Abstract
Age-related muscle wasting (sarcopenia) is accompanied by a loss of strength which can compromise the functional abilities of the elderly. Muscle proteins are in a dynamic equilibrium between their respective rates of synthesis and breakdown. It has been suggested that age-related sarcopenia is due to: i) elevated basal-fasted rates of muscle protein breakdown, ii) a reduction in basal muscle protein synthesis (MPS), or iii) a combination of the two factors. However, basal rates of muscle protein synthesis and breakdown are unchanged with advancing healthy age. Instead, it appears that the muscles of the elderly are resistant to normally robust anabolic stimuli such as amino acids and resistance exercise. Ageing muscle is less sensitive to lower doses of amino acids than the young and may require higher quantities of protein to acutely stimulate equivalent muscle protein synthesis above rest and accrue muscle proteins. With regard to dietary protein recommendations, emerging evidence suggests that the elderly may need to distribute protein intake evenly throughout the day, so as to promote an optimal per meal stimulation of MPS. The branched-chain amino acid leucine is thought to play a central role in mediating mRNA translation for MPS, and the elderly should ensure sufficient leucine is provided with dietary protein intake. With regards to physical activity, lower, than previously realized, intensity high-volume resistance exercise can stimulate a robust muscle protein synthetic response similar to traditional high-intensity low volume training, which may be beneficial for older adults. Resistance exercise combined with amino acid ingestion elicits the greatest anabolic response and may assist elderly in producing a 'youthful' muscle protein synthetic response provided sufficient protein is ingested following exercise.
Highlights
Demographics indicate that the world’s population aged 60 years and over will more than triple within 50 years from 600 million in the year 2000, to more than 2 billion by 2050 [1]
Studies into the role of protein turnover in agerelated sarcopenia reported that muscle wasting in the elderly was due to a decline in basal rates of muscle protein synthesis (MPS) [22,23,24], elevated basal rates of MPB [25], or a combination of the two processes resulting in a negative net protein balance
We have shown previously in young adults that 5 g and 10 g of egg protein ingestion after resistance exercise is sufficient to acutely increase MPS above basal, a response that becomes saturated with 20 g of egg protein
Summary
Demographics indicate that the world’s population aged 60 years and over will more than triple within 50 years from 600 million in the year 2000, to more than 2 billion by 2050 [1]. Studies into the role of protein turnover in agerelated sarcopenia reported that muscle wasting in the elderly was due to a decline in basal rates of MPS [22,23,24], elevated basal rates of MPB [25], or a combination of the two processes resulting in a negative net protein balance. Evidence suggested that age-related sarcopenia was the result of slower rates of basal, postabsorptive myofibrillar MPS and a more negative net protein balance in the elderly (aged >60), as compared with young adults [22,23,24]. A general inconsistency of findings by others to demonstrate reduced rates of MPS or markedly elevated MPB in healthy older adults [27,28,29], have led to the general agreement that basal skeletal muscle net protein balance is not compromised with ageing [27]. TNF-a, which is one of the main inducers of the acute-phase response [39], plays an MPS in young MPB in young and elderly MPS in elderly
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