Loss of muscle mass and strength is universal across the aging population. A perhaps surprising amount of this loss is the result of lifestyle choice, however. We live in an age of comfort, in which people conduct lesser degrees of physical activity than was normally the case in past centuries. Compare the average modern first world individual with the average modern hunter-gatherer, and the hunter-gatherer is in better shape, better maintaining muscle function into later life. Given than people age at different rates, and people undertake different degrees of physical activity, one might expect to see variations in muscle mass and strength in later life, and indeed this is the case.
In today's open access paper, researchers examine the correlation between measures of strength and mortality in a population over 90 years of age. The more muscle, the lower the mortality risk. It is worth bearing in mind other studies that have shown programs of resistance exercise, which builds muscle and strength, to lower mortality risk in older individuals. A fair degree of the state of muscle in later life is under our control. Muscle is a metabolically active tissue, producing a comparatively poorly understood set of myokine signals that are generally beneficial to the operation of metabolism throughout the body. So having more muscle, and better quality muscle tissue, isn't just a matter of avoiding frailty, it is also beneficial in other ways.
Ageing is associated with a gradual loss of muscle strength, which in the end may have consequences for survival. Whether muscle strength and mortality risk associate in a gradual or threshold-specific manner remains unclear. This study investigates the prospective association of muscle strength with all-cause mortality in the oldest old. We included 1890 adults aged ≥ 90 years (61.6% women, mean age 91.0 ± 1.5 years) from 27 European countries and Israel participating in the Survey of Health, Ageing and Retirement in Europe (SHARE) study. Muscle strength was assessed using handgrip dynamometry. We determined the prospective association of muscle strength with mortality, controlling for age, sex, smoking, BMI, marital status, education, geographical region, and self-perceived health.
Over a mean follow-up of 4.2 ± 2.4 years, more than half of the participants died (n = 971, 51.4%). The mean handgrip strength was 20.4 ± 8.0 kg for all participants, with men (26.7 ± 7.5 kg) showing significantly higher strength than women (16.4 ± 5.4 kg). Using the median level of muscle strength as reference (18 kg), lower and higher levels were associated in a gradual and curvilinear fashion with higher and lower mortality risk, respectively. The 10th percentile of muscle strength (10 kg) showed a hazard ratio (HR) of 1.27. The 90th percentile (31 kg) showed an HR of 0.69. Stratified for sex, the median levels of muscle strength were 26 kg for men and 16 kg for women. The 10th percentile of muscle strength showed HRs of 1.33 at 15 kg for men and 1.19 at 10 kg for women. The 90th percentile of muscle strength showed HRs of 0.75 at 35 kg for men and 0.75 at 23 kg for women. Sensitivity analyses, which excluded individuals who died within the first 2 years of follow-up, confirmed the main findings.
Rather than a specific threshold, muscle strength is gradually and inversely associated with mortality risk in the oldest old. As muscle strength at all ages is highly adaptive to resistance training, these findings highlight the importance of improving muscle strength in both men and women among the oldest old.
View the full article at FightAging
