body composition.
Role of exercise in preserving muscle mass with age
In contrast to changes in fat and bone, an increase in muscle mass is achievable to a significant degree only with progressive resistance training or generalised weight gain from extra energy and protein consumption. Accretion of lean tissue with exercise has a potential role in preventing diabetes,82 functional dependency, falls, and fractures, and is important in the treatment of chronic diseases and disabilities, which are accompanied by disuse, catabolism, and sarcopenia. For some diseases, such as type 2 diabetes mellitus, there are potential advantages to both minimising fat tissue and maximising muscle tissue since these compartments have opposite and likely independent effects on insulin resistance in older adults. Resistance exercise coupled with a leucine‐enriched essential amino acid supplement (when diet is inadequate) is recommended to treat sarcopenia.83 Muscle wasting or atrophy from any cause will exacerbate problems related to the extent and rate of the peripheral disposal of glucose into skeletal muscle, which is essential for maintaining euglycaemia in response to normal metabolism, meals, or other stressors. There is evidence from a variety of epidemiological and experimental studies that muscle weakness, decreased muscle mass, decreased activation of glycogen synthase, and alterations in numbers of type IIb skeletal muscle fibres are related to, and may precede, insulin resistance, glucose intolerance, and type 2 diabetes expression. Thus, the typical alterations in body composition with ageing (decreased muscle mass and increased visceral adiposity) are potentially independently related to the development of impaired glucose homeostasis in older adults.
Exercise to maintain or increase muscle mass
Appropriate progressive resistance training programmes of 3–6 months' duration can be shown to increase muscle strength by an average of 40–150%, depending on the subject's characteristics and intensity of the programme and to increase total body lean mass by 1–3 kg or muscle fibre area by 10–30%.84 Thus, even if some of the neural control of muscle and the absolute number of motor units remaining is not affected by exercise, the adaptation to muscle loading, even in very old age,85 causes neural, metabolic, and structural changes in muscle, which can compensate for the strength losses and, in some cases, the atrophy of ageing. Generally, strength gains after exercise far exceed, and are not directly correlated with, muscle size changes due to the importance of neural adaptation in this process.
A properly designed resistance training programme can counteract the age‐related changes in contractile function, atrophy, and morphology of ageing human skeletal muscle.86 Besides being safe for healthy older adults,87 a properly designed resistance exercise is relatively free of potential unwanted side effects caused by common medications prescribed in patients with multiple comorbidities.22,87 Both research and clinical experience indicate that resistance training is safe for healthy older adults,88 frail (physiologically vulnerable) older adults,89,90 and individuals with disease.22
Predictors of muscle hypertrophy after exercise
There is some controversy about whether there are significant gender differences in the functional or hypertrophic response to resistance training in the elderly. Some studies have found women to have smaller gains in muscle strength and power or hypertrophic response to training, whereas others have found no differences or even greater gains in women. It is likely that differences in training regimens (particularly related to intensity) and measurement techniques used to assess muscle mass, cross‐sectional area or volume may explain some of these discrepant results. Malnutrition, impaired protein synthesis rates, inflammatory cytokines, and depression are other factors that have been identified as detrimental to robust anabolic and functional adaptations to resistance training in some studies, and the role of genetic and epigenetic influences is still under investigation.91
Muscle power training
Preserving muscle power output is critical to counteract the age‐related decline of functional capacity and also the earlier and more precipitous decline in muscle power and its associated disability relative to muscle strength in older men and (particularly) women. Muscle power output and rate of force development are strongly associated with the capacity to perform daily living activities in elderly populations.92‐94 Indeed, strong associations between functional capacity test performance and muscle power output or rate of force development have been previously shown in the healthy elderly.92‐94 More recently, it has been found that muscle power and explosiveness are also associated with functional capacity and incidence of falls in the oldest old populations, including the frail, institutionalised oldest old.93‐95 Muscle power training should be prescribed in both healthy and frail elderly individuals, in combination with traditional slow concentric velocity resistance training, because this type of training optimises functional ability gains, reduces the incidence of falls, improves muscle strength and power output, and stimulates muscle hypertrophy.6
Optimal training regimens for maximising muscle power should be performed with the concentric phase as fast as possible, followed by a controlled slower eccentric phase, and emphasised in lower limbs.96,97 The sets using explosive muscle actions can be performed alone17,98 or combined with traditional resistance training during the same session, but always avoiding concentric failure.96,99,100 Power is maximised at 30–45% loads for the upper extremity and 60–80% of peak force capacity (one repetition maximum or 1 RM) for the lower extremity extensors.53,101 In a dose‐response study,101 it was shown that peak muscle power was improved similarly using light (20%), moderate (50%), or heavy (80%) resistances, whereas there was a dose‐response relationship between training intensity and muscle strength and endurance changes favouring high‐intensity training.102 Therefore, using heavy loads during explosive resistance training may be the most effective strategy to achieve simultaneous improvements in muscle strength, power, and endurance in older adults. In addition, power training at low loads (during which velocity is much faster) poses a risk of meniscus or tendon injuries if undiagnosed degenerative changes are present, as is common in older adults.103,104
Several studies have used standard free weights and weight machines for power training,17,96,105 but some studies used pneumatic resistance machines designed specifically for this type of resistance training,106,107 resulting in similar neuromuscular and functional improvements.108 As it is not possible to overcome resistance with momentum on such machines (as can be done by ‘swinging’ a free weight), they offer a theoretical and practical advantage. In the absence of such machines for power training, plyometric training (e.g., jumping up onto platforms/boxes) has traditionally been used in children and athletes for this purpose. However, arthritis and balance impairment preclude plyometrics in many frailer adults most in need of such muscle power improvements. As an alternative, the use of body weight as resistance (e.g., rising quickly from a chair) may be substituted as an initial strategy. It could start with slower execution and another person’s assistance but progress until the person can perform it alone and as fast as possible. This strategy may be easily performed in hospital rooms, at home, or in aged care residences. However, once body weight is no longer a sufficient overload of the capacity of lower extremity muscles, additional resistance provided by machines or free weights is needed to ensure progression.
Promotion of psychological well‐being
Psychological well‐being is vital to optimal ageing and is dependent on a host of factors, including genetic traits, social support systems, personality types, and the presence of positive and negative psychological constructs such as happiness, optimism, morale, depression, anxiety, self‐esteem, self‐efficacy, and vigour. Participating in physical activity has been shown
