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Skeletal muscle mass declines with inactivity (casting is a good example) and increases with activity (such as weightlifting). Whether muscle mass increases or decreases, is determined by whether more new proteins within muscle are made than are broken down. The investigators know that feeding protein increases the synthesis of new proteins but that the response of older muscles to protein feeding is blunted compared with the young. This resistance of the elderly to muscle building stimuli may be the primary reason that muscle mass is lost in aging. The investigators also know that periods of muscle disuse such as casting result in a person's muscle shrinking due, the investigators believe, to a lower rate of synthesis of new muscle proteins. Age-related muscle loss begins around 50 years old and proceeds at approximately 1% for every year after. Elderly persons would likely fare well with advancing age if their muscle loss were simply linear; however, a rate of muscle loss of 1% annually is a 'population view' and does not represent what occurs during short periods of muscle disuse (i.e. during hospitalization or illness), which occur with increasing frequency in elderly persons. During periods of disuse, the resistance of elderly muscles to protein nutrition may be worsened. The investigators will measure how quickly new proteins are made at rest and after protein feeding in elderly men, before and after a 14 day period of reduced activity brought on by having people reduce their daily step count.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Step Reduction | Experimental | Step reduction:
|
|
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Step reduction | Behavioral | taking less than 1500 steps/d |
|
| Measure | Description | Time Frame |
|---|---|---|
| Fractional synthetic rate (FSR) of myofibrillar muscle protein | rate of making new muscle proteins | over 5h |
| Measure | Description | Time Frame |
|---|---|---|
| Blood amino acid concentrations | concentration of amino acids in blood | over 5h |
| Intramuscular signalling protein status | phosphorylation of key signalling proteins |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Affiliation | Role |
|---|---|---|
| Stuart M Phillips, PhD | McMaster University | Principal Investigator |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| McMaster University | Hamilton | Ontario | L8S 4K1 | Canada |
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| ID | Term |
|---|---|
| D055948 | Sarcopenia |
| D007333 | Insulin Resistance |
| ID | Term |
|---|---|
| D009133 | Muscular Atrophy |
| D020879 | Neuromuscular Manifestations |
| D009461 | Neurologic Manifestations |
| D009422 | Nervous System Diseases |
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| over 5h |
| Insulin sensitivity via blood sampling | measure of insulin concentration | over 5h |
| D001284 | Atrophy |
| D020763 | Pathological Conditions, Anatomical |
| D013568 | Pathological Conditions, Signs and Symptoms |
| D012816 | Signs and Symptoms |
| D006946 | Hyperinsulinism |
| D044882 | Glucose Metabolism Disorders |
| D008659 | Metabolic Diseases |
| D009750 | Nutritional and Metabolic Diseases |