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18 Cards in this Set
- Front
- Back
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Average life expectancy
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about 80 years
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What % of the population over 65 by 2020?
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18%
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% of adults who report little or no leisure time activity?
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about 60%
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What is sarcopenia?
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age-related change in skeletal muscle. (literally, reduction in amount of flesh.)
It is both the reduction in muscle mass (CSA), as well as more intramuscular and subcutaneous fat. |
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Statistics of muscle loss
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After age 30, 15% loss of muscle mass per year
By 75, only 30% muscle mass left (of mass when young) |
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Factors contributing to sarcopenia
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- muscle atrophy
- reduced # motor units - changes in CNS - altered muscle contractility - humoral factors: - altered enzyme activity levels - endocrine changes - Lifestyle factors - decreased physical activity - poor nutrition and/or disease |
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When does age-related decrease in strength appear?
What is the rate of decline? |
about 60 years
1.5% decline in strength each year after 60. |
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Age-related strength changes and types of contractions
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Decreases in strength of isometric and concentric contractions.
Less decrease in strength of eccentric contractions. |
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Decreased sarcomere number
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leads to:
- decrease in velocity of shortening - shortening of cells (and thus muscles) - less optimal length-tension relationship |
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Decreased sensitivity of DHPR receptors
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leads to attenuation of Ca++ release
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Age-related cellular changes
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- decreased # sarcomeres
- decreased density of DHPR receptors - reduced SR activity |
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Age-related changes at preterminal neuron
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- spherical swellings on axons
- axonal sprouting - collateral innervation |
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Age-related changes at post-synaptic neuron
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- widening of secondary synaptic clefts
- shallowing of primary synaptic clefts - increased collagen content ** no change in ACh sensitivity ** |
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Age-related loss of fiber type
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30% loss by age 80.
Both type I and II are lost. More type II are lost. Increase in relative percentage of type I fibers. Loss of fiber type is a denervation process. Loss of type II - programmed cell death? extrinsic factors? |
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Age-related changes in motor units
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1/2 amount of functioning motor units by age 70.
More muscle fibers per motor unit (due to collateral innervation). |
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Age-related changes in conduction velocities
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- decreased firing rates.
- decreased conduction velocities. - decreased internodal length (due to demyelination) - slower time to peak tension/relaxation time. --> summation happens at lower intensities. |
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Age-related changes in central activation
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Deficits vary from muscle to muscle.
Burst imposition tests show that older people can activate motor units as effectively as younger people. --> Neural drive does not limit strength in aging. |
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Three major reasons why aging muscle is weak
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1. Decreased number of fast twitch fibers.
2. Decreased fiber size. 3. Decreased number of motor units. |
