Loss of skeletal muscle strength and skeletal muscle mass occurs with of aging. This are-related decline in skeletal muscle mass and skeletal muscle strength is a major underlying factor contributing to many of the metabolic disorders and frailty of the investigators rapidly expanding aging population. Endurance (aerobic) and resistance exercise training programs have been shown to effectively reverse the age-related decline in metabolic and contractile muscle functions. The investigators will measure synthesis rates of individual muscle proteins in 36 each of young (18-30 yrs) and 36 older (> 65 yrs) people to determine their response to 8 weeks each of endurance, resistance, combined endurance and resistance training, or placebo exercise training.

Hypotheses.

1. to measure fractional synthesis rates of multiple muscle proteins and identify those that are enhanced by an endurance exercise program
2. to determine whether changes in protein synthesis in response to endurance exercise programs are dependent on age
3. to measure fractional muscle synthesis rates of multiple muscle proteins and to identify those that are enhanced by a resistance exercise program
4. to determine whether changes in protein synthesis in response to resistance exercise programs are dependent on age

Inclusion Criteria:

• Healthy
• 18 to 30 or >65 years
• Males and Females

Exclusion Criteria:

• Regular Exercise Program
• Smoking
• Cardiometabolic Disease (diabetes, cardiovascular disease, thyroid disorders)
• Drugs known to impair metabolic function (beta blockers, steroids)
• Allergies to lidocaine
• Physical disability that precludes exercise