Muscle contracts only when stimulated by nerves. If nerve supply to muscle get severed, muscle gradually weakens or atrophies.
The old may limp because of calcium deficiency or deficiency of vitamin D3 which is responsible for calcium absorption.
Injury to limb or girdle bones also hamper locomotion. But, these apart, some muscular and skeletal disorders are hereditary e.g. Myaesthenia gravis and Muscular dystrophy. Arthritis and Rheumatoid arthritis may or may not be hereditary. Osteoporosis and Gout are due to nutritional deficiency and metabolic errors.
Myaesthenia gravis is because of a gene on X chromosome and so is hereditary. The muscles slowly waste away and the patient gradually becomes immobile and in the last stages even the jaw muscles do not work and patient is unable to eat.
Muscular dystrophy is an autosomal dominant disorder. In this hereditary disorder, muscles waste away and person becomes immobile.
Arthritis and Rheumatoid arthritis are disorders of bones especially joints. There is constant joint pain in Rheumatoid arthritis which is a crippling disease. Hands and feet become crooked due to inflammation in the joints.
Osteoporosis is the softening of bones due to calcium deficiency. Calcium absorption is dependent on availability of Vitamin D. So it is important to expose oneself to the sun every day for atleast half an hour. Sunlight helps to generate Vitamin D. Women, post menopause are prone to osteoporosis. Estrogen, the female hormone mobilises calcium and sends it to bones. In the absence of estrogen, bones tend to crack and break.
Gout results in painful inflammation of joints due to elevated level of uric acid in blood. Uric acid is a product of protein metabolism. Gout can be cured.