Fatigue

Question 1

Two common causes of muscle fatigue

Answer 1

1. Substrate depletion (primarily carbohydrates)

2. End product accumulation (primarily lactic acid)

Question 2

What sport has the highest rate of muscle glycogen use?

Answer 2

Galloping near racing speed

Question 3

What sport has the quickest depletion of muscle glycogen?

Answer 3

100 mile endurance ride

Question 4

Depletion of muscle glycogen during various activities

Answer 4

• Endurance horses are more likely to deplete their muscle glycogen than QH and TB sprinters
• Sprinters use glycogen at a higher rate but for short time
• Endurane horses use glycogen at slow rate but for many hours

Question 5

What nutrient depletion can cause fatigue for endurance racers?

Answer 5

Carbs

-supplementation during exercise is important and may help

Question 6

Carbohydrate depletion is not likely during most activities UNLESS…

Answer 6

Muscle glycogen sores are low at onset

ex: 3 day eventing, levels might not be 100% after cross country day; horses aren’t best at replacing

Question 7

Lactic Acid break down

Answer 7

lactate + hydrogen ion (H+)

Question 8

End product accumulation

Answer 8

Lactic acid

• byproduct of metabolism
• produced when oxygen availability is limiting
• produced by fast twitch fibers even when oxygen is not limiting

Question 9

Lactic acid and exercise intensity relationship

Answer 9

Increase exercise intensity increases type IIX fiber recruitment, increases lactic acid production

Question 10

Anaerobic metabolism and VO2 max

Answer 10

Anaerobic metabolism will allow the horse to work beyond VO2 max, just not for very long

Question 11

Order of lactic acid accumulation by activity from LEAST TO GREATEST

Answer 11

Endurance, show jumping, eventing, harness racing, TB racing

Question 12

What happens if bicarbonate is depleted?

Answer 12

There will be no way to make carbonic acid and H+ will build up with will lower the body’s pH

Question 13

Lactic acid metabolism

Answer 13

H+ + HCO3 = H2CO3 => H2O & CO2 => Breathe out

Question 14

Other cases of fatigue

Answer 14

1. Heat accumulation (dehydration, redistribute blood from muscles to skin
2. Electrolyte imbalances (fluid balance, acid base balance, neural activity, muscle activity)

Question 15

Horses sweat

Answer 15

-hypertonic: more electrolytes in sweat than plasma

Question 16

Effects of training

Answer 16

• minimal effects on respiratory system
• Some effects on cardiovascular
  1. max HR not changed
  2. SV may increase
  3. Increased capillary density in muscles
  4. Increased oxidative and aerobic capacity

Question 17

Effects of training on muscle

Answer 17

Change in metabolic characteristics

1. increase in muscle glycogen concentrations
2. increase in intracellular buffering
3. increase in aerobic metabolism

Question 18

Who uses O2 more efficiently?

Answer 18

Trained horses

Question 19

Which horse uses less glycogen?

Answer 19

Trained horses

Question 20

Which horses has the higher VO2 max?

Answer 20

Trained horses

Question 21

Which horses produces less lactate at a given intensity?

Answer 21

Trained horses