Exercise Physiology Flashcards
What needs to happen for muscles to perform?
Adequate energy and oxygen supply to the muscles
Incorporates CVS, respiratory, locomotor, and endocrine systems as well as nutrition
What kind of races do thoroughbred and quarter horses run?
Thoroughbred- Marathon
Quarter- sprints
How best is athletic ability evaluated?
By VO2max (oxygen consumption)
What is the oxygen consumption of a fit racehorse?
160 mL/kg/min
2x that of elite humans and 2.6x cattle
Why do horses tend to have a higher hematocrit?
Splenic reserve volume allowing for rapid changes when necessary (prey animal)
How are the lungs adapted for exercise?
They’re really big
2x that of cattle with 1.6x the surface area for maximal gas exchange
What is the typical heart mass of a horse?
0.9-1% of BW in kg
Large compared to other athletic species
Secretariat was 2%
T/F: Max HR is similar to cattle but horses have greater CO and SV.
True
Normal rates are 25-44 and can get up to 220-250 at the end of a race
What percentage of body weight does a horse’s muscle mass comprise?
~50%
T/F: Horses have lower intramuscular glycogen stores than other animals.
False- they have higher ~140mmol/kg
T/F: Horses have higher number of mitochondria per unit of muscle weight.
True- approx 2x that of cattle
What are the three energy pathways for muscle?
- Creatine phosphate
- Anaerobic glycolysis
- Aerobic glycolysis and fat oxidation
What is the creatine phosphate pathway?
Generation of a ton of ATP that is only sustained for
How does anaerobic glycolysis work?
Glucose breakdown into lactate and ATP
Rapid process that produces enough energy to sustain for ~1min by itself before aerobic pathway kicks in
Why does anaerobic glycolysis occur?
In the cytoplasm
What is anaerobic glycolysis limited by?
The supply of glycogen in the muscle
When does the aerobic pathway become the primary pathway for energy creation?
After ~2min of exercise
Where does the aerobic pathway occur?
In the mitochondria
How long does the aerobic pathway have to be running before it comes to maximal function?
35-40sec
What is the aerobic pathway sustained by?
Continuous oxygen supply- as long as oxygen supply is adequate the aerobic pathway can be sustained for prolonged periods
Where does the aerobic pathway get it’s fuel?
Circulating FFAs from adipose tissues and from muscle stores
How much more ATP does the aerobic pathway created compared to the anaerobic pathway?
3x but the rate of production is slower
Low-intensity exercise primarily uses what pathway?
Aerobic pathway
At what percentage of glycogen depletion does the body switch to fat as an energy substrate?
20-30% depletion
Why is it important to reserve glycogen stores in the horse?
Allows for some substrate to be saved so that you can switch from sub-maximal to high intensity exercise quickly
At what percentage of VO2max is FFA oxidation the highest?
40-60%
What can be used as a substrate at >60% CO2max?
Carbohydrates (glycogen)
As exercise increases and oxygen consumption increases, what pathway may the horse revert back to? Why?
Anaerobic because they are no longer able to maintain the amount of oxygen required for the aerobic pathway to function adequately
Why does training a sprinter for aerobic capacity help them even though they rarely enter the aerobic phase during competition?
May decrease lactic acid production
What determines the proportion of energy derived from each substrate?
- Speed/endurance of the work
- Feed composition
- Fitness level and conditioning
- Muscle fiber composition
- Age
What is the substrate use summary?
- Glucose plays a very small part in the energy produced (10%)
- 60% of fat is used in low-intensity vs. 35% of fat used in high-intensity
- 30% glycogen is used in low-intensity vs. 55% of glycogen used in high-intensity
How many muscle fiber types are there?
3
What are type I muscle fibers?
Slow twitch oxidative fibers
What are some characteristics of type I muscle fibers?
- Hydrolyze ATP slowly
- High number of capillaries
- Slow fatigue
- Slow, repetitive movement
- Poor power generation
Where are type I muscle fibers mostly concentrated?
Stance sustaining muscles of the forelimbs
What are type II muscle fibers?
Fast twitch fibers
Fast cross bridging cycle that generates force rapidly
What are some characteristics of type IIA muscle fibers?
- Large number of capillaries and mitochondria
- Glycolytic and oxidative mechanisms
- Sustain high power for prolonged periods
What are some characteristics of type IIX muscle fibers?
- 3x faster than IIA
- Adapted for high power output limited duration
- Large cross-sectional area low capillaries
Where are type II muscle fibers mostly found?
Hind limbs
What are type IIAX fibers?
Found in locotomor muscles
What type of muscle fibers are used in postural muscles?
Type I
What order are muscle fibers recruited in?
Type I > IIA > IIAX > IIX
When are type IIAX mostly recruited?
Near maximal intensity or during extremely prolonged submaximal exercise
