Exercise/Sports Physiology

Dr. shafali singh

Learning objectives

■ CARDIOVASCULAR RESPONSES ■ RESPIRATORY RESPONSES

■ Physical Training and Conditioning

• The cardiovascular adjustments that occur during exercise consist of a combination of neural and local (chemical) factors.

Neural factors include • (1) central command, • (2) reflexes that originate in the contracting

muscle, and • (3) the baroreceptor reflex

Mild to Moderate Exercise

• Anticipation of physical activity inhibits vagal nerve impulses to the heart and increases sympathetic discharge.

• The result is an increase in heart rate and myocardial contractility which increase cardiac output.

Cardiac Output

• Increased because of increased heart rate.• If the workload increases, the heart rate

increases concomitantly until a plateau of about 180 beats/min is reached during strenuous exercise.

• In contrast to the large increase in heart rate, the increase in stroke volume is only about 10% to 35%, the larger values occurring in trained individual.

Olympic athletes who run marathons or perform cross countryskiing have much higher maximum cardiac outputs than non-

athletes. Which of the following statements about the hearts of these athletes compared to non-athletes is most accurate?

A) Stroke volume in the Olympic athletes is about 5% greater at rest

B) Percentage increase in heart rate during maximal exercise is much greater in the Olympic athletes

C) Maximum cardiac output is only 3% to 4% greater in the Olympic athletes

D) Resting heart rate in the Olympic athletes is significantlyhigher

Approximate distribution of cardiac output at rest and at different levels of exercise up to the maximal O2 consumption ((VO2max) in a normal young man

VO2 max – maximal O2 consumption

• The level (point) where further increase of workload does not bring about further increase in VO2 .

• The VO2 max of an individual determines the maximal aerobic work capacity;

• Contracting muscle avidly extracts O2 from the perfusing blood and thereby increases the arteriovenous O2 difference .

• This release of O2 from blood is facilitated by the shift in the oxyhemoglobin dissociation curve during exercise.

• Oxygen consumption may increase as much as 60-fold, with only a 15-fold increase in muscle blood flow.

• Muscle myoglobin may serve as a limited O2 store during exercise, and it can release the attached O2 at very low partial pressures. However, myoglobin can also facilitate O2 transport from capillaries to mitochondria by serving as an O2 carrier

Venous Return

• sympathetically mediated constriction of the capacitance vessels in both exercising and non exercising parts of the body,

• pumping action of the working skeletal muscles and the muscles of respiration

Peripheral resistance

• Sympathetic-mediated vasoconstriction increases vascular resistance and thereby diverts blood away from the skin, kidneys, splanchnic regions, and inactive muscle.

• The local accumulation of metabolites relaxes the terminal arterioles, and blood flow through the muscle may increase 15- to 20-fold above the resting level. This metabolic vasodilation of the precapillary vessels in active muscles occurs very soon after the onset of exercise.

• Overall there is a decrease in TPR

Blood pressure

• Mean blood pressure increases only slightly because, the effect of enhanced cardiac output is offset by an overall decrease in TPR

• The actual mean arterial pressure attained during exercise represents a balance between cardiac output and TPR

• Systolic pressure usually increases more than diastolic pressure, which results in an increase in pulse pressure . The larger pulse pressure is primarily attributable to a greater stroke volume

Blood pressure1. In systemic circulationa) Systolic blood pressure:Increase in linearity with severity of exercise.b) Diastolic blood pressure:No change in mild to moderate exercise( total resistance falls considerably due to drastic vasodil in working muscle)

Slight increase in severe exercise( due to vasoconstriction in non working muscles and skin)

c)Mean blood pressure increases during heavy exercise

Severe Exercise

• The compensatory mechanisms begin to fail. The heart rate attains a maximal level of about 180 beats/min, and stroke volume reaches a plateau.

• Sympathetic vasoconstrictor activity supersedes the vasodilator influence on vessels of the skin such that the rate of heat loss is decreased.

• A reduction in heat loss through cutaneous vasoconstriction can lead to very high body temperatures and to acute distress during severe exercise.

• Tissue pH and blood pH decrease as a result of increased lactic acid and CO2 production. The reduced pH may be a key factor that determines the maximal amount of exercise that a given individual can tolerate.

• Muscle pain, a subjective feeling of exhaustion, and loss of the will to continue determine exercise tolerance

Post exercise Recovery

• Reduced cardiac output• Persistence of vasodilation in the muscles• Therefore arterial pressure falls, often below

pre exercise levels, for brief periods. • Blood pressure is then stabilized at normal

levels by the baroreceptor reflexes

Limits of Exercise Performance

• The two main factors that limit skeletal muscle performance in humans are the rate of O2 utilization by the muscles and the O2 supply to the muscles

Physical Training and Conditioning

• Training progressively increases Vo2max, which reaches a plateau at the highest level of conditioning.

• greater stroke volume, and lower peripheral resistance

• Low resting heart rate -is caused by a higher vagal tone and a lower sympathetic tone.

• Greater extraction of O2 from the blood (greater arteriovenous O2 difference) by the muscles.

• Capillary density in skeletal muscle increases.. • The number of mitochondria increases, as do

the oxidative enzymes in mitochondria. In addition, levels of ATPase activity, myoglobin, and enzymes involved in lipid metabolism increase in response to physical conditioning

• Which of the following parameters is decreased during moderate exercise?

(A) Arteriovenous O2 difference

(B) Heart rate(C) Cardiac output(D) Pulse pressure(E) Total peripheral resistance (TPR)

Respiratory changes

1.Pulmonary ventilation due to

1.Cortical stimulation2. Increase in body temperature3.Increased catecholamines level4.Increased PCO2 level

5.Increased impulses to ARAS

• In exercise, there is increased ventilation and pulmonary blood flow. The ideal VA/Q is no longer 0.8; it is greater than 0.8.

• Thus, during exercise, ventilation increases more than cardiac output. Also, the base–apex flows are more uniform.

2. O2 usage/consumption

More exercise More O2 usage

1. in PV2. in O2 uptake in lungs

3. in blood flow to tissues4. in PO2 & PCO2 in tissues

Measuring Maximal Oxygen Uptake Is the most Common Method of Quantifying Dynamic Exercise

Which of the following statements about respiration inexercise is most accurate?A) Maximum oxygen consumption of a male marathonrunner is less than that of an untrained average maleB) Maximum oxygen consumption can be increasedabout 100% by trainingC) Maximum oxygen diffusing capacity of a male

marathon runner is much greater than that of anuntrained average maleD) Blood levels of oxygen and carbon dioxide are

abnormal during exercise

Which of the following sources can produce the greatest amount of ATP per minute over a short period of time?A) Aerobic systemB) Phosphagen systemC) Glycogen-lactic acid systemD) Phosphocreatine systemE) Stored ATP

Which of the following athletes is able to exercise the longest before exhaustion occurs?A) One on a high-fat dietB) One on a high-carbohydrate dietC) One on a mixed carbohydrate–fat dietD) One on a high-protein dietE) One on a mixed protein–fat diet

Most of the energy for strenuous exercise that lasts for more than 5 to 10 seconds but less than 1 to 2 minutes comes from which of the following sources?A) Adenosine triphosphate (ATP)B) Anaerobic glycolysisC) Oxidation of carbohydratesD) Oxidation of lactic acidE) Conversion of lactic acid into pyruvic acid