Several trials have found that nutritional supplementation can elicit an increased rate of skeletal muscle protein synthesis following a single bout of exercise in both young and older individuals. However, there have been no studies that have investigated if nutritional supplementation and exercise can cause a sustained increase in physical functioning and fat free mass, particularly in older adults with functional limitations. This study will compare the effects of a nutritional supplement versus a placebo on exercise training induced changes in physical functioning older adults who are at risk for mobility disability.

Exercise Intervention: Participants will complete exercise sessions 3 times per week for 6 months. The exercise sessions will involve walking, lower extremity strength exercises, flexibility, and balance training.

Supplement Intervention: Participants will be randomly assigned to receive either the nutritional supplement or placebo. The participants will consume on beverage immediately after each exercise session.

Primary Outcome: The primary outcome will be the time to walk 400 meters, expressed as average gait speed during the 400 M walk. All participants must be able to walk 400 meters in <15 minutes at walking at their normal speed. The 400 M walk will be assessed at baseline, 3-months, and 6-months, with the changes at 6-months being the primary outcome.

Secondary Outcome Measures:

• Stair Climb Test
• Body Composition
• Skeletal muscle cross sectional area
• Isokinetic/Isometric peak torque/power
• Hand-grip strength
• Nutritional status
• Quality of Life/Depressive symptoms Expected enrollment: 150 (80 at Tufts University (Boston, MA, USA), 70 at University of Uppsala (Uppsala, Sweden))

Inclusion Criteria:

1. Male & Female ≥ 70 yrs
2. Community dwelling
3. Short Physical Performance Battery ≤ 9
4. Willingness to be randomized and come to the laboratory for 6 months
5. Body Mass Index < 35
6. Mini-Mental State Examination >=24
7. Serum 25 (OH) D (22.5 -50 nmol/l)
8. Having obtained his/her informed consent
9. Able to complete 400 M walk within 15 minutes

Exclusion Criteria:

• • Acute or terminal illness; terminal illness with life expectancy less than 12 months, as determined by a physician

  • Current regular use (> 1 per week) of high protein oral nutritional supplements (eg: Boost, Exceed etc…)
  • Current use of Vitamin D supplements, >800 IU/day
  • Myocardial infarction in previous 6 months, symptomatic coronary artery disease, or congestive heart failure.
  • Upper or lower extremity fracture in previous 6 months.
  • Hemoglobin < 10 g/dL, Estimated GFR < 30 mL/min/1.73 m2
  • Uncontrolled hypertension (>150/90 mm Hg).
  • Neuromuscular diseases and drugs which affect neuromuscular function; severe progressive, degenerative neurologic disease
  • Hormone replacement therapy
  • Insulin-dependent diabetes mellitus
  • Milk protein allergy
  • Major surgery in the past 6 months (requiring general anesthesia)
  • Other significant co-morbid disease that would impair ability to participate in the exercise-based intervention, e.g. renal failure on hemodialysis, severe psychiatric disorder (e.g. bipolar, schizophrenia)
  • Excessive alcohol use (>14 drinks per wk)
  • Participation in moderate intensity physical activity > 20 minutes/week
  • Inability to communicate due to severe, uncorrectable hearing loss or speech disorder
  • Severe visual impairment (if it precludes completion of assessments and/or intervention)
  • Severe rheumatologic or orthopedic diseases, e.g., awaiting joint replacement, active inflammatory disease; wheelchair bound
  • Cancer requiring treatment in the past three years, except for non-melanoma skin cancers or cancers that have clearly been cured or in the opinion of the investigator carry an excellent prognosis (e.g., Stage 1 cervical cancer)
  • Severe pulmonary disease, requiring either steroid pills or injections or the use of supplemental oxygen
  • Severe cardiac disease, including NYHA Class III or IV congestive heart failure, clinically significant aortic stenosis, history of cardiac arrest, use of a cardiac defibrillator, or uncontrolled angina
  • Patient who cannot be expected to comply with treatment, as decided by the Principal Investigator and study physician.
  • Conditions not specifically mentioned above may serve as criteria for exclusion at the discretion of the clinical site Principal Investigator and/or study physician.