Muscle Mass During Space Exploration

Not Applicable

Completed

Brief Summary: The investigators will test the following hypotheses:

1. Bedrest will blunt the anabolic response to a mixed nutrient meal, facilitating a loss of muscle mass and functional capacity that is only partially restored during rehabilitation.

2. Enriching daily meals with leucine will promote protein synthesis and maintain the anabolic response to mixed nutrient meal ingestion. This will preserve lean muscle mass and function during bedrest and facilitate the recovery of functional and metabolic capacity during rehabilitation.

Detailed Description: Our long-term goal is to identify, prevent and remedy defects in the metabolic pathway that contribute to the loss of muscle mass and function during exposure to microgravity. Demographic data indicate that the average age of shuttle crew members has increased from 40.7 yrs in 1995 to 46.7 yrs in 2007 with an increasing number of astronauts over 50 yrs of age. We contend that the loss of muscle mass and function during spaceflight is facilitated by an age-associated, progressive impairment in the ability to mount an anabolic response to standard mixed nutrient meals. We propose that enriching daily meals with a low-volume leucine supplement will reduce the deleterious effects of microgravity on skeletal muscle and facilitate recovery during rehabilitation.

We will employ our established 14 day bed rest protocol to model the skeletal muscle unloading that occurs during microgravity. We will also examine recovery of muscle mass and functional capacity during a 7 day rehabilitation period. We will study 2 groups: CON (Bedrest/Recovery + Placebo; n=15), LEU (Bedrest/Recovery + Leucine; n=15). We will assess a) markers of translation initiation, b) muscle protein synthesis, c) muscle mass and body composition and d) strength and aerobic capacity.

Recruitment & Eligibility

Inclusion Criteria

Exclusion Criteria

Subjects with cardiac abnormalities considered exclusionary by the study physicians
Subjects with uncontrolled metabolic disease
A GFR <65 mL/min/1.73m2 or evidence of kidney disease or failure
Subjects with vascular disease or risk factors of peripheral atherosclerosis
Any history of hypo- or hyper-coagulation disorders. (e.g., Coumadin use or history of DVT or PE)
Subjects with chronically elevated systolic pressure >150 or a diastolic blood pressure > 100
Subjects with implanted electronic devices (e.g., pacemakers, electronic infusion pumps, stimulators)
Subjects with recently (6 months) treated cancer other than basal cell carcinoma
Any subject currently on a weight-loss diet or a body mass index > 30 kg/m2
Inability to abstain from smoking for duration of study
A history of > 20 pack per year smoking
Any subject that is HIV-seropositive or has active hepatitis
Recent anabolic or corticosteroids use (within 3 months)
Subjects with hemoglobin or hematocrit lower than accepted lab values
Agitation/aggression disorder
History of stroke with motor disability
A recent history (<12 months) of GI bleed
Any other condition or event considered exclusionary by the PI and faculty physician