Skeletal Muscle Mechanics during Exercise in Difficult environments Flashcards
Who are the 2 main contributors to the International Space Station (ISS)?
NASA and Russia (Russian space agency (RSA))
What is the gravity on Mars compared to Earth?
1/3
What are the physiological changes associated with a microgravity environment for > 15 days?
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)
What are the physiological changes associated with a microgravity environment similar to?
o Athletes in detraining (injury, cast, …)
o Reduced activity in older people
o Prolonged bed rest
What are the cardiovascular/cardiopulmonary changes associated with microgravity environments?
- 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
What are the hematology changes associated with microgravity environments?
- Reduced blood volume
- Suppressed erythropoiesis
What are the fluid and electrolyte changes associated with microgravity environments?
- 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
What are the muscle changes associated with microgravity environments?
Reduced loading and disuse of weight-baring tissues –>
- Muscle atrophy
- Altered muscle metabolism
- Altered muscle function
What are the bone changes associated with microgravity environments?
Reduced loading and disuse of weight-baring tissues –>
- Bone demineralization
- Altered calcium metabolism and calcitropic hormones
What are the neurosensory changes associated with microgravity environments?
- Altered vestibular function
- Altered sensory and balance information
- Space motion sickness
Which specific bones are lost in microgravity environment?
• 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)
Which muscles are more affected in microgravity environment?
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)
What causes a muscle atrophy during immobilization?
A decrease in protein synthesis for muscle regeneration or growth
Which type(s) of muscle fibers are lost during bed rest/microgravity? Which type is the most lost?
- 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.
What is lost in muscle during bed rest/microgravity?
- Changes in strength, volume and weight is similar in space missions and bed rest
Which exercise can help to do resistance training in space? How does it stimulate resistance training in the absence of gravity?
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
What did a study on flywheel show about muscle mass after bed rest?
- 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)
What happens to the calf muscle following prolonged bed rest ? How does pamidronate impact this?
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)
What happens to the BMD following prolonged bed rest ? How does pamidronate impact this?
BMD decreases with bed rest
- Exercise prevented decrease in BMD as much as pamidronate
Which markers of bone formation can we find in the serum?
Osteocalcin (BGP)
Bone-specific alkaline phosphatase
Procollagen peptides
Which markers of bone formation can we find in the urine?
Hydroxyproline
Hydroxylysine glycosides
Pyridinium crosslinks
Name 4 postural muscles
Postural muscles: Thigh and calf
Thigh: Vastus lateralis (part of quadricep group) and vastus intermedius
Calf: Soleus (fatigue resistant) and gastrocnemius
How does muscle force change after fatigue in flight animals as opposed to controls?
- 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)
How do different muscle fibers react to microgravity for 11-17 days in rats?
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)
How do different muscle fibers react to microgravity for 11-17 days in humans?
- 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
How do myofibrils change following 17 days of microgravity?
Disorganization of sarcomeres
Z band streaming, can rupture
Microarchitectural disorganization of sarcomeres
Loss of actin filaments
Which muscles lost CSA in bed rest in humans?
o Gluteal muscle (hip muscle; important when running for leg flexion) o Thigh o Knee extension o Calf o Ankle plantar flexor (tibial muscle)
How does skeletal muscle change after 6 months of ISS?
- 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
How does T1 fiber atrophy correlate with muscle volume?
- Correlation between type 1 fiber atrophy –> greater loss of muscle volume (CSA)
Although it does not explain the entire variation in muscle volume
What is 1-RM?
Maximum force isometric contraction that a muscle can produce without any shortening or velocity of contraction
What does Vmax represent?
- 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)
What does Po represent?
- Po will inform us on the force that a muscle group can generate, which is proportional to the CSA of the muscle
When does peak power occur?
peak power usually arrives at 30% of maximum force
How do force, velocity and power adapt top bed rest or limb suspension?
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
How does power change in individual muscle fibers following bed rest, in gastroc and soleus muscles?
- 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.
How do plantar flexion muscles change after microgravity?
- 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
How is muscle force velocity affected after 6 months ISS?
In calf: Significant difference in torque from isometric all along the velocities of shortening
How did exercise in the ISS (treadmill) relate to the muscle volume in 6 months ISS?
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
What happens to tendons after bed rest?
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
Why does plasma volume decrease in spaceflight? What is it characterized by clinically?
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
How does VO2 max change with microgravity environments?
- Max ability to consume oxygen decreases, then stabilizes after few weeks
What leads to a decrease in VO2max in spaceflights?
- 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))
Which muscle fibers are atrophied in short duration flights in rats and humans?
< 17 days
o Rats: Type I > Type II
o Humans: Type II > Type I
Which muscle fibers are atrophied in longer duration flights in humans?
• Long duration (> 6 months)
o Soleus Type I > Soleus Type II > Gastroc Type I > Gastroc Type II
How is the cardiovascular system affected by long-duration space missions?
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
