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PHGY 502 > Skeletal Muscle Mechanics during Exercise in Difficult environments > Flashcards

Skeletal Muscle Mechanics during Exercise in Difficult environments Flashcards

1
Q

Who are the 2 main contributors to the International Space Station (ISS)?

A

NASA and Russia (Russian space agency (RSA))

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2
Q

What is the gravity on Mars compared to Earth?

A

1/3

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3
Q

What are the physiological changes associated with a microgravity environment for > 15 days?

A

o Reduced BMD (osteopenia/osteoporosis)
o Disuse muscle atrophy
o Decreased plasma volume –> Decreased orthostatic tolerance (standing up in a gravity-exposed environment)
o Body mass and composition
o Kidney stones (loss of calcium in bone)

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4
Q

What are the physiological changes associated with a microgravity environment similar to?

A

o Athletes in detraining (injury, cast, …)
o Reduced activity in older people
o Prolonged bed rest

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5
Q

What are the cardiovascular/cardiopulmonary changes associated with microgravity environments?

A
  • Headward shift of leg fluid –> redistribution of circulating blood
    –>
  • Altered heart function and size
  • Altered BP function
  • Altered pulmonary function
    –>
    Reduced orthostatic tolerance, reduced max exercise capacity
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6
Q

What are the hematology changes associated with microgravity environments?

A
  • Reduced blood volume

- Suppressed erythropoiesis

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7
Q

What are the fluid and electrolyte changes associated with microgravity environments?

A
  • Altered kidney hemodynamics, altered urine flow and composition
  • Altered endocrine secterion
  • Altered plasma electrolytes, loss of intra- and extra-cellular fluids and salts
  • Loss of body water and salts
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8
Q

What are the muscle changes associated with microgravity environments?

A

Reduced loading and disuse of weight-baring tissues –>

  • Muscle atrophy
  • Altered muscle metabolism
  • Altered muscle function
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9
Q

What are the bone changes associated with microgravity environments?

A

Reduced loading and disuse of weight-baring tissues –>

  • Bone demineralization
  • Altered calcium metabolism and calcitropic hormones
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10
Q

What are the neurosensory changes associated with microgravity environments?

A
  • Altered vestibular function
  • Altered sensory and balance information
  • Space motion sickness
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11
Q

Which specific bones are lost in microgravity environment?

A 
•	Bone
o	Loss of 1% BMD per month at the spine
o	1-1.6%/month at the hip
- 0.4-0.5% of cortical BMD at hip
- 2.2-2.7% of trabecular BMD at the hip
o	2.6% loss of bone fracture strength (Increased bone fracture risk)
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12
Q

Which muscles are more affected in microgravity environment?

A

Postural muscles like calves and thighs.
o Loss of calf muscle volume, thigh muscle volume, knee, ankle and elbow muscles strengths
 Upper limbs are not as affected but still affected

o 2.2% loss of calf muscle volume/month (calf is a postural muscle related to gravity)
o 5.3% loss of peak calf muscle power/month (ability to generate force in time)

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13
Q

What causes a muscle atrophy during immobilization?

A

A decrease in protein synthesis for muscle regeneration or growth

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14
Q

Which type(s) of muscle fibers are lost during bed rest/microgravity? Which type is the most lost?

A
  • Loss of both slow-twitch (fatigue-resistant) and fast-twitch (fatigable) muscle fibres, but mostly fast-twitch!

–> muscle endurance decreases because fatigue resistant muscles decrease.

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15
Q

What is lost in muscle during bed rest/microgravity?

A
  • Changes in strength, volume and weight is similar in space missions and bed rest
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16
Q

Which exercise can help to do resistance training in space? How does it stimulate resistance training in the absence of gravity?

A

ESA flywheel training

Device can help for resistance training – designed to produce inertia (which still exists in a microgravity environment). –> produces microlesions in muscles which stimulates satellite cells = growth or maintenance of muscle fibre health

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17
Q

What did a study on flywheel show about muscle mass after bed rest?

A
  • Exercise group even increased their muscle mass compared to baseline
  • Control group had a greater loss in total BW during bed rest and after during recovery
    o Upon recovery, they recovered some BW (mainly water) but not all (net loss of muscle mass)
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18
Q

What happens to the calf muscle following prolonged bed rest ? How does pamidronate impact this?

A

Calf muscle CSA decreased.
Some people were given pamidronate (osteoclast inhibitor)
Osteoporosis medicine did not have any effect on calf muscle cross-sectional area, but exercise did have an effect (although still net loss)

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19
Q

What happens to the BMD following prolonged bed rest ? How does pamidronate impact this?

A

BMD decreases with bed rest

- Exercise prevented decrease in BMD as much as pamidronate

20
Q

Which markers of bone formation can we find in the serum?

A

 Osteocalcin (BGP)
 Bone-specific alkaline phosphatase
 Procollagen peptides

21
Q

Which markers of bone formation can we find in the urine?

A

 Hydroxyproline
 Hydroxylysine glycosides
 Pyridinium crosslinks

22
Q

Name 4 postural muscles

A

Postural muscles: Thigh and calf
Thigh: Vastus lateralis (part of quadricep group) and vastus intermedius
Calf: Soleus (fatigue resistant) and gastrocnemius

23
Q

How does muscle force change after fatigue in flight animals as opposed to controls?

A
  • In controls, animals were resistant to fatigue, only 20% decay in muscle force in 120s
  • In flight animals, they were less resistant to fatigue, nearly 60% drop in muscle force (less type 1 muscle fibers)
24
Q

How do different muscle fibers react to microgravity for 11-17 days in rats?

A

Rats:
o Soleus: Loss of Type 1 and Type 2 fibers
o Medium gastrocnemius muscle: Loss of Type 1 only
o Tibialis anterior: Increase in both type 1 and type 2 muscle fibers (no explanations on why… but is not a postural muscle)

25
Q

How do different muscle fibers react to microgravity for 11-17 days in humans?

A
  • Humans:
    o Vastus lateralis: Loss of all muscle fibre types (Type I, Type IIa, Type IIb)
    o Soleus: loss of Type 1, type 2a (fatigue-resistant)
    o Gastroc: Not as significant for maintaining posture, so not much change in any fibers
26
Q

How do myofibrils change following 17 days of microgravity?

A

Disorganization of sarcomeres
Z band streaming, can rupture
Microarchitectural disorganization of sarcomeres
Loss of actin filaments

27
Q

Which muscles lost CSA in bed rest in humans?

A 
o	Gluteal muscle (hip muscle; important when running for leg flexion)
o	Thigh
o	Knee extension
o	Calf
o	Ankle plantar flexor (tibial muscle)
28
Q

How does skeletal muscle change after 6 months of ISS?

A
  • Reduction in gastrocnemius and soleus cross-sectional area (CSA)
  • Type 1 muscle fibers most affected (significant reduction)
  • Gastroc: Increase in type II muscle fibers. There might be a decrease in type 1 that become type 2
  • Soleus: trend for muscle fibers change is similar but not statistically significant
29
Q

How does T1 fiber atrophy correlate with muscle volume?

A
  • Correlation between type 1 fiber atrophy –> greater loss of muscle volume (CSA)
    Although it does not explain the entire variation in muscle volume
30
Q

What is 1-RM?

A

Maximum force isometric contraction that a muscle can produce without any shortening or velocity of contraction

31
Q

What does Vmax represent?

A
  • Vmax: With extrapolation to zero load, maximum muscle velocity of contraction

Can give us an idea of muscle fiber composition without being as invasive as a biopsy
o High Vmax: Higher composition of type 2 muscle fibers (e.g. higher jump in an individual)

32
Q

What does Po represent?

A
  • Po will inform us on the force that a muscle group can generate, which is proportional to the CSA of the muscle
33
Q

When does peak power occur?

A

peak power usually arrives at 30% of maximum force

34
Q

How do force, velocity and power adapt top bed rest or limb suspension?

A

Adaptations that increase contractile velocity (slow to fast shift) to counter some of the loss in force production capability
- Po is reduced with bed rest
- Peak power is slightly left of the curve; still occurring at about 30% of maximal force
o Po is reduced but peak velocity does not seem to be affected; can still produce slightly same maximal power

35
Q

How does power change in individual muscle fibers following bed rest, in gastroc and soleus muscles?

A
  • In single muscle fibers, there is a reduction in peak power in type I muscle fibers in gastroc and soleus muscles
  • In type II muscle fibers, in the same muscle groups, peak power also goes down
  • In type II muscle fibers (gastroc only), Po is not affected
  • In soleus type II fibers, Po IS affected.
36
Q

How do plantar flexion muscles change after microgravity?

A
  • Reduction of about 20-30% at Po for triceps surae (plantar flexion)
  • At different velocities of contraction, the change is significant (decrease in longer space flight)
  • From isometric contraction to dynamic/high velocity contraction, there was a loss of force in both plantar flexors and dorsiflexors
37
Q

How is muscle force velocity affected after 6 months ISS?

A

In calf: Significant difference in torque from isometric all along the velocities of shortening

38
Q

How did exercise in the ISS (treadmill) relate to the muscle volume in 6 months ISS?

A

For those who trained on the treadmill during the ISS, Amount of exercise on the treadmill is correlated with muscle loss. Greater exercise on the treadmill = less muscle loss

39
Q

What happens to tendons after bed rest?

A

They become less stiff with bed rest
Stiffness decreases less with exercise and bed rest, but still decreases vs baseline
o 37% reduction in tendon stiffness in BREx
o 58% reduction in tendon stiffness in BR

Young’s modulus (measurement of tendon elasticity) also decreases in the same pattern = more without exercise.
o Even though the tendon is stiffer in the exercise group, it still has a good amount of elasticity, meaning that it will come back to initial position when stretched
o Elasticity decreased less in BREx group, meaning also less risk of Achilles tendon rupture

40
Q

Why does plasma volume decrease in spaceflight? What is it characterized by clinically?

A

Fluid shifts from the lower to the upper part of the body. This thoraco-cephalic fluid shift stimulates central volume carotid, aortic and cardiac receptors inducing an increase in diuresis and natriuresis and a decrease in plasma volume. As in spaceflight, cardiovascular and deconditioning characterized by orthostatic intolerance is observed at the end of bedrest

41
Q

How does VO2 max change with microgravity environments?

A
  • Max ability to consume oxygen decreases, then stabilizes after few weeks
42
Q

What leads to a decrease in VO2max in spaceflights?

A
  • Part of this reduction is related to QO2 (cardiac output)
  • Arterial venous O2 content is reduced
  • Decrease in DO2 (Diffusive (o2 leaving capillaries to diffuse in mitochondria to be consumed by body))
43
Q

Which muscle fibers are atrophied in short duration flights in rats and humans?

A

< 17 days
o Rats: Type I > Type II
o Humans: Type II > Type I

44
Q

Which muscle fibers are atrophied in longer duration flights in humans?

A

• Long duration (> 6 months)

o Soleus Type I > Soleus Type II > Gastroc Type I > Gastroc Type II

45
Q

How is the cardiovascular system affected by long-duration space missions?

A

Initial increases in cardiac volume that decreases with mission duration
Unchanged resting cardiac output
Decreased sub-maximal stroke volume and cardiac output
Progressive decrease in cardiac max

PHGY 502 (6 decks)

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