The effects of growing older are evident to everyone; reduced ability to recover, reduced mobility, diminished elasticity of the skin and so on. However aging or senescence also change the way in which protein intake from the diet stimulates muscle protein synthesis in response to exercise and relaxation states. If you are an individual aged in your forties or, it is important that you are conscious of these effects, as it will assist in optimising responses to exercise.
SENESCENCE AND SARCOPENIA
Sarcopenia represents age related loss of skeletal muscle mass, which coercively results in diminished tensile strength and cardiovascular endurance and therefore a reduced overall physical capacity. It occurs due to an imbalance between the synthesis and breakdown of skeletal muscle proteins, and accounts for a reduced muscle mass of up to 50% of skeletal muscle tissue, between the ages of 20 and 80 years of age. After reaching 50 years of age, the average individual is expected to lose approximately 1–2% of muscle mass per year, whilst tensile strength diminishes at a faster rate. ANABOLIC
RESISTANCE IN OLDER ADULTS
The response of muscle protein synthesis (MPS) to physical stimuli like resistance training and consuming protein, is reduced in older adults compared to younger individuals. This inability of older adults’ muscles respond to protein ingestion and resistance exercise has been termed ‘anabolic resistance’.
LEUCINE THRESHOLD IN OLDER ADULTS
One of the critical factors in stimulating muscle protein synthesis is meeting and passing a threshold for leucine. Research studies have shown that amino acid and protein formulas require higher leucine contents in order to stimulate muscle protein synthesis in older adults compared to their younger counterparts, and in studies comparing the cohort groups of the same age, diets containing supplemental leucine content were shown to stimulate muscle protein synthesis more than diets with no leucine supplementation. SOURCE OF PROTEIN AND OLDER ADULTS Comparisons of the effects of different protein supplements on cohorts of older adults have shown that whey protein provides the greatest stimulus to muscle protein stimulus compared to other dairy protein sources. Incidentally whey contains greater leucine content than other dairy protein sources. Moreover high doses of greater than 30g whey protein provided greater stimulation of muscle protein synthesis than does of 10g or 20g in older adults indicating a higher threshold point for optimisation than in younger adults.
POST-WORKOUT PROTEIN INTAKE IN OLDER ADULTS
In research of optimal protein intakes following exercise in cohorts of older males, supplementation of 20g and 40g of whey protein showed stimulation of muscle protein synthesis, whereas intakes of 0g and 10g of protein in rested states showed no activation of muscle protein synthesis. Following resistance training, activation of muscle protein synthesis was shown with supplementation of 0,10, 20 and 40g whey protein. However supplementation of 20g and 40g of whey protein showed greater activation of muscle protein synthesis than supplementation of 0g and 10g whey protein, with greatest activation of muscle protein synthesis following supplementation 40g whey protein. In younger adults, research has shown no greater activation of muscle protein synthesis following 20g protein supplementation following training compared to 40g protein following training, meaning greater volumes of protein are required after exercise as we age.
The research evidence regarding ‘anabolic resistance’ in older adults is compelling. The skeletal muscle tissue of older adults is more resistant to typical anabolic stimuli like resistance training and protein/amino acids. The muscles of aging individuals are not as responsive to lower intakes of protein and amino acids, and it is necessary for older adults to consume higher volumes, in order to stimulate muscle protein synthesis to the same degree as younger counterparts. Practically speaking, it is critical that older adults consume sufficient protein at each meal, (a minimum of 20g) in order to optimise muscle protein synthesis. Moreover the type of protein is more important in older adults. Research has highlighted the benefits of high volumes of the branched chain amino acid leucine and the benefits of whey protein, compared to other sources. Resistance training in combination with the consumption of protein and/or amino acids results in the greatest anabolic response in older adults and is the best known method for older adults to produce a similar muscle protein synthesis response to younger individuals, as long as sufficient protein is consumed after training.