Exercise Physiology Flashcards
What is a measure of O2 consumption and thus athletic ability of an animal?
VO2 max
-measure of aerobic metabolism
How does VO2 max in an horse compare to catte?
VO2 max is 2.5x that of cattle
The mass of the horses heart is __________% body weight
0.9-1
Muscle accounts for ___% of body weight of equine
50
How can the horse increase O2 delivery to muscles under extreme exercise ?
increase HR —> increase O2 carrying capacity
Increase RBC numbers to PCV (splenocontraction)
Can reach greater O2 extraction than other species
What are the three major pathways for energy supply to muscles? What are the substrate?
Phosphocreatine
Anaerobic glycolysis - glucose / glycogen
Aerobic - carbohydrates (glycogen and glucose) and free fatty acids
T/F: horses have higher concentration of intramuscular glycogen and number of mitochondria/ unit muscle
True
In the first few seconds of exercise, what is the predominant pathway supplying energy?
Phosphocreatinine —> generates a lot of ATP but only for a short time, allows anaerobic pathway to catch up
What is the predominant pathway supplying energy during the first minute of exercise and during maximal exercise?
Anaerobic glycolysis
Process is limited by supply of glycogen in muscle and build up of lactic acidosis
What energy pathway is predominant in submaximal exercise and can be sustained for prolonged periods of time?
Aerobic
How are FFA used for energy??
Undergo beta oxidation - oxidative phosphorylation
—> makes 3x more ATP
Requires more oxygen and production is slow
What is the recruitment of energy systems??
Initially use stored ATP
At low intensity exercise, mostly aerobic metabolism
- > glycogen stores used until 20-30% used, then switch to fat as a substrate
- > FFA oxidation is highest at 40-60% VO2 max
- > glycogen stores used at >60%VO2 max
High intensity
- > use circulating glucose and glycogen stores
- > energy increases that cannot be met by oxygen, are supplanted with anaerobic
What are the muscle fiber types present in horses?
Type I
Type IIA
Type IIX
Type I and IIa
Type IIAX
What are the characteristics of a type I muscle fiber?
Slow hydrolysis of ATP
Low glycogen content
High number of capillaries
High oxidative capacity
Not powerful
Fatigue slowly
The forelimb has predominantly type ____ muscle fibers
I
Sustain isometric force
What are characteristics of type IIA muscle fibers?
Generate force rapidly
Large number of capillaries and mitochondria
Glycolytic and oxidative mechanisms
Sustain high power for prolonged periods
What are characteristics of type IIX muscle fibers ?
2x faster than IIA
High power but limited duration
Large cross sectional area, low capillaries
What type of fibers are only recruited near maximal intensity (sprinting/jumping) and during extremely prolonged submaximal exercise ?
Type IIX
What is the order of fatigue seen in muscle fibers during aerobic metabolism
Type I > type IIA > typeX
T/F: Splenocontraction increases oxygen carrying capacity by increasing circulating RBC volume and increases stroke volume
True
By how much can CO change in a horse doing extreme exercise ?
Increase from 25L/min to about 300L/min
T/F: maximum heart rate is age dependent
True
Performance tends to be better in younger horses
How is stroke volume increased during exercise?
Splenocontraction
Venous return enhanced by vasoconstriction, muscle contraction, and intrathoracic pressure changes
Improved myocardial contractility-> SNS
During exercise, carotid pressures can increased from 120mmHg to 220mmHg, but the MAP does not increase by much, how??
Lowering of the peripheral vascular resistance by vasodilation of the muscular and cutaneous capillary beds
How is the minute ventilation increased during exercise in the horse??
Increase RR and tidal volume
How can tidal volume be increased in the horse?
Increased diaphragm contractions and intrapleural pressure changes
Increased flow
Visceral content acts as a pump: forelegs move forward and rib change pulled forward and outward
How can resistance to airflow be decreased during exercise?
High resistance in upper airways —> controlled by extension of head and of musculature results in stabilization of muscles of upper airway
Cartilaginous support opposes forces of collapse associated high negative pressure
How can O2 extraction be increased during exercise?
Low tissue O2 increases concentration gradient, favoring off-loading
Right shift dissociation curve
- > hypercarbia
- > high temperature
- > tissue acidosis
What are the limitations to increasing HR and blood flow during exercise??
Excessive HR—> decreased ventricular filling
Excessive flow —> decreased transit time in capillary doesnt allow for full saturation (Decreased oxygen uptake —> hypoxemia)
At canter and gallop stride frequency, RR rate is coupled at a ______ ratio
1:1
Training results in what adaptations of the CVS system?
Lower HR at submaximal exercise
Increased heart mass
Increases in RBC volume, Hb concentration, PV, SV muscle contraction
Training results in what adaptations of the musculature?
Change in fibers, hypertrophy
IIX —> IIXA —> IIA —> I and IIA —> I
Change in enzymatic systems: increased aerobic metabolism, change mitochondria and capillary density
Modest increase in glycogen reserve
