physiological and functional plasticity

what is physiological and functional plasticity

ability of muscles to change muscle fiber TYPE and composition in response to how and for what the organism uses its muscles

muscle fiber # is set

at birth

• 1° myotubes→ slow, oxidative (red) fibers

  • type 1

• 2° myotubes → fast, glycolytic (white) fibers

  • type 2’s

fibers change physiology in response to…

how muscle is used

changes occur in sequence

type 1→ type 2a→ types 2x/d→ type 2b

muscle fibers exist in …

dynamic flux of differing proportions of myosin type

innervation is key

muscle fibers respond to the stimulation they receive from motor nerves

tonic stimulation activates

oxidative muscle fibers

phasic stimulation activates

glycolytic muscle fibers

factors that affect muscle fiber type composition

• function

• species

• genetics

• age

• nutrition

• hormones

• use

• ambient temperature

• growth promoters

factors affect composition - species

same muscle anatomically in different species have different proportions of fiber types

factors affect composition - genetics

• artificial selection

  • domesticates (>type 2b) vs wildtype (>type 1)

• major genes

  • ex. halothane-sensitive pigs, myostatin-negative cattle

factors affect composition - age

majority of muscle fiber changes within muscles occur during early PERI-natal period

age - first muscle changeover

large increase in glycolytic fibers + small increase in oxidative fibers

• pre natal for cows; post natal for pigs

age - second muscle changeover

gradual increase in glycolytic fibers throuh full size + gradual decrease in oxidative fibers

factors affect composition - nutrition

severe malnutrition when young suppresses 2nd muscle fiber changeover

• results in < glycolytic and > oxidative fibers

factors affect composition - hormones

• testosterone: increase type 1/oxidative fibers

• thyroid: increase type 2/glycolytic fibers

factors affect composition - use

increase proportion of type 1 but style of exercis supersedes general use

• eg sprintin increases type 2/glycolytic fibers

factors affect composition - ambient temperature

long term hypothermia increases type 1/oxidative fibers

• due to shivering

factors affect composition - growth promoters

• beta adrenergic agonists increase type 2b/glycolytic