Exercise Physiology

Question 1

What is a measure of O2 consumption and thus athletic ability of an animal?

Answer 1

VO2 max

-measure of aerobic metabolism

Question 2

How does VO2 max in an horse compare to catte?

Answer 2

VO2 max is 2.5x that of cattle

Question 3

The mass of the horses heart is __________% body weight

Answer 3

0.9-1

Question 4

Muscle accounts for ___% of body weight of equine

Answer 4

50

Question 5

How can the horse increase O2 delivery to muscles under extreme exercise ?

Answer 5

increase HR —> increase O2 carrying capacity

Increase RBC numbers to PCV (splenocontraction)

Can reach greater O2 extraction than other species

Question 6

What are the three major pathways for energy supply to muscles? What are the substrate?

Answer 6

Phosphocreatine

Anaerobic glycolysis - glucose / glycogen

Aerobic - carbohydrates (glycogen and glucose) and free fatty acids

Question 7

T/F: horses have higher concentration of intramuscular glycogen and number of mitochondria/ unit muscle

Answer 7

True

Question 8

In the first few seconds of exercise, what is the predominant pathway supplying energy?

Answer 8

Phosphocreatinine —> generates a lot of ATP but only for a short time, allows anaerobic pathway to catch up

Question 9

What is the predominant pathway supplying energy during the first minute of exercise and during maximal exercise?

Answer 9

Anaerobic glycolysis

Process is limited by supply of glycogen in muscle and build up of lactic acidosis

Question 10

What energy pathway is predominant in submaximal exercise and can be sustained for prolonged periods of time?

Answer 10

Aerobic

Question 11

How are FFA used for energy??

Answer 11

Undergo beta oxidation - oxidative phosphorylation

—> makes 3x more ATP

Requires more oxygen and production is slow

Question 12

What is the recruitment of energy systems??

Answer 12

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

Question 13

What are the muscle fiber types present in horses?

Answer 13

Type I
Type IIA
Type IIX

Type I and IIa
Type IIAX

Question 14

What are the characteristics of a type I muscle fiber?

Answer 14

Slow hydrolysis of ATP

Low glycogen content
High number of capillaries
High oxidative capacity

Not powerful
Fatigue slowly

Question 15

The forelimb has predominantly type ____ muscle fibers

Answer 15

I

Sustain isometric force

Question 16

What are characteristics of type IIA muscle fibers?

Answer 16

Generate force rapidly
Large number of capillaries and mitochondria
Glycolytic and oxidative mechanisms
Sustain high power for prolonged periods

Question 17

What are characteristics of type IIX muscle fibers ?

Answer 17

2x faster than IIA
High power but limited duration

Large cross sectional area, low capillaries

Question 18

What type of fibers are only recruited near maximal intensity (sprinting/jumping) and during extremely prolonged submaximal exercise ?

Answer 18

Type IIX

Question 19

What is the order of fatigue seen in muscle fibers during aerobic metabolism

Answer 19

Type I > type IIA > typeX

Question 20

T/F: Splenocontraction increases oxygen carrying capacity by increasing circulating RBC volume and increases stroke volume

Answer 20

True

Question 21

By how much can CO change in a horse doing extreme exercise ?

Answer 21

Increase from 25L/min to about 300L/min

Question 22

T/F: maximum heart rate is age dependent

Answer 22

True

Performance tends to be better in younger horses

Question 23

How is stroke volume increased during exercise?

Answer 23

Splenocontraction

Venous return enhanced by vasoconstriction, muscle contraction, and intrathoracic pressure changes

Improved myocardial contractility-> SNS

Question 24

During exercise, carotid pressures can increased from 120mmHg to 220mmHg, but the MAP does not increase by much, how??

Answer 24

Lowering of the peripheral vascular resistance by vasodilation of the muscular and cutaneous capillary beds

Question 25

How is the minute ventilation increased during exercise in the horse??

Answer 25

Increase RR and tidal volume

Question 26

How can tidal volume be increased in the horse?

Answer 26

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

Question 27

How can resistance to airflow be decreased during exercise?

Answer 27

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

Question 28

How can O2 extraction be increased during exercise?

Answer 28

Low tissue O2 increases concentration gradient, favoring off-loading

Right shift dissociation curve

• > hypercarbia
• > high temperature
• > tissue acidosis

Question 29

What are the limitations to increasing HR and blood flow during exercise??

Answer 29

Excessive HR—> decreased ventricular filling
Excessive flow —> decreased transit time in capillary doesnt allow for full saturation (Decreased oxygen uptake —> hypoxemia)

Question 30

At canter and gallop stride frequency, RR rate is coupled at a ______ ratio

Answer 30

1:1

Question 31

Training results in what adaptations of the CVS system?

Answer 31

Lower HR at submaximal exercise
Increased heart mass

Increases in RBC volume, Hb concentration, PV, SV muscle contraction

Question 32

Training results in what adaptations of the musculature?

Answer 32

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