The age-related loss in muscle mass, known as sarcopenia, can lead to significant debilitation in older adults. Biological factors that contribute to this loss in muscle mass as a person grows older include hormones, protein levels, motor units, muscle fiber types, and satellite cells.
Testosterone is a primary hormone that increases lean muscle mass in men. For women, growth hormone and IGF-1 are two primary hormones that maintain muscle mass. However, with age, the levels of these hormones tend to gradually decline, promoting the degeneration of muscle. Protein balance also affects muscle mass. Protein balance is the relationship between protein synthesis and protein degradation. Hypertrophy, which is the growth of muscle, happens due to an increase in protein synthesis and a decrease in protein degradation. Atrophy, which is the loss of muscle, is just the opposite. Many studies have been done to explore how protein synthesis can be increased to combat sarcopenia in elderly people. It is thought that anabolic resistance, which is the inability to respond to stimuli that increases protein synthesis, decreases in older adults and consequently leads to sarcopenia.
Three methods to treat sarcopenia have been studied: resistance exercise, protein intake, and anabolic steroids. Resistance exercise stimulates protein synthesis in both younger and older adults. However, younger adults experience a greater increase than older adults due to anabolic resistance. Thus, an older adult cannot be given the same exercise program as a younger adult. Additionally, older adults may need to engage in other types of strategies to effectively increase protein synthesis.
Protein synthesis has been shown to occur after acute resistance exercise. Researchers have studied the long-term effects of resistance training and have found that muscle size increases in older adults. In this study, elderly men engaged in resistance training for the legs for 12 weeks. The results of the study showed that these participants experienced a significant increase in quadriceps muscle after resistance training. Satellite cells, which help rebuild muscle, also showed an increase in these older adults. These participants also showed an increase in strength.
Studies have also explored the effects of protein ingestion on protein synthesis in older adults. The current recommended daily amount for adults 19 years of age and older is 0.8 g/kg per day. However, research has shown that this may not be enough for older adults who are sarcopenic. The amount of protein intake per meal matters when it comes to maintaining or building muscle mass. Research has shown that one must eat an adequate amount of protein for every meal in order to reach maximal protein synthesis. 25 to 30 grams of protein is suggested as the optimal amount of protein per meal. Any amount of protein that is greater than 30 grams will not be absorbed by the body. Moreover, an over-consumption of protein will not increase the rate of protein synthesis and may negatively affect the rate of glomerular filtration.
Older adults who are cared for by nursing home or assisted living facility staff must be given the proper amount of protein per meal and be encouraged to engage in the proper forms of resistance exercise.