Exam 3- Lecture 20

Question 1

Spectrum of disease

Answer 1

reduced activity –> bedrest, microgravity –> casting –> SPI

Question 2

What decreases initially when highly trained athletes are detrained?

Answer 2

• SV due to early blood volume loss

- dextran (antithrombotic) can reverse fall in SV

Question 3

what is slower to reverse when highly trained athletes detrain?

Answer 3

• a-v O2 difference

- takes about 3 months for capillary density and mitochondrial activity to decrease

Question 4

how quickly does VO2max reverse with detraining after short term training (10 weeks)

Answer 4

• complete in 8-12 weeks

- initial fall is due to decreased SV

Question 5

what occurs after 3 months of detraining after a short term training (10 weeks)

Answer 5

• mitochondrial enzyme content completely returns to sedentary levels
• capillary density reverses partially to fully

Question 6

do structural or functional adaptations persist longer?

Answer 6

structural adaptations

Question 7

Long term MAY result in ….

Answer 7

structural adaptations that persists for “long” periods of time

Question 8

How long does it take for VO2 max to decrease with bedrest?

Answer 8

20 days

Question 9

explain the physiologic process that happens with bed rest:

Answer 9

supine position –> shift in blood volume to thoracic cavity –> stimulates atrial volume receptors can either:
increase ANP –> H2O excretion –> fall in plasma volume –> lower SV and VO2 max
OR
reflexively inhibit ADH and renal SNA –> increases sodium excretion –> fall in plasma volume –> lower SV and VO2 max

Question 10

Cardiovascular consequence of bed rest

Answer 10

Reduced orthostatic tolerance:

• tendency to faint when standing
• reduced submaximal exercise tolerance

Question 11

explain why people who have been on bed rest have a tendency to faint when standing

Answer 11

• lower plasma volume

- increase venous compliance due to excess CO stored in venous circulation

Question 12

explain why people who have been on bedrest have reduced tolerance to submaximal exercise

Answer 12

• decreased exercise time
• due to decrease in enzymatic oxidative capacity
• higher HR at submax intensities

Question 13

Muscular adaptations to disuse (casting)

Answer 13

• some neural and isometric tension can occur

- muscle atrophy

Question 14

what is muscle atrophy

Answer 14

reduction in muscle size primarily through reduction in contractile proteins

Question 15

does atrophy occur faster in disuse or detraining

Answer 15

disuse

Question 16

degree of immobilization- induced atrophy is related to:

Answer 16

• degree of disuse or immobilization
• initial level of use –> most used get most atrophic
• duration of immobilization

Question 17

what is muscle strength loss (due to disuse) correlated with?

Answer 17

• reduction in cross sectional area

- peaks at 6 months

Question 18

What is the metabolic response to disuse?

Answer 18

• reduction in oxidative capacity and glycogen storage
• increased fatigability
• subtype reverts to pre-training fiber distribution

Question 19

what does unloading a lower limb muscle to 5 weeks do?

Answer 19

• increases vulnerability to eccentric-exercise induced injury
• injury during reloading phase in rehab may be sufficient to prolong recovery
• emphasizes the use of low intensity exercise during the initial return to ambulation

Question 20

irradiation

Answer 20

bilateral corticospinal activity occurs with intentional unilateral muscle activation via corpus callous and pyramidal decussation

Question 21

what can maintain mitochondrial function and attenuate atrophy after immobilization?

Answer 21

heat

Question 22

what occurs to calcium metabolism with disuse?

Answer 22

• balance between new bone formation and resorption is disrupted by prolonged bed rest, immobilization, weightlessness

Question 23

Changes in BMD with detraining

Answer 23

occurs in adults > 50 years old
cessation of regular weight bearing exercise
may result in decreased spine BMD back to sedentary levels

Question 24

Is disuse osteopenia reversible?

Answer 24

• yes –> takes days
• BMD changes take much longer –> 5-10x longer than immobilization period
• long term disuse osteopenia may result in a permeant reduction in BMD