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18 Cards in this Set

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Average life expectancy
about 80 years
What % of the population over 65 by 2020?
18%
% of adults who report little or no leisure time activity?
about 60%
What is sarcopenia?
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.
Statistics of muscle loss
After age 30, 15% loss of muscle mass per year

By 75, only 30% muscle mass left (of mass when young)
Factors contributing to sarcopenia
- 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
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.
Age-related strength changes and types of contractions
Decreases in strength of isometric and concentric contractions.

Less decrease in strength of eccentric contractions.
Decreased sarcomere number
leads to:
- decrease in velocity of shortening
- shortening of cells (and thus muscles)
- less optimal length-tension relationship
Decreased sensitivity of DHPR receptors
leads to attenuation of Ca++ release
Age-related cellular changes
- decreased # sarcomeres
- decreased density of DHPR receptors
- reduced SR activity
Age-related changes at preterminal neuron
- spherical swellings on axons
- axonal sprouting
- collateral innervation
Age-related changes at post-synaptic neuron
- widening of secondary synaptic clefts
- shallowing of primary synaptic clefts
- increased collagen content

** no change in ACh sensitivity **
Age-related loss of fiber type
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?
Age-related changes in motor units
1/2 amount of functioning motor units by age 70.

More muscle fibers per motor unit (due to collateral innervation).
Age-related changes in conduction velocities
- decreased firing rates.
- decreased conduction velocities.
- decreased internodal length (due to demyelination)
- slower time to peak tension/relaxation time.

--> summation happens at lower intensities.
Age-related changes in central activation
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.
Three major reasons why aging muscle is weak
1. Decreased number of fast twitch fibers.
2. Decreased fiber size.
3. Decreased number of motor units.