Using stable isotope methodology, investigators will determine the postabsorptive and postprandial muscle protein synthetic response in 60 female adults (Age 50-79, BMI: <30 kg/m2) immediately after an acute bout of resistance exercise. Participants will be divided in to 5 groups of twelve women (n=12). Each group will receive a different protein beverage or placebo to consume following the resistance exercise training. Group 1 will consume a beverage consisting of whey protein; group 2 will consume whey protein supplemented with additional leucine; group 3 will consume whey protein supplemented with additional leucine and hydrolyzed whey peptides; group 4 will consume whey protein supplemented with additional leucine and citrulline; group 5 will just consume water. During the testing, blood and muscle samples will be collected.

Inclusion Criteria:

• BMI <30 kg/m2
• Healthy, sedentary
• Either 20-30 years old or 50-79 years old

Exclusion Criteria:

• Tobacco use
• Allergies to milk consumption
• Unusually high protein consumption
• Vegan diet
• Allergies to antibiotics or xylocaine
• Phenylketonuria (PKU)
• Diagnosed GI tract diseases
• Arthritic conditions
• A history of neuromuscular problems
• Heart disease
• Metabolic disorders
• -Liver, kidney, or urinary disease
• Musculoskeletal problems
• Autoimmune disease
• Neurological disease
• Previous participation in amino acid tracer studies
• Predisposition to hypertrophic scarring or keloid formation
• Individuals on any medications known to affect protein metabolism (i.e. corticosteroids, non-steroidal anti-inflammatories, or prescription strength acne medications).
• Individuals using thyroid medications or other medications affecting endocrine function
• Pregnancy
• Contraindications for exercise
• BMI ≥30
• supplements that influence protein metabolism (e.g omega 3 fish oils)