Acute and Chronic Adaptations - Physical Inactivity Flashcards
Consequences of Physical Inactivity
Muscle atrophy, weakness.
Muscular and neural adaptations.
What are the reasons for the weakness?
Decrease in muscle cross-sectional area and strength. 10-30% decrease in the first 30-40 days but is stabilized after 40 days.
Decrease in muscle force after 5 weeks of bed rest
in gastroc and soleus on average 46% decrease. However gastroc had a much larger decrease than soleus 51% vs 32% due to the fact that gastroc has much more of fast fibers than soleus.
Affects of bed rest on tendons
Increase in tendinous tissue compliance resulting in a decrease in installation of force.
What happens to maximal voluntary contractions (MVC) and tetanic contractions after forearm is placed in a cast for 6-8 weeks?
Decrease of MVC by 55%
Decrease in tetanic contractions of 30%.
What happens to maximal voluntary contractions (MVC) and tetanic contractions after 5 weeks of recovery (without any extra training) from a cast fracture?
There is still a 10% deficit of MVC and tetanic contractions.
Fast fibers (gastroc) vs Slow fibers (soleus) after 5 weeks of bed rest
Fast fibers decreased by 45% while slow only decreased by 10%.
During recovery slow fibers increase (more than before the bed rest), then decrease and increase again. While Fast fibers increase rapidly in the first week, increase slightly more and decrease slightly again.
Effects of 5 weeks bed rest on H-Reflex (soleus and gastroc)
Increase in H-reflex in both soleus and gastroc. Increase in excitation of motoneuron pools. Greater change in gastroc than soleus. Supports idea of neural adaptations especially for fast fibers.
Muscle atrophy at 4 and 8 weeks of cast and 10 weeks recovery
Progressive muscle atrophy at 4 and 8 weeks.
Muscle mass almost recovered at 10 weeks recovery.
Relationship between muscle atrophy and length of muscle
Loss of mass is greater when the muscle is held in a shortened position. Loss of sarcomeres and the muscle adapts to its new position.
Loss of Protein in Muscle Atrophy
Muscle atrophy is the loss of contractile protein.
Increase in contractile protein degradation.
Decrease in contractile protein synthesis.
Important protein loss in the first 15 days.
What are the possible answers to MN excitability increasing during immobilization?
Decrease in the inhibitory processes?
- presynaptic inhibition
- recurrent inhibition
Synergist activation
Increase in descending commands
How to diminish negative effects of immobilization?
30 maximal isometric contractions per day - maximal force preserved.
or cross adaptations.
