PET 4067 Physical Dimensions of Aging st...
PET_4067_Physical_Dimensions_of_Aging_study_guide_2.docx-Physical Dimensions of Aging Study Guide
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PET 4067 Physical Dimensions of Aging study guide ...
PET_4067_Physical_Dimensions_of_Aging_study_guide_2.docx-Physical Dimensions of Aging Study Guide
PET 4067 Physical Dimensions of Agi...
PET_4067_Physical_Dimensions_of_Aging_study_guide_2.docx-Physical Dimensions of Aging Study Guide
Page 1
Physical Dimensions of Aging
Study Guide 2
Muscle Study Guide
1. What is the time course of muscle mass loss?
What is the difference in the slow and fast
Slow phase (10% loss): losses in muscle mass from the age of 25-50
Fast phase (40% loss): losses in muscle mass from age 50+
Up to 15% loss each decade after 70
What is the definition of sarcopenic?
2 standard deviations below the average muscle mass of a 20-30-year-old
3. Why is muscle important?
Regulation of metabolism, site for glucose disposal, amino acid storage (conditions of
starvation), thermoregulation, endocrine organ (skeletal muscle makes things that are
secreted into the body and affect other organs), exosomes (releasing factors out into
circulation to other organs)
4. What is muscle atrophy?
Decrease in muscle fiber size with aging
~10-40% decrease in muscle fiber cross sectional area (fiber size)
Mostly type 2 fibers
What is meant by positive and negative nitrogen balance?
Positive: breakdown < synthesis (growth state, like a young child)
Negative: synthesis< breakdown (atrophy state, like starvation)
What are the contractile proteins?
Actin and myosin
What is meant by fed gains and is it similar between young and old individuals?
Fed gains: the area under the curve when you increase protein synthesis after a meal
As long as the fed gains are = to the fasted losses, then the muscles will remain
the same size
Young and old individuals: in the fasted state, young and elderly individuals had a similar
rate of protein synthesis. After amino acids and glucose, the rate of protein synthesis in
the young individuals increased, but the elderly stayed the same
Fed gains are not occurring in the elderly individuals
The rate of synthesis in elderly individuals plateau’s (maxes out) at an earlier

Page 2
What muscle fibers are lost preferentially during the aging process? Type I or Type II?
Changes in muscle composition with aging contribute to muscle atrophy
With aging, there is evidence that aging increases the percentage of type 1muscle
The loss of fiber number (particularly type 2) can equal 30-40% by 80 years of
Evidence of impaired protein synthetic response to resistance exercise
Young adults increased muscle protein synthesis to a greater extent
compared to older adults
This means that the shift in protein balance may not be great enough= less
The muscle cannot produce as much force in older individuals
What is dynapenia?
Age related loss in strength
Strength decreases in a similar timeline that muscle mass does
Do losses in muscle strength correlate with losses in muscle mass?
Change in strength is not only caused by a loss of muscle mass
You lose strength at a faster rate than you lose mass
11. How are muscle fibers recruited when you lift something heavy?
Type 1
Type 2a
Type 2x
Motor neurons of aged individuals show a slower rate of firing
The inability to fully recruit muscle fibers, particularly type 2 fibers that are still
present, is dictated by the rate at which the muscle fiber is stimulated by the motor
12. Know what is meant by a twitch, summation, and tetanus.
Is it different between type I and
II muscle fibers?
Summation: the addition of muscle force from a stimulation on top of the force generated
by a previous stimulation
One single stimulation to the muscle will generate a twitch
Generation of force that goes up and comes down to its baseline level
By stimulating the muscle a second time before force comes back down to
baseline, you get summation
If you stimulate the muscle fast enough, you will summate the force to a peak,
which is called tetanus (the maximal force that muscle can generate)
Type 1: can reach tetanus at a lower stimulation frequency
Type 2: requires a faster rate of stimulation to maximize force production (tetanus)
13. Why is an aged muscle not as strong as a young muscle? Be able to name factors that are
causing this decrease at the neural and cellular level.
Neural changes that lower muscle strength: there is evidence that aged individuals show
cognitive decline characterized by the inability to initiate voluntary muscle contraction
from the motor cortex= less muscle force

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