The Impact of Step Reduction on Muscle Health in Aging: Protein and Exercise as Countermeasures

[madman]

REVIEW ARTICLE
Front. Nutr., 24 May 2019 | The Impact of Step Reduction on Muscle Health in Aging: Protein and Exercise as Countermeasures


The Impact of Step Reduction on Muscle Health in Aging: Protein and Exercise as Countermeasures
Sara Y. Oikawa, Tanya M. Holloway, and Stuart M. Phillips*

• Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, ON, Canada

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 the 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.




Conclusion

Though it would be considered a significantly less catabolic stimulus than bed rest, SR as a model of reduced activity results in marked negative alterations in skeletal muscle health in younger and older adults. Periods of SR may occur at increased frequencies in comparison to complete unloading and with, we speculate, underappreciated consequences. In younger persons such periods may not be as deleterious as in older persons since, even given the small number of observations, it appears that older persons have difficulty fully recovering from SR or disuse. We propose that the periodic effects of muscle disuse and SR and the cumulative negative consequences that should be considered in addressing the longer-term health of aging individuals. These periods accelerate muscle loss and induce metabolic dysfunction which for older persons would have deleterious consequences. Resistance exercise, even low load and sporadically performed, may serve as an effective strategy to offset disuse-induced losses in skeletal muscle with SR. Importantly, resistive exercise combined with nutritional stimuli (high-quality protein, creatine, and n-3 fatty acids, energy balance) may aid in attenuating the decline in LBM with disuse and aid in the rehabilitation of muscle mass. Given, that nutritional modification or RT is not always feasible during disuse, future research should aim to examine how to improve the recovery period from SR using exercise, rehabilitation, or supplementation to improve the physiological decline with disuse.

 

[madman]

Figure 1. Factors influencing the progression of sarcopenia. Representations of normal sarcopenic muscle loss and accelerated muscle loss as shown by a punctuated decline.

 

[madman]

Figure 2. Physical inactivity models used in human skeletal muscle metabolism. Typical sarcopenic muscle loss based on population estimates (24). Sedentary behavior as categorized by Walhin et al. as < 4000 steps per day induced significant insulin resistance in healthy young adults (25). Interestingly, during one week of bed rest, participants walked for ~22 minutes per day (~2000 steps) in an effort to offset bed rest induced muscle atrophy however exercise was not able to mediate this effect and muscle loss was similar to controls (26). Step reduction, or abruptly reducing habitual daily steps to 750-1500 steps per day results in leg lean mass loss over two weeks in healthy young and older adults (13, 14, 27). Bed rest induces rapid muscle atrophy in healthy older adults (9) however the rate of muscle loss per day as a result of space flight or exposure to microgravity are staggering (28).

 

[madman]

Figure 3. Comparison of disuse models used to study inactivity highlighting the whole body systemic nature of bed rest and step reduction compared to limb immobilization. Data regarding the prevalence of events with induced step reduction is currently unknown.

 

[madman]

Figure 4. Muscle protein synthesis (MPS) and muscle protein breakdown (MPB) in responses to grams of protein per meal. Solid lines indicate MPS, dashed lines indicate MPB. Blue hashed areas indicate positive protein balance while the red dotted areas indicate negative protein balance. Blue hashed areas and red dotted areas equate to the same area under the curve indicating net protein balance.

 

[Nelson Vergel]

Simplified by AI:

Title: The Impact of Reduced Physical Activity on Muscle Health in Older Adults

Abstract:

As people age, they experience a decline in strength and muscle function, which is called sarcopenia. This can lead to negative outcomes such as an increased risk of falls, fractures, and reduced mobility. Studies show that after age 60, people lose about 1% of their muscle mass each year and 3% of their strength each year. However, when people have periods of reduced physical activity, like when they're sick or recovering from an illness, the loss of muscle can be even faster. This can happen frequently as people age due to illness, declining mental health, and mobility issues. Even short periods of inactivity, called step reduction, can have negative effects on muscle mass, strength, insulin sensitivity, and inflammation. We believe that accumulated periods of inactivity contribute to sarcopenia.

The good news is that even small amounts of activity and protein supplements can help offset the loss of muscle mass with aging, especially during periods of inactivity. The aim of this review is to examine the recent literature on step reduction and explore how nutrition and exercise interventions can help mitigate the negative effects of reduced physical activity on muscle health.

In summary, as people get older, they experience a decline in strength and muscle function, which can lead to negative health outcomes. Even short periods of inactivity can make this decline worse. However, exercise and protein supplements can help offset these negative effects and improve muscle health.