Review articleExercise prescription for the older population: The interactions between physical activity, sedentary time, and adequate nutrition in maintaining musculoskeletal health
Introduction
Benefits of physical activity (PA) for older adults, particularly in the forms of resistance (e.g., muscular contraction using free-weights) and endurance (e.g., running or cycling) types of exercise are widely recognised. Regular PA has been shown to improve physical function and quality of life [1], [2], prevent sarcopenia, frailty and decrease the risk for cognitive decline [3], [4], [5], reduce the risks for obesity, coronary heart disease, and type 2 diabetes [6] and is associated with lower rates of all-cause mortality and diagnosis of new diseases [7].
PA guidelines recommend that older adults engage in a minimum of 150 min per week of moderate-to-vigorous intensity PA (MVPA) accumulated in bouts of at least 10 min, in addition to some resistance and flexibility exercises at least two days per week to maintain or improve strength and balance [8], [9], [10], [11]. MVPA is typically defined as any form of PA with a metabolic equivalent (MET) of ≥3 METs. Studies that have objectively measured MVPA in community-dwelling older adults indicate that a very small percentage (<5%) of this population meet the current guidelines [12], [13], [14], [15], [16], suggesting that these recommendations may not be realistic or attainable for the majority of older adults. For an in-depth overview of accelerometer-derived physical activity levels in older adults, interested readers are referred to a recent systematic review conducted by Sun and colleagues [16].
In addition to low levels of engagement in PA, sedentary behaviour is highly prevalent in older adults, with objective measures indicating that older adults may spend up to 85% of their waking hours being sedentary [12], [13], [17], [18]. Although emerging cross-sectional evidence suggests that increased time spent sedentary is a risk factor for development of chronic diseases, skeletal muscle loss (i.e., sarcopenia), functional disability, and premature mortality independent of physical activity [19], [20], [21], [22], the lack of evidence identifying the specific amount of time spent sedentary that increases one’s risks for diseases and functional disability has resulted in current recommendations for sedentary time being non-specific (i.e., keep sedentary time to a minimum) [9]. It has been argued that it may be easier to intervene to decrease sedentary time within older adults than increase PA to recommended levels, and emerging cross-sectional and experimental evidence highlights the beneficial effect that breaking up prolonged sedentary time can exert on both physical function and metabolic health [23], [24].
Recent evidence suggests the presence of ‘anabolic resistance’ in older adults, which has been proposed as an important underlying mechanism in the progression of sarcopenia [25], [26]. ‘Anabolic resistance’ refers to the dysregulation of the muscle protein synthetic response to anabolic stimuli (i.e., exercise and/or protein/amino acid-based nutrition). This research suggests a critical interaction between ‘sufficient’ levels of exercise and ‘adequate’ nutrition that promotes optimal physical function and metabolic health in older adults. However, current PA recommendations do not take into account the important role that nutrition plays in ensuring older adults can maximise the benefits from the exercise in which they engage.
The aims of this narrative review are to: (i) briefly summarise the evidence used to inform current public health recommendations for PA and sedentary time in older adults; (ii) examine what is currently known about the beneficial effects of PA and reduced sedentary time on musculoskeletal health in older adults; (iii) discuss the presence of ‘anabolic resistance’ in older adults, highlighting the interactions between PA and nutritional intake in optimising functional and metabolic responses in older adults; and (iv) re-examine the current recommendations for PA and sedentary time in light of the evidence presented.
Section snippets
Methods
A narrative review was conducted, drawing upon the international English-language literature published up to April 2016, using the Ovid MEDLINE (1946 to April 2016) and EMBASE (1974 to 10th, April 2016) databases. Search terms were: “human/humans,” “old,” “elder,” “physical activity,” “exercise,” “physical activity recommendations,” “physical activity guidelines,” “physical inactivity,” “sedentary behaviour,” “sedentary time,” “musculoskeletal,” “health,” “protein synthesis,” “muscle protein
Evidence informing current guidelines on physical activity and sedentary behaviour
There is consistently strong evidence indicating a positive association between increased PA and reduced risks for all-cause mortality, cardiovascular disease (CVD), type 2 diabetes, metabolic syndrome, and falls [8], [9]. The cross-sectional evidence linking increased sedentary time with elevated risk for all-cause mortality, CVD and metabolic diseases is relatively recent [19], [20], [21] and not without controversy [27]. Although the health benefits of regular PA are well documented, the
Physical activity, sedentary time, and musculoskeletal health
Evidence generated from experimental studies at the whole-body and cellular level indicates that regular participation in MVPA is fundamental to the preservation of skeletal muscle mass, strength, and physical function with advancing age [28], [29]. Though some loss of muscle mass and strength (i.e., sarcopenia) in later life may be inevitable, regular PA provides an effective means of slowing the progression of this debilitating condition [28]. The skeletal muscle adaptive response to regular
Anabolic resistance in older adults
Experimental interventions employing muscle disuse (e.g., bed rest and limb immobilisation) as a model of physical inactivity provide direct physiological evidence that brief and protracted unloading of skeletal muscle results in a loss of muscle mass, strength and physical function in older adults [34], [35]. Importantly, the increasing frequency of brief bouts of muscle disuse often experienced with advancing age (e.g., due to being hospitalised, injured or confined to the home due to adverse
Conclusion
The benefits of PA in optimising musculoskeletal function and metabolic health are well established, but the minimum amount of PA needed for older adults remains poorly defined. The coupling of PA (i.e., resistance-type exercise) and adequate nutrition (i.e., sufficient intake of essential amino acids/protein sources) is critical for preserving muscle anabolic sensitivity and thus maintaining skeletal muscle mass and metabolic health with advancing age [48]. As such, we strongly recommend that
Conflict of interest
None declared.
Contributors
Brandon J. Shad and Janice L. Thompson designed and drafted the manuscript.
Gareth Wallis and Luc J.C. van Loon conducted critical revisions of the manuscript.
Final approval of the manuscript was given by all authors.
Funding
Brandon J. Shad is funded by a University of Birmingham Exercise as Medicine PhD studentship.
Provenance and peer review
This article has undergone peer review.
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