Ingestion of sufficient dietary protein is a fundamental prerequisite for muscle protein synthesis and maintenance of muscle mass and function. The elderly are often at increased risk for protein-energy malnutrition, sarcopenia and a diminished quality of life. This study sought to compare changes in muscle protein synthesis and anabolic efficiency in response to a single moderate (113 g; 220 kcal; 30 g protein) or large serving (340 g; 660 kcal; 90 g protein) of 90% lean beef. Venous blood and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion (0.08 μmol/kg/min) of L-[ring-13C6] phenylalanine in healthy young (n=17; 34±3yrs) and elderly (n=17; 68±2yrs) individuals. Mixed muscle fractional synthesis rate (FSR) was calculated during a 3 h post-absorptive period and for 5 h following meal ingestion. Data were analysed using a two-way repeated measures ANOVA with Tukey's pair-wise comparisons. A 113 g serving of lean beef increased muscle protein synthesis by approximately 50% in both young and older volunteers. Despite a 3-fold increase in protein and energy content, there was no further increase in protein synthesis following ingestion of 340 g of lean beef in either age group. Ingestion of more than 30 g of protein in a single meal does not further enhance the stimulation of muscle protein synthesis in young and elderly.

In healthy older adults, 10 days of bed rest results in a substantial loss of lower extremity strength, power, and aerobic capacity, and a reduction in physical activity, but has no effect on physical performance. Identification of interventions to maintain muscle function during hospitalization or periods of bed rest in older adults should be a high priority.

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Background: Sarcopenia is a debilitating condition afflicting the elderly that may be facilitated by insufficient or ineffectual intake of dietary protein. We previously showed that free-form essential amino acids acutely stimulate muscle protein synthesis in both the young and the elderly. However, the ability of an actual protein-rich food to stimulate anabolism in the young and the elderly has not been explored. Objective: We aimed to characterize changes in plasma amino acid concentrations and to quantify muscle protein synthesis in healthy young (41 Ȁ 8 y old; n ҃ 10) and elderly (70 Ȁ 5 y old; n ҃ 10) persons after ingestion of a 113-g (4-oz) serving of lean beef. Design: Venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed (2.0 mol/kg) constant infusion (0.08 mol⅐kg Ҁ1 ⅐min Ҁ1 ) of L-[ring-13 C 6 ] phenylalanine. Plasma amino acid concentrations were measured and a mixedmuscle fractional synthesis rate (FSR) was calculated during the premeal period and for 5 h after beef ingestion. Results: Mixed-muscle FSR increased by Ȃ51% in both the elderly (mean Ȁ SE measurements: 0.072 Ȁ 0.004%/h and 0.108 Ȁ 0.006%/h before and after the meal, respectively) and the young (0.074 Ȁ 0.005%/h and 0.113 Ȁ 0.005%/h before and after the meal, respectively) after beef ingestion (P 0.001). Plasma amino acid concentrations peaked at Ȃ100 min after beef ingestion in both age groups but were substantially higher in the elderly (2185 Ȁ 134 nmol/mL compared with 1403 Ȁ 96 nmol/mL; P 0.001). Conclusion: Despite differences in the concentration of amino acids in the plasma precursor pool, aging does not impair the ability to acutely synthesize muscle protein after ingestion of a common protein-rich food.Am J Clin Nutr 2007;86:451-6.

It was clear that all three resistance training programs (isometric, concentric, and eccentric) in older adults were effective in increasing strength, concentric work, and concentric power over the 12-week training period. Furthermore, 12 weeks of resistance training resulted in improved stair ascent and descent performance.