US Pharm. 2010;35(9):24-30.
Aging causes muscle mass and muscle strength to decrease.1 By age 75 years, approximately 50% of an individual's total muscle mass has vanished.2 This age-related reduction in skeletal muscle mass is referred to as sarcopenia.3 But the process by which skeletal muscle mass progressively decreases, and thus lean body mass as well, begins occurring many years earlier--at about age 35 (TABLE 1).2,4
The cumulative loss of muscle mass results in decreased strength and exercise tolerance, weakness and fatigue, and a reduced ability to perform activities of daily living.4 Furthermore, a decrease in strength is a risk factor for poor balance, slowed gait, and falls.4 While most seniors retain adequate muscle mass and strength to perform all necessary tasks, individuals with the greatest loss in lean body mass are considered among the most vulnerable to falls and injuries.1,4 Ultimately, sarcopenia can have a profound impact on functional abilities of seniors in the oldest age brackets.4
Beyond the loss of strength, sarcopenia may alter the resting metabolic rate; irregularities in thermoregulation and the heat and cold intolerance seen in aging appear related to this occurrence.4 Additionally, the increasing insulin resistance and glucose intolerance seen in middle-aged and older-age populations is partially blamed on the gradual replacement of lean body tissue by adipose (and fibrous) tissue.4
Avoiding Prolonged Bed Rest
All patients are prone to muscle loss from prolonged bed rest.5 However, prolonged bed rest in the elderly can result in rapid acceleration of muscle loss and decrease in strength (deconditioning); additionally, stiffness of muscles, ligaments, and tendons, even to the extent of a resultant contracture, may occur.1,2,5 So significant can the muscle loss be in bedridden seniors that while complete bed rest causes young adults to lose about 1% of muscle mass per day, the elderly may lose up to 5% per day secondary to age-related decreases in growth hormone.5 In these individuals, muscle mass loss is greatest in the antigravity muscles (those used to sit up, stand up, and pull up) and can require up to 2 weeks of reconditioning to return to baseline function for each day of absolute bed rest.2 Patients should sit up in bed, transfer to a chair, stand, and exercise when safe to do so depending on their medical condition or surgical procedure.5 Patients need to be educated about the fact that avoiding sarcopenia is essential to recovery.5 Patients should be advised to avoid extended bed rest and immobilization when possible to prevent muscle weakness and joint stiffness.1
Growth Hormone Levels in Sarcopenia
Growth hormone (GH) levels decrease with aging; this decrease is probably one of many factors that contribute to sarcopenia.2 The age-related decrease in estrogen and testosterone may also reduce GH secretion.2 A number of the signs and symptoms of GH deficiency (e.g., decreased muscle mass, weakness, fatigue) are comparable to those that occur with normal aging.2 While increased muscle mass and decreased fat mass appear to occur with GH replacement therapy, muscle strength increases only to a small degree, if at all, unless GH is accompanied by weight training or is given with testosterone replacement therapy in hypogonadal men.2 GH supplementation should be used only as replacement therapy for those patients with a documented deficiency or for patients with muscle atrophy due to AIDS.2
Adverse effects associated with the supplementation of GH include arthralgias, carpal tunnel syndrome, fluid retention, glucose intolerance, gynecomastia, headaches, and lethargy.2 While long-term effects are unclear, elevated levels of GH and insulin-like growth factor I (IGF-I) in middle-aged individuals are associated with higher mortality rates than in those with lower levels of GH and IGF-I.2 While beyond the scope of this article, a broader discussion of the use and administration of GH supplementation, contraindications, IGF-I, and alternatives to GH may be found in Section 8, chapter 66 in Refe