The Impact of Biological Mechanisms of Aging on Response Variability to Resistance Training in Older Adults

Inclusion Criteria: * aged greater than or equal to 65 years * sedentary (Community Healthy Activities Model Program for Seniors physical activity questionnaire to identify and exclude persons engaged in regular (125 min/week or more) moderate intensity physical activity * at risk for mobility disability score of less than or equal to 10 (but greater than 3) on the SPPB * willing to be randomized into HE or PRT * willing to be transported or transport themselves to the clinical sites for the intervention and assessments Exclusion Criteria: * unwillingness to provide informed consent * participation in lifestyle or pharmacologic intervention trial or structured program of exercise training in the past 6 months * an SPPB score of less than or equal to 3 * osteoarthritis or condition with joint pain limiting daily life activities * significant weight loss or gain (7.5% of body weight) in past six months * current anti-coagulant or anti-platelet therapy (Coumadin, Eliquis, Pradaxa, Xarelto, heparin, Lovenox, Plavix) * clinically significant abnormality in any of the screening laboratory values, including those identified as outside of the "normal limits', that are deemed to be of concern for participation in the study by the study physician * acute or terminal illness * Mini Mental State Exam (MMSE) \<23 * myocardial infarction in the previous 6 months or other symptomatic coronary artery disease * New York Heart Association Class III or IV congestive heart failure * serious conduction disorder (e.g., 3rd degree heart block), uncontrolled arrhythmia, or new Q waves or ST-segment depressions (\>3 mm) on ECG * chronic obstructive pulmonary disease requiring oxygen therapy * upper or lower extremity fracture in the previous 6 months * uncontrolled hypertension (150/90 mm Hg) * neuromuscular diseases and/or drugs which affect neuromuscular function * current use of anabolic steroids, growth hormone, replacement androgen therapy, anti-androgen therapy * allergy to lidocaine * presence of significant liver or renal disease (eGFR \< 45 mL/min) * diagnosis of type I diabetes mellitus or insulin requiring type 2 diabetes mellitus * HbA1c \> 7% * BMI \<21 or \>35 for men or \>40 for women * excessive alcohol intake (\>14 alcoholic beverages per wk.) * current tobacco use * current participation in any interventional clinical trial * current use of weight loss medications