Exercise Exercise PhysiologyPhysiology

CHAPTER 84

EXERCISE Is the period of enhanced energy expenditureThis energy is provided by increased fuel consumption which is reflected as increased O2 consumption and increased CO2 production

Increased O2 delivery to the tissues and increased removal of

CO2from the tissues is achieved by

cardiovascular responses to exercise respiratory responses to exercise changes at tissue level during

exercise

Types of ExerciseTypes of Exercise

SStatictatic exercise exercise = constant muscle length and increased tension

Dynamic exerciseDynamic exercise = rhythmic cycles of contraction and relaxation; change in muscle length

Types of ExerciseTypes of Exercise

Anaerobic Anaerobic exerciseexercise weight-lifting) – short duration, great intensity (fast-twitch muscle fibers); creatine phosphate + glycogen (glucose) from muscleo2

Aerobic exerciseAerobic exercise running, swimming)- prolonged but at lower intensity (slow-twitch mucle fibers) fuels stored in muscle, adipose tissue and liver (glucose – early, FFA – later) o2

Oxygen consumption during exercise

The increase in ventilation during exercise prevents large changes in the partial pressure of O2 or CO2.

The increase in ventilation occurs before there is a change in blood chemicals.Neuronal signals are sent to the respiratory center during exercise, possibly at the same time signals are being sent to the skeletal muscles.

O2 Consumption and Ventilation During Exercise

OXYGEN CONSUMPTION (VO2) AT REST = 250 ml and increases with severity of exerciseMAXIMAL OXYGEN CONSUMPTION (VO2 MAX)= level of O2 consumption beyond which no further increase in O2 consumption occurs with further increase in severity of exercise

VO2 MAX

Average VO2 max in

adults=3L/min trained athletes=5L/min So VO2 max represents the max

attainable rate of aerobic metabolism during performance of rhythmic muscular work that exhausts the subject in 5-10 minutes

Alveolar Ventilation and Arterial PCO2 During Exercise

The decrease PCO2 at the onset of exercise demonstrates that increasing blood CO2 does not trigger the increase in ventilation during exercise.However, chemical changes do fine-tune the ventilation rate. Notice the decrease in ventilation associated with the decrease in PCO2 at the onset of exercise.

O2 deficit and o2 debt

Period of muscular exercise can be divided into 3 phasesAdaptation phaseSteady phaseRecovery phase

Adaption phaseFirst 2-4 min after beginning exerciseO2 consumption reaches VO2 maxVO2 max is less than O2 demand….O2 deficit developsAnaerobic respiration begins

Steady phasePlateau phase of work done and O2 consumptionAnaerobic respiration continuesBuilt up of lactic acid which is buffered by bicarbonate buffer system

H+ + HCO3-……..H2CO3….H2o + CO2Extra CO2 evolved is removed by hyperventilation

Recovery phase

After cessation of exercise extra amount of O2 is consumed called oxygen debtOxygen debt is proportional to extent to which oxygen deficit occurred during exercise

Significance of oxygen debt

To remove excess lactate accumulatedTo replenish the ATPTo replace myoglobin O2

Muscle fatigueMuscle fatigue

Lactic acid↓ATP (accumulation of ADP and Pi, and reduction of creatine phosphate) ↓ Ca++ pumping and release to and from SR↓ ccontraction and relaxationIonic imbalances muscle cell is less responsive to motor neuron stimulation

↓ the rate of ATP hydrolysis, ↓ efficiency of glycolytic enzymes, ↓Ca2+ binding to troponin, ↓ interaction between actin and myosin (muscle fatigue)during rest is converted back to pyruvic acid and oxidized by skeletal muscle, or converted into glucose (in the liver)

How does the respiratory How does the respiratory system respond to system respond to

exercise?exercise?

Major factors which stimulate Major factors which stimulate increased ventilation during exercise increased ventilation during exercise

include:include:neural input from the motor areas of the cerebral cortexproprioceptors in the muscles and joints body temperaturecirculating NE and E pH changes due to lactic acid

Rest Exercise intensity V02maxArterial blood

pH

Before expected exercise begins, Before expected exercise begins,

ventilation ventilation risesrises

emotional hyperventilation‘at any rate, impulses descending from the cerebral cortex are responsible

During the exercise, During the exercise, stimuli stimuli from the from the muscles, joints and muscles, joints and perhaps such sensory perhaps such sensory receptors as pressure receptors as pressure endings in the feet, endings in the feet, contribute to the contribute to the elevation of elevation of ventilationventilationso do chemicals, originating in the active muscles.

Increase oxygen uptake by lungs

Increases from 250ml at rest to 4L/minThis is achieved by

*increased ventilation * increased alveolar capillary PO2 * increased pulmonary diffusion capacity

Changes at the tissue level

Increased blood flow to the exercising musclesIncreased PO2 gradient between the systemic capillaries and tissuesRightward shift of oxygen Hb dissociation curve (increased 2,3DPG and temperature)

How does the How does the cardiovascular system cardiovascular system respond to exercise?respond to exercise?

Cardiovascular responses to exercise

Increase in cardiac output (COP)Increase in heart rateIncrease in blood pressureIncrease in skeletal muscle blood flowChanges in blood volume

Increased CO can be achieved by raising either stroke volume (SV) or heart rate (HR)steady-state HR rises essentially linearly with work rate over the whole range from rest to VO2max :increased sympathetic and decreased parasympathetic discharge to the cardiac pacemaker + catecholaminesreflex signals from the active muscles blood-borne metabolites from these muscles temperature rise

CCardiac output (COp)ardiac output (COp) increaseincrease

Venousreturn

Skin andsplanchnic blood

volume

Maintenance ofventricular fillingMuscle

“pump”

Cardiacoutput

Cardiaccontractility

HR

ExerciseExercise ↑ Muscle pump + ↑ symp. vasocon. ↑ Muscle pump + ↑ symp. vasocon. ↑ Venous ↑ Venous returnreturn ↑ ↑ stroke volumestroke volume ↑ ↑ cardiac outputcardiac output

Blood Blood PPressure ressure (BP) (BP) also rises in also rises in

exerciseexercise systolic pressure (SBP) goes up to 150-170 mm Hg diastolic scarcely alters in isometricisometric (heavy static) exercise, SBP may exceed 250 mmHg, and diastolic (DBP) can itself reach 180

cardiovascular adaptations to cardiovascular adaptations to eexercise trainingxercise training

Adaptations that increase muscle oxidative capacity and delay lactate production ↓↓ muscle chemoreflexmuscle chemoreflex influence on cardiovascular systemAs a result sympathetic activity is decreased, which lowers BP and HR (trained people)

Increase in skeletal muscle blood flow

It is 2-4ml/100gm/min of muscle tissueIncreases 20 times i.e.50-80 ml/100gm/minAchieved by

* arteriolar dilatation * opening up of dormant capillaries

Redistribution of blood flow

Hormonal responses Hormonal responses during exerciseduring exercise

During exerciseDuring exerciseNorepinephrine rises again ('fight or flight'). Increases glycogen breakdown and elevates free fatty acids; also cardiovascular effects as in anticipatory phase

Glucagon rises (to keep up blood sugar). Increases glucose release from liver

Cortisol rises (response to the stress). Increases use of fatty acids, reinforces glucose elevation

Growth hormone begins to rise (damage repair). Stimulates tissue repair, enhances fat use instead of glucose

ADH is released in considerable quantities. It's not just socially inconvenient to have to urinate during exercise - it's a waste of fluid which will probably be needed as sweat. Testosterone/estrogen increase with exercise - probably, over many repetitions, promoting increased muscle bulk Aldosterone also rises, reducing Na+ loss in sweat (and in such urine as is still produced).