The causes of osteoporosis are multiple. It has been shown that the stresses on the bone itself and the various stresses generated during muscle contraction have a very important effect on bone quality. Dr. Frost (USA) clearly states that muscle mass (including mass and force of the muscle mass) under the control of the nervous system is an important factor in determining bone strength. This muscle-generated force (called mechanical factors) controls bone strength much more than non-mechanical factors (including various bone-related hormones, vitamins, calcium and other minerals, amino acids, fats, bone-related cytokines, etc.).
Structural and mechanical properties of bone tissue in osteoporosis
Osteoporosis is a systemic degenerative lesion of the skeletal system characterized by a reduction in bone mass and destruction of bone microarchitecture. The reduction in bone mass and bone quality reduces the physical properties (mechanical strength) of bone tissue and increases the susceptibility to fracture.
Bone “quantity” and bone “quality” are two different concepts, the former refers to the quantity or volume of bone, while the latter refers to the microstructure of bone, mineralization of bone matrix, bone transformation, and the accumulation of microfractures and their repair capacity. Physical properties such as bone strength, elastic modulus and stiffness depend on both quantitative and qualitative components of bone.
Bone quantity: The total amount of bone in patients with osteoporosis is significantly reduced, but the rate of bone loss is not the same for each site, with bone loss in cancellous bone occurring earlier than in cortical bone and bone loss in trunk bone (spine) being more severe than in limb bone. Bone loss also differs between age groups, with the older the age, the more bone loss and the lower the bone mass. In women, bone loss accelerates starting in the perimenopause, and bone loss occurs earlier than in men, with a higher rate of loss than in men. In osteoporosis, the number of bone trabeculae per unit volume decreases and the cortex becomes thinner. In addition, bone volume at different sites is also related to the stress load on that site, and sites with high load have high bone volume and bone density.
Currently, bone volume is usually measured by dual-energy X-ray bone mineral absorptiometry (DEXA), which uses measured bone mineral density (BMD) values or bone mineral content per unit area (BMC) to express bone volume. This method uses the density of bone mineral salts content and distribution in the bone matrix (cancellous and cortical bone) to reflect bone mass values, making bone mass measurable.DEXA has a high accuracy and correctness of measurement and is a more objective and reproducible means of measuring bone mass, which can be used to diagnose osteoporosis, indirectly reflect bone strength and predict fracture risk, while dynamic observation can also show the rate of bone loss. A decrease in BMD implies a decrease in bone strength and an increase in the risk of fracture. BMD values in patients with osteoporosis depend both on their peak bone mass in youth, i.e. bone reserve, and on the rate of bone turnover in old age or menopause, i.e. the rate of bone loss.
Bone mass: bone is a hydroxyapatite crystalline composed of 90% type I collagen and 10% non-collagenous protein. The basic structure of collagen is a triple helix structure consisting of 2 alpha1 and 2 alpha2 polypeptide chains of aminoacetic acid, proline, and hydroxyproline. Osteogenic collagen is secreted by osteoblasts into the intercellular space and mineralized to form the microstructure of bone. The quality of bone is composed of five factors: the microarchitecture of bone tissue, the collagen composition of bone, the mineralization of the matrix, the transformation of bone, and the accumulation of microfractures and the ability to repair fractures. The microarchitecture of bone contains factors such as trabecular thickness, density, spatial arrangement and inter-trabecular connections, especially the number and mechanical configuration of the connective trabeculae are important for the load-bearing capacity of bone. Bone matrix proteins (collagen) give bone its toughness, mineralization of the matrix gives bone its stiffness, and the bone matrix mineral salt content determines bone stiffness and elasticity.
During biological evolution, bone tissue acquired physical properties such as stiffness, elasticity and energy absorption. Variations in bone size and morphological structure are determined by genetic codes that can be modified by stress and other environmental factors that affect the bone during growth and development and adulthood. Early in growth and development, the skeleton is most sensitive to stress loading, and the skeleton responds to stress by altering morphology, volume and structure to complete bone building to accommodate the load. Bone tissue is mineralized collagen tissue located between the endosteal and eposteal membranes, and bone tissue itself is constantly renewed and modified. During the process of bone remodeling, bone morphology and its three-dimensional spatial construction are regulated by biological and mechanical laws, in accordance with Wolff’s law.
The body’s own gravity is a reaction force of the same magnitude generated by gravity acting on the body, which has a hydrostatic effect on the growth, development, and formation of the structure of the human scaffold (skeletal system), while the stresses of movement and labor have a kinetic effect on the bone. Taller, heavier people have greater bone volume and bone mass than shorter, thinner people, and the density of bone is also relatively high. Those who enjoy sports and engage in physical labor have greater bone volume and bone mass than non-participants. The occurrence of osteoporosis is not only related to the loss of bone volume and bone quality due to the biological degeneration of bone tissue with aging, but also to the changes in the internal and external mechanical environment caused by the structural degeneration and functional decline of the locomotor and nervous systems that occur simultaneously with aging. Changes in the mechanical environment can accelerate and promote the process of biological degeneration of bone tissue. Bone growth and development up to its peak is the stage of accumulation of bone mass, followed by a period of relative bone metabolic equilibrium, and then by a stage of bone loss with increasing age. The process of bone tissue remodeling, reconstruction and bone structure characteristics at each stage essentially reflect the biological effects of bone tissue on mechanical effects at different stages.
The role of muscle on bone and the relationship with osteoporosis
Bone and muscle and other motor systems are the basis of movement, and muscle, as one of the most adjacent tissues of the skeleton, is the link between bone and bone connection, and is closely related to bone growth and development. Muscle is the engine of human movement, producing movement is the basic function of muscle, in addition, muscle also has the function of support, maintaining posture, etc.
1.The role of muscle in bone metabolism
The mechanical load generated by the contraction of the muscle attached to the bone surface acts on the bone to produce strain, which then acts on the osteoblasts and osteoclasts, which becomes the main factor regulating bone reconstruction. When people reach old age, their muscle strength (especially explosive force) decreases and their activity decreases, resulting in a lower level of stress in the bone, while bone structure and bone volume depend on the magnitude of stress in mechanics. In essence, this stress is a biomechanical coupling of bone resorption and bone formation. Bone structure and bone mass are regulated primarily by mechanical loading generated by muscles, and this mechanical loading effect, together with the strain generated by the bone, is an important stimulus for osteoblasts to continuously form new bone in situ, thereby increasing bone mass. Once this stimulus is weakened, it can both increase bone resorption and reduce bone formation, eventually forming osteoporosis.
2, muscle and bone density bone mineral content
Studies have shown that weight bearing and exercise are an important mechanical stimulus for bone growth and reconstruction, both of which can increase bone mineral density (BMD) and BMC. human movement is produced by muscle contraction, and muscle has the closest relationship with BMD and BMC, both univariate and linear. The effect of muscle strength on BMD is more significant than the effect of muscle content on BMD. The effect of muscle on BMD is caused primarily by dynamic loading, i.e., muscle strength, and secondarily by static loading, i.e., gravity generated by the muscle itself. The decrease in bone mass, especially in the spine and lower extremities, is the result of the reduced action of mechanical stress on bone produced by muscle contraction. Increasing muscle strength through exercise can promote higher BMD.
3.Muscle and osteoporotic fracture
Falls are a major risk factor for osteoporotic fractures. Muscle is not only directly related to BMD and BMC, but also an independent indicator of postural stability, which plays a decisive role in postural balance and stability. Low BMD and poor stability both increase the frequency of falls. Osteoporosis and degenerative loss of functional muscle units in the elderly promote deformation of osteoporotic bones, in addition to decreased physical work, which affects muscle and bone health and causes disproportionate weakness of the back extensor or flexor system relative to body weight, increasing the risk of compression fractures of sparing vertebrae. The best measure to prevent falls and fractures due to decreased bone mass in older adults is to increase muscle strength, tension, and improve maintenance of muscle flexibility and strength through exercise. Exercise not only increases bone health, increases muscle strength, flexibility and body coordination and balance, and moves the body toward an overall healthy state, it is also the best form of strengthening bone formation and muscle support for bone.
In short, muscle has a close relationship with osteoporosis. Muscles not only affect bone metabolism, promote osteogenesis by contracting to produce stress, increase BMD and BMC, and improve osteoporosis, but also reduce the incidence of falls by increasing body balance and stability, which in turn reduces the incidence of fractures in osteoporotic patients.
The role of exercise on osteoporosis
A large number of studies have shown that exercise is not only a basic condition for bone mineralization and bone formation, but also promotes the secretion of sex hormones, regulates the metabolic state of the whole body, significantly improves muscle and nerve function, promotes the anabolism and reconstruction of bone and muscle, enhances bone strength and muscle strength, thus reducing bone loss and achieving the purpose of preventing and treating osteoporosis. In addition, adhering to appropriate physical exercise helps to improve and enhance the compliance, extension and flexibility of tendons and ligaments, improve balance and agility, thereby preventing or reducing the chance of falls and reducing the incidence of osteoporotic fractures.
The principle of exercise to prevent and treat osteoporosis
1, the stress effect of exercise: the efficacy of exercise to prevent osteoporosis lies in its stress effect on bone and the good effect on neuromuscular metabolism, etc.. Specifically expressed in.
① The muscle tension and mechanical stress generated by exercise acts on the bone, leading to specific deformation of bone tissue, changing the piezoelectric potential in the bone, which in turn stimulates osteoblast generation, promotes bone formation and reconstruction to maintain bone mass or increase bone density, and increases the elasticity of the bone, and increases the resistance to bending, extrusion and torsion. Studies have demonstrated that in postmenopausal women and the elderly, exercise compensates to some extent for the large loss of bone mass and thus plays a role in maintaining bone mass levels.
②The muscle contraction produced by dynamic and static exercise can keep the muscle nerve cells excited for a longer period of time, improve the working ability of nerve cells, enhance the issuance of nerve impulses, and increase the content of myoglobin and make the muscle thicker and increase the muscle strength.
2, the hormonal effect of exercise: endocrine plays a very important role in maintaining normal bone metabolism, mainly to promote the protein synthesis of bone, so that the total amount of bone matrix increases, and is conducive to bone calcification. In particular, testosterone and estradiol can promote the growth and development of bones, thicken the bone cortex and increase bone density.
Exercise can promote bone formation by regulating endocrine function, and can increase the secretion of testosterone and estrogen to promote bone metabolism.
3, the calcium effect of exercise: the calcium effect of exercise can be shown in: one, exercise can improve the threshold of calcium demand and promote the absorption of calcium. Exercise increases bone mass and also increases the demand for Ca, which raises the threshold of calcium requirement. On the contrary, when there is no exercise for a long time such as bed rest or limb immobilization, the demand for Ca in the bone pile is low and a large amount of Ca is excreted from the urine, thus decreasing the bone density. Second, when outdoor activities are performed, they can receive sufficient sunlight, which increases the vitamin D content and thus promotes Ca absorption. Third, proper exercise can improve the blood supply to bone tissue, thus promoting the absorption of Ca.
4, the muscle effect of exercise: the enhanced muscle strength of exercise also increases the level of bone mass. frost believes that in the pathogenesis of osteoporosis, the muscle mass (including muscle mass and muscle strength) under the regulation of the nervous system is an important factor in determining bone strength (including bone mass and bone structure). It has been found that muscle strength corresponds to bone volume in a roughly constant proportional relationship in humans, and age-related bone loss in women is often accompanied by a corresponding decrease in muscle strength. Because exercise increases muscle size and muscle strength, exercise increases muscle strength while maintaining or increasing the corresponding bone mass.
The way of exercise to prevent and treat osteoporosis
1.Exercise program
Although high-intensity and explosive sports stimulate the bones with great stress, this type of sports brings adverse effects on the patient’s circulatory system on the one hand; on the other hand, it is prone to fracture when repeatedly subjected to high stress. Therefore, high-intensity, explosive exercise is not recommended in the prevention and treatment of osteoporosis, especially for the elderly or osteoporosis patients should be contraindicated. The American College of Sports Medicine recommends the “osteoporosis prevention exercise program” is strength training and aerobic exercise.
Aerobic exercise: Commonly used exercise programs include walking, jogging, bicycling, swimming, stair climbing, hiking, dancing and various boxing exercises.
Walking: is the most simple and effective aerobic training activities, can be suitable for the elderly and frail. Walking speed should be moderately fast, the whole body relaxed, each time for 15-30 minutes.
Jogging: its exercise intensity than walking, jogging requires most of the muscles of the body to coordinate the completion. In the jogging should pay attention to: the heel first landing, and then the whole foot on the ground, so that the leg muscles can be relaxed. In addition, the knee joint should be slightly bent after the foot landing to cushion part of the force. The body posture should be correct, head up, chest up, both upper limbs relaxed and swing freely back and forth. Running should be coordinated with breathing, such as running 2~3 steps with one exhale and 2~3 steps with one inhale. The speed of running should also be mastered, so that the heart rate increases to the required level, and then maintain 15-30 minutes. The road for running should be wide and flat, and avoid exercising on too hard a sports ground to avoid sports trauma.
Strength exercise: abdominal muscles, back muscles, quadriceps exercises available barbell, dumbbells, sandbags, pulleys, special muscle trainers, their own body weight such as in situ jumping high resistance training, can also be used isometric training.
2.Exercise volume
After determining the exercise program, mastering the appropriate amount of exercise is the key to determine the effectiveness of exercise prevention. Exercise volume refers to the total amount of muscle work done in one exercise. Its size is influenced by three factors: intensity, duration and frequency of exercise, and the relationship between them can balance each other.
Exercise intensity: the elderly advocate low-energy exercise training, to 60% to 70% of the maximum heart rate is appropriate.
Exercise time: For general aerobic exercise, the duration can be a little shorter if the exercise intensity is high, and a little longer if the exercise intensity is low. Generally 30 minutes to 1 hour.
When using the same amount of exercise, young and fit people, it is appropriate to use the program of greater intensity and short duration; middle-aged and elderly people and frail people should choose the program of less intensity and longer duration. In short, the choice of exercise size should vary from person to person and should be decided according to the patient’s response and treatment effect.
Exercise frequency: that is, the number of exercises per week. If the amount of exercise is small, it can be 1 time per day or 1 time every other day; if the amount of exercise is large, the time interval should be slightly longer. However, it should be noted that if the interval exceeds 3 to 4 days, the accumulative effect of exercise disappears, the therapeutic effect will be reduced or ineffective. Exercise frequency is generally determined by the next day does not feel fatigue as the degree, 3 ~ 5 days per week training.
3.Exercise precautions
The following points should be noted when carrying out exercise prevention and treatment of osteoporosis.
① Emphasize the principle of tertiary prevention: for people with rapid bone loss, appropriate prevention and treatment countermeasures should be taken early. Pay attention to the active treatment of diseases related to osteoporosis, such as diabetes, rheumatoid arthritis and chronic nephritis. For elderly patients with osteoporosis, drug therapy to inhibit bone resorption and promote bone formation should be actively carried out.
②Adhere to the principle of individualization: that is, according to the individual bone volume change, the degree of loss, the degree of severity, the fracture situation and the various specific requests of the middle-aged and elderly people, choose the exercise prevention and exercise therapy programs and pay attention to the corresponding coordination with various means.
Bone loss and mild osteoporosis without fracture: muscle strength exercises, such as sitting and lying muscle strength exercises, aerobic exercises, weight training (weights should be close to the body, avoiding spinal flexion) and balance training can be carried out.
Moderate and severe osteoporosis: back extension exercises, muscle strength of abdominal muscles as well as upper and lower limb muscle strength exercises, balance training and aerobic exercises should be performed under the guidance of a therapist. In addition, 30 to 40 minutes of daily walking is beneficial to stimulate bone formation. The intensity of exercise needs to be increased when physical condition permits.
People with osteoporosis combined with vertebral, hip and wrist fractures: necessary rest should be performed under fixation in the acute stage, or activities of the unfixed limb should be performed under the guidance of a physician or rehabilitation technician.
③ Planning the phase of exercise: insisting on long-term planned and regular exercise has a better effect on delaying bone loss.
④Pay attention to the control of the amount of exercise: In the treatment or prevention according to the exercise prescription, it is required to gradually adapt to the intensity and amount of exercise, and pay attention to the principle of recovery from overload, but should not be forced. There should be no feeling of fatigue after exercise, otherwise it means that the exercise intensity is excessive.
⑤ Strengthen the regular physical examination to observe any adverse changes and timely evaluation of exercise effects.
⑥ pay attention to preparatory activities and finishing activities: adequate preparatory activities can make the body gradually adapt to the greater intensity of training to prepare and prevent the occurrence of sports injuries such as muscle strains. Pay attention to finishing and relaxation at the end, can effectively prevent adverse effects on the body due to the sudden cessation of exercise. Such as causing gravitational shock.