Declines in Limb Muscle Mass Correlate with Higher Mortality in Late Life
Given that resistance training is shown to reduce mortality in older individuals, it makes sense that we would see the opposite effect when looking at low muscle mass in limbs. Skeletal muscle isn't an inert tissue, being quite involved in insulin metabolism, for example, and exercise has all sorts of interesting effects on the operation of metabolism, such as up-regulation of beneficial cellular stress response mechanisms. Aging is associated with a progressive loss of muscle mass and strength, with the loss of stem cell activity being a leading cause. This ultimately results in frailty and the condition of weakness known as sarcopenia. In our modern societies of sedentary convenience, this loss is much faster that it would otherwise be if people were more active, and hence the point that resistance training improves matters from the present baseline. That is only the case because most older people do not undertake any sort of effort to maintain muscle mass and strength.
Evaluating body composition, especially appendicular muscle mass, can be an effective strategy for predicting longevity in people over 65 years of age, according to a new study. The appendicular muscles are the muscles that move the appendages or extremities - the arms and legs. They also play a key role in stabilizing the shoulders and hips. The researchers studied a group of 839 men and women over the age of 65 for approximately four years. They observed that all-cause mortality risk increased nearly 63-fold during the follow-up period in women with low appendicular muscle mass and 11.4-fold in men.
"We evaluated the body composition of this group, focusing on appendicular muscle mass, subcutaneous fat, and visceral fat. We then sought to determine which of these factors could predict mortality in the ensuing years. We concluded that the key factor was the amount of appendicular lean mass." Body composition was determined by dual energy X-ray absorptiometry (DXA), also known as bone density scanning, using a densitometer. The study sample comprised 323 men (39%) and 516 women (61%). The frequency of low muscle mass was approximately 20% for both men and women.
Generally, subjects who died were older, exercised less, and suffered more from diabetes and cardiovascular problems than those who remained alive. In the case of the women who died, they also had decreased BMI. The men who died were more likely to suffer falls. All these variables were fed into the statistical model and adjusted for the end-result to show which body composition factor correlated best with mortality risk. Only low muscle mass was found to be significant in the women, considering the adjustment variables, while visceral fat was also significant among the men.
Menopause-related hormone changes may help explain the difference between men and women. "The rapid and significant transition from a protective estrogenic environment to a deleterious hypoestrogenic environment, which is particularly adverse for the cardiovascular system, may make the protective metabolic role of skeletal muscles, including the production of anti-inflammatory cytokines, more important in the postmenopause period. This hormone change is far less abrupt in men."
In addition to their obvious importance in posture, balance and movement, the skeletal muscles have other functions that are essential to the body. They help regulate blood sugar by consuming energy during contraction and maintain the body temperature by trembling when cold. They also produce messenger hormones, such as myokinase, that assist communication with different organs and influence inflammatory responses. The good news is that sarcopenia is preventable and can even be reversed by physical exercise, especially muscle toning. Attention to protein ingestion is also recommended.