerals. Preventative measures include early mobility and respiratory muscle training, which can help mitigate the severity of bone loss during immobilization.
The rate of muscle wasting and bone loss varies depending on the duration of immobility and individual factors. Muscle atrophy and muscle strength losses occur rapidly with prolonged bed rest, with significant decreases in muscle mass and size. Within the first week of bed rest, rapid reductions in bone mineral density are evident, alongside muscle wasting and weakness. Muscle wasting can occur within 10 days in healthy older adults, and the greatest loss of muscle strength tends to occur during the initial period of inactivity. Inactivity can cause a significant decline in muscle endurance, with antigravity muscles being the most affected.
Overall, immobility leads to a loss of bone density, resulting in fragile bones susceptible to fractures. Preventative and rehabilitative measures focus on restoring weight-bearing forces, increasing muscle strength, and promoting early mobility to mitigate bone loss and its associated complications.
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Muscle atrophy is the most obvious side effect of long-term bed rest
The rate of muscle wasting varies depending on the individual and the specific muscles affected. In general, 10-15% of muscle strength is lost each week, but this can be as high as 5.5% per day of immobility. The greatest loss of strength occurs during the initial period of inactivity, with bed rest for 4-5 weeks resulting in a 20-25% decrease in the strength of lower-limb extensor muscle groups. The first muscles to atrophy are typically those in the lower limbs that normally resist gravitational forces when in an upright position.
The impact of bed rest on muscle metabolism has been studied, with research showing that lipid overload in muscles leads to lipotoxicity and inflammation. Long-term bed rest also results in internal mitochondrial alterations. Exercise interventions, including resistive exercise, resistive vibration exercise, and treadmill exercise, have been found to attenuate loss of muscle mass. However, even with exercise intervention, high rates of bone loss have been observed.
The effects of immobility on the musculoskeletal system can be severe and may require rehabilitative treatment. Restoring weight-bearing forces is crucial for maintaining bone mass and reversing bone loss. Early standing, ambulation, and muscle-strengthening programs can assist in preventing bone wasting. Additionally, respiratory muscle training can help prevent the weakening of chest wall muscles and potential respiratory complications.
Overall, muscle atrophy is a significant and visible consequence of prolonged bed rest, leading to a decline in muscle mass, strength, and function. The impact of immobility on the musculoskeletal system can be mitigated through early intervention and appropriate rehabilitative measures.
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The immobile body loses calcium from bones
The human body is designed for movement, and when it is rendered immobile, several changes occur, including bone and muscle wasting. The immobile body loses calcium from bones, leading to a decrease in bone density and an increased risk of osteoporosis.
Bone health is maintained by osteoblasts and osteoclasts, which work to build and break down bone tissue, respectively. When the body is active, these two processes occur at roughly the same rate, maintaining bone density. However, during immobility, the mechanical loading of the skeleton is reduced, resulting in a decline in osteoblast activity and an increase in osteoclastic activity. This imbalance leads to a loss of calcium from the bones, causing them to become thin, porous, and fragile.
The loss of calcium from bones during immobility can predispose individuals to fractures, especially in the hip, spine, and extremities. Elderly individuals are particularly vulnerable to the effects of immobility due to the combined impact of inactivity and age-related bone loss, such as osteoporosis.
To prevent bone loss and maintain bone health during periods of immobility, early mobilisation and rehabilitative exercises are crucial. Restoring weight-bearing forces through standing, walking, and muscle-strengthening programs can help maintain bone mass and reverse bone loss. Additionally, early intervention with appropriate exercises can mitigate the severity of immobilization-induced bone wasting.
While immobility can lead to bone and muscle wasting, proactive measures such as early mobilisation and targeted exercises can help mitigate these negative effects and support overall bone health.
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Muscle weakness and atrophy affect the respiratory system
Muscle weakness and atrophy have a significant impact on the respiratory system. The respiratory system relies on the muscles to facilitate breathing and gas exchange. When these muscles weaken or waste away, the respiratory system's ability to function is impaired. This can lead to respiratory failure, which is a life-threatening condition.
Muscle weakness and atrophy can affect the respiratory muscles directly. For example, the external intercostal muscles in patients with chronic obstructive pulmonary disease (COPD) may undergo similar cellular changes as other muscles affected by the disease. In advanced COPD, biological mechanisms affecting the lower limbs, such as injury, oxidative stress, and enhanced proteolysis, prevail over the adaptive mechanisms in the respiratory muscles.
The impact of muscle weakness and atrophy on the respiratory system is particularly evident in patients with muscular dystrophy, a group of inherited myopathies characterised by progressive skeletal muscle wasting, including the respiratory muscles. Respiratory failure in muscular dystrophy patients is often due to lung failure or pump failure. The respiratory pump, composed of respiratory muscles, moves air into the lungs by overcoming the elastic and resistive forces exerted by the chest wall and lungs. When these muscles weaken, the respiratory pump's ability to generate pressure is compromised, leading to ventilatory failure.
Additionally, muscle weakness and atrophy can indirectly affect the respiratory system by causing a decrease in physical activity. Reduced physical activity can further deteriorate muscle function and mass in patients with respiratory conditions. This creates a vicious cycle where muscle weakness leads to decreased physical activity, which in turn exacerbates muscle dysfunction.
The consequences of muscle weakness and atrophy on the respiratory system are serious and can lead to increased morbidity and mortality rates. Preventive measures, such as early mobility and respiratory muscle training, are crucial to mitigate these negative effects.
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Frequently asked questions
Immobility is when a patient’s movement is restricted. This can be purposeful and temporary, such as when a patient is immobilized to promote healing due to a broken bone, or it can be the result of a pathologic condition, like a stroke.
Immobility causes muscle wasting by reducing muscle mass and size. The greatest loss of strength occurs during the initial period of inactivity. The antigravity muscles that facilitate locomotion and assist in maintaining an upright position (quadriceps, glutei, erector spinae, and gastrocnemius–soleus muscles) are the most affected by immobility.
Immobility causes bone wasting by reducing bone mass and density. With bedrest, there is a decrease in the gravitational forces superimposed on bones, which leads to bone demineralization and a loss of bone density. Bones become thin, porous, and fragile, leaving patients at risk of fractures.
