Abstract
Declines in strength and muscle function with age—sarcopenia—contribute to a variety of negative outcomes including an increased risk of: falls, fractures, hospitalization, and reduced mobility in older persons. Population-based estimates of the loss of muscle after age 60 show a loss of ~1% per year while strength loss is more rapid at ~3% per year. These rates are not, however, linear as periodic bouts of reduced physical activity and muscle disuse transiently accelerate loss of muscle and declines in muscle strength and power. Episodic complete muscle disuse can be due to sickness-related bed rest or local muscle disuse as a result of limb immobilization/surgery. Alternatively, relative muscle disuse occurs during inactivity due to illness and the associated convalescence resulting in marked reductions in daily steps, often referred to as step reduction (SR). While it is a “milder” form of disuse, it can have a similar adverse impact on skeletal muscle health. The physiological consequences of even short-term inactivity, modeled by SR, show losses in muscle mass and strength, as well as impaired insulin sensitivity and an increase in systemic inflammation. Though seemingly benign in comparison to bed rest, periodic inactivity likely occurs, we posit, more frequently with advancing age due to illness, declining mental health and declining mobility. Given that recovery from inactivity in older adults is slow or possibly incomplete we hypothesize that accumulated periods of inactivity contribute to sarcopenia. Periodic activity, even in small quantities, and protein supplementation may serve as effective strategies to offset the loss of muscle mass with aging, specifically during periods of inactivity. The aim of this review is to examine the recent literature encompassing SR, as a model of inactivity, and to explore the capacity of nutrition and exercise interventions to mitigate adverse physiological changes as a result of SR.
Highlights
PHYSICAL ACTIVITY AND AGINGIn Canada, ∼85% of individuals are not meeting physical activity guidelines [1]. This highlights the potential for improvement that could be achieved given the potential for increased physical activity to reduce risk for a number of diseases and for all-cause mortality [2, 3]
Specialty section: This article was submitted to Sport and Exercise Nutrition, a section of the journal Frontiers in Nutrition
High quality protein in large quantities has a potent anabolic effect on older skeletal muscle, we recently aimed to examine the effects of a high protein diet to mitigate skeletal muscle loss and reductions in muscle protein synthesis (MPS) in healthy older adults during step reduction (SR)
Summary
In Canada, ∼85% of individuals are not meeting physical activity guidelines [1]. This highlights the potential for improvement that could be achieved given the potential for increased physical activity to reduce risk for a number of diseases and for all-cause mortality [2, 3]. Acute bouts of inactivity that result in unloading of muscles manifest due to a variety of circumstances (illness, injury, poor weather conditions) and are distinctly different from habitual sedentary behavior. Though these acute disruptions in activity may be seemingly benign, we hypothesize that accumulated bouts of marked inactivity superimposed on a physically inactive population is a major risk for negative physiological health outcomes and may accelerate sarcopenia and the development of chronic cardiometabolic conditions associated with aging
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