Fatigue

Question 1

Central fatigue

Answer 1

may involve central nervous system; broad effects in body

Question 2

Local muscle fatigue

Answer 2

specific to a single/group of muscles (during acts of exercise)

Question 3

Two common causes of muscle fatigue

Answer 3

-intramuscular acidosis (primarily accumulation of lactic acid)
-substrate depletion (primarily depletion of carbohydrates)

Question 4

Lactic acid

Answer 4

lactate + hydrogen ion (H+)

Question 5

When is lactic acid produced

Answer 5

when oxygen availability is limiting (all fiber types)

Question 6

When oxygen is not limiting, in what fiber types is lactic acid still produced?

Answer 6

fast twitch fibers (type IIA and IIX)

Question 7

As exercise intensity increases, more type IIX fiber are recruited, what happens with lactic acid?

Answer 7

lactic acid production increases

Question 8

Anerobic metabolism helps when?

Answer 8

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

Question 9

Lactic acid accumulation in blood occurs at its highest when?

Answer 9

when using anaerobic metabolism

Question 10

Low rate of anaerobic metabolism:

Answer 10

-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

Question 11

High rate of anaerobic metabolism

Answer 11

-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

Question 12

Lactic acid accumulates most for which types of exercise?

Answer 12

intense work for a short amount of time

Question 13

Intramuscular acidosis:

Answer 13

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

Question 14

Fatigue from intramuscular acidosis is caused by:

Answer 14

-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

Question 15

Intramuscular acidosis is the primary cause of fatigue in what horses?

Answer 15

type IIX fibers and horses going at high speeds

Question 16

What types of horses are more likely to deplete their muscle glycogen?

Answer 16

endurance horses

Question 17

Who uses glycogen at a higher rate?

Answer 17

sprinters

Question 18

Why would endurance horses deplete their muscle glycogen faster than sprinters?

Answer 18

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

Question 19

In endurance type activities what should you want the muscles to use?

Answer 19

want to use fat and spare glycogen
-training and diet may help

Question 20

What may help prevent carbohydrate depletion fatigue?

Answer 20

supplementation of carbohydrates during exercise (would lead to using more blood glucose which could spare muscle glycogen)

Question 21

When is carbohydrate depletion not likely?

Answer 21

during most activities relying on anaerobic ATP synthesis (duration is too short)

Question 22

When could carbohydrate depletion occur during short activities?

Answer 22

if muscle glycogen stores are low to begin with
Ex: 3 day eventing

Question 23

Dehyrdration

Answer 23

result of fluid loss associated with sweating
-plasma volume decreases which decreases oxygen transport

Question 24

Heat accumulation

Answer 24

-can effect muscle function
-can effect central nervous system function

Question 25

Electrolyte imbalances

Answer 25

defects/disturbances in nerve and muscle function

Question 26

Other causes of fatigue include:

Answer 26

-dehydration
-heat accumulation
-electrolyte imbalances
All interwoven with each other