This study is investigating changes to the proteins in skeletal muscle that contribute to reduced muscle size and muscle function that occurs with aging.

Age-related muscle atrophy and contractile dysfunction have been well described at the cellular level, but the molecular mechanisms that contribute to this dysfunction are poorly understood. Improved understanding of these mechanisms is critically important for the improvement of physical rehabilitation in older adults at risk for mobility impairment and physical disability. Our studies will pursue pre-clinical evidence that post translational modification of specific proteins in skeletal muscle lead to an "aging phenotype" in skeletal muscle that may unlock new strategies for improving physical function in older adults with physical frailty.

Inclusion Criteria:

• Adults between the ages 18-35 or 65-80 years
• Healthy by self-report
• Willing to participate in all aspects of the study design including muscle biopsy, unilateral exercise, and physical activity monitoring
• Fluent in English (due to lack of translation services, it is not practical to conduct the study using a language other than English).

Exclusion Criteria:

• Orthopaedic limitation (severe knee osteoarthritis, prior joint replacement, etc.).
• Volunteer has dementia or related mental issues that potentially put the subject at risk as determined by prior diagnosis.
• Volunteer has known untreated endocrine disease (hypo/hyper thyroidism, Addison's Disease or Cushing's syndrome, etc.)
• Volunteer has untreated/poorly-controlled hypertension (stage 2, per American College of Cardiology [>140/90 mmHg]).
• Volunteer has significant heart, liver, kidney or respiratory disease.
• Volunteer has diabetes (insulin dependent or non-insulin dependent).
• Volunteer has known coagulopathies.
• Volunteer has taken anabolic steroids in the prior six months.
• Volunteer has received treatment for cancer (other than effective Mohs Surgery for successful removal of basal cell or squamous cell carcinomas)
• Unexpected weight loss >5kg is last 12 months
• Volunteer is an active smoker or quit within the last year.
• Volunteer has known current alcohol or drug use disorder (AUD; defined as binge drinking of >4 days in the last month. Binge drinking is >5 drinks for men and >4 drinks for women, per occasion). Or, if a volunteer reports drinking in excess of "low risk" per NIAAA (>7 drinks/week for men and >3 drinks/day for women and >14 drinks/week and >4 drinks/day).
• Volunteer has a diagnosed neuromuscular disorder.
• Volunteer has allergy to lidocaine.