It is well established that diet and physical activity are the most important non-pharmacological measures to prevent diabetes, cardiovascular disease and age related musculoskeletal disorders, as well as to improve the quality of life in the aging society.
More specifically, skeletal muscle mass and strength are important factors in maintaining independence and quality of life in older individuals (Watanabe et al, 2015). Reductions in lean muscle mass is associated with a decrease in resting energy expenditure, overall decrease in fat oxidation as well as reductions in physical activity (Poehlman et al, 1995).
Furthermore, bone mineral density is related to muscle mass and strength in older adults which implicates sarcopenia in the development of osteopenia and its progression to osteoporosis (Thomas and Greig, 2017).
Sarcopenia
Sarcopenia is the age-related loss in skeletal muscle mass and strength and is associated with the risk of falls and fractures, physical disability, loss of independence, lifestyle related diseases and mortality (Rolland et al, 2008).
Evidence suggests that strength peaks in the third decade of life, remains unchanged or decreases slightly into the fifth decade, and then declines more rapidly at a rate of 12-15% per decade thereafter (Hurley, 2005); with reductions in strength most notable in the weight bearing lower limb muscles (Lamders et al, 2005). Muscle power (the ability to apply strength rapidly) appear to decline more rapidly with age and may in fact be more important than strength in prevention of falls (Caserotti et al, 2001).
The strength loss accompanying sarcopenia decreases the capacity to perform everyday tasks (figure 1.). For example, many individuals over the age of 55 have difficulty in walking 400m or carrying 11kg (Sheapard, 1997). By the age 80 years up to 57% of men and 70% of women are unable to do heavy housework (Sheapard, 1997). Therefore, it is apparent that a loss in muscle mass and consequently strength/power is a major contributing factor to a reduced quality of life with age and may decrease longevity.
Potential Causes
There are numerous potential causes for the onset of sarcopenia as we age. One potential cause is the decrease in a variety of circulating growth hormones (insulin-like growth factor-1, testosterone etc.) another cause may be that lack of muscle use has been shown to increase circulating levels of myostatin (Wehling et al, 2000). Myostatin is a protein that inhibits muscle growth and has been shown to be inversely related to muscle growth (Schulte et al, 2001).
Skeletal muscle is a highly plastic tissue and is influenced by the stress that is placed upon it. Consequently, there is a rapid response to unloading of the tissue; therefore, lack of physical activity, bed rest, immobilisation all result from significant reductions in skeletal muscle mass (Bamman et al, 1998). As a result, some studies have found that the older population, which is less physically active are at a higher risk of developing sarcopenia (Lee et al, 200).
Prevention
Resistance training is the single most effective strategy at combating sarcopenia by stimulating muscle growth and increasing strength. Resistance training can be defined as static or dynamic muscular contractions against external resistance of varying intensities.
Increases in strength and muscle mass after resistance training lead to improved performance in activities of daily life (Schlicht et al, 2001). Frontera et al (1988) reported that a group of older adults (60-72 years old) who performed 12 weeks of resistance training showed an 11% increase in muscle mass and an improvement in muscle strength.
Resistance training has been shown to be successful in improving cardiovascular health by reducing blood pressure (Shaw et al, 2010), improving blood lipid profiles by reducing LDL (bad) cholesterol and increasing HDL (good) cholesterol (Williams et al, 2011) and reducing the cardiovascular demands to physical activity (Kraemer et al, 2002).
Furthermore, resistance training has proved essential in improving and promoting physical performance, movement control, walking speed, functional independence, cognitive abilities and self-esteem (Hunter et al, 2004; Phillips, 2007; Westcott, 2012). Other less recognised benefits include a reduction in depression and improved sleep (Singh et al, 2005).
Additionally, although there is no evidence suggesting that resistance training can reverse major biological or behavioural outcomes of diseases such as cerebral palsy or Alzheimer’s disease, there is increasing evidence suggesting that the prevalence of these conditions are inversely related to muscle mass and strength (Hurley et al, 2011), further highlighting the importance of resistance training for mental health.
There is a direct link between poor physical function and poor nutrition with insufficient protein ingestion, vitamin D deficiencies, lack of anti-oxidant nutrients (berries, spinach, kale) and long chain polyunsaturated fatty acids (oily fish, coconut oil) (Robinson et al, 2015).
Limited nutrition and monotonous diets are common in aged population increasing the risk of poor nutrient ingestion. Therefore, interventions aimed at improving nutrition will have beneficial effects on delaying loss of muscle mass and physical function. High protein diets and protein supplementation are currently the most effective nutritional treatments for sarcopenia and muscle loss (Drescher et al, 2015).
The recommended daily intake of protein of 0.8g/kg/day may not be a sufficient amount to maintain muscle mass in older populations due to anabolic resistance (Landi et al, 2016). Anabolic resistance is a reduction in muscle protein synthesis observed after a dose of protein is administered and greatly contributes to decreases in muscle mass. As a result, older adults require increased levels of protein in order to maintain proper muscle functioning. Rates of muscle protein synthesis are regulated by mostly by responses to anabolic stimuli such as resistance training and protein ingestion (Landi et al, 2016). Consequently, older adults would benefit from increased levels of protein consumption from 1.2-1.5g/kg/day (i.e. a 70kg person would require 84g-105g of protein per day) and in the case of the elderly >2.0g/kg/day.
Practical Application
Resistance training in older adults significantly increases muscle mass, strength and power, reduces the difficulty of performing everyday tasks, increases energy expenditure and improves body composition.
Basic guidelines to induce muscle hypertrophy include using a load intensity of approximately 60-80% 1RM (1 repetition maximum, which is the load that can be lifted for only one repetition) which corresponds to between 8-15 repetitions, performed for 2-4 sets. Each muscle group should be exercised 2-3 days per week.
Interestingly, a study from Hakkinen et al (2001) showed that older women benefited more from a maximum of 2 days resistance training per week suggesting that women required longer rest duration between high intensity bouts of resistance training in order to maximise muscle adaptations.
Additionally, the inclusion of a low intensity (40% 1RM) high velocity muscular contractions are recommended on at least one day per week in order to develop muscular power.
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