Fatigue Flashcards
Central fatigue
may involve central nervous system; broad effects in body
Local muscle fatigue
specific to a single/group of muscles (during acts of exercise)
Two common causes of muscle fatigue
-intramuscular acidosis (primarily accumulation of lactic acid)
-substrate depletion (primarily depletion of carbohydrates)
Lactic acid
lactate + hydrogen ion (H+)
When is lactic acid produced
when oxygen availability is limiting (all fiber types)
When oxygen is not limiting, in what fiber types is lactic acid still produced?
fast twitch fibers (type IIA and IIX)
As exercise intensity increases, more type IIX fiber are recruited, what happens with lactic acid?
lactic acid production increases
Anerobic metabolism helps when?
when oxygen usage plateaus, but the horse can still increase speed because of anerobic metabolism
-can also allow the horse to work beyond VO2 max
Lactic acid accumulation in blood occurs at its highest when?
when using anaerobic metabolism
Low rate of anaerobic metabolism:
-glycogen is broken down into glucose
-glycolytic metabolism turns glucose into ATP + lactic acid
-lactate and H+ ions move into the blood
-H+ ions are buffered by HCO3 and becomes carbonic acid
-carbonic acid is broken down into water and CO2
-water and CO2 go into the lungs
-CO2 is exhaled
High rate of anaerobic metabolism
-same process of low rate
-but H+ ions are produced too fast and start to accumulate in the blood
-bicarbonate (HCO3) concentration is depleted and H+ can no longer bind so it accumulates
-due to this the pH lowers
Lactic acid accumulates most for which types of exercise?
intense work for a short amount of time
Intramuscular acidosis:
at a high rate of anaerobic metabolism:
-after the blood pH drops
-movement of H+ ions into the blood slows down
-H+ starts to accumulate in the muscles
Fatigue from intramuscular acidosis is caused by:
-the accumulation of H+ ions in the muscles triggers a feedback response to stop breaking down glucose into ATP + lactic acid
-muscles can no longer contract as fast and the horse will have to slow down
-fatigue
Intramuscular acidosis is the primary cause of fatigue in what horses?
type IIX fibers and horses going at high speeds
What types of horses are more likely to deplete their muscle glycogen?
endurance horses
Who uses glycogen at a higher rate?
sprinters
Why would endurance horses deplete their muscle glycogen faster than sprinters?
because sprinters are using it at a higher rate, but only for 0.5-2 mins.
-endurance horses use it at a slow rate but for hours
In endurance type activities what should you want the muscles to use?
want to use fat and spare glycogen
-training and diet may help
What may help prevent carbohydrate depletion fatigue?
supplementation of carbohydrates during exercise (would lead to using more blood glucose which could spare muscle glycogen)
When is carbohydrate depletion not likely?
during most activities relying on anaerobic ATP synthesis (duration is too short)
When could carbohydrate depletion occur during short activities?
if muscle glycogen stores are low to begin with
Ex: 3 day eventing
Dehyrdration
result of fluid loss associated with sweating
-plasma volume decreases which decreases oxygen transport
Heat accumulation
-can effect muscle function
-can effect central nervous system function
Electrolyte imbalances
defects/disturbances in nerve and muscle function
Other causes of fatigue include:
-dehydration
-heat accumulation
-electrolyte imbalances
All interwoven with each other
