Exercise Phys Unit 3

Fatigue

Decrements in muscular performance with continued effort accompanied by general sensations of tiredness or inability to maintain the required power output to continue muscular work at a given intensity. Reversible with rest

Peripheral fatigue

Occurs in the muscle itself, alterations of motor nerve control

• A decreased rate of energy delivery (ATP-PCr, anaerobic glycolysis, and oxidative metabolism)

• Accumulation of metabolic by-products, such as lactate and hydrogen and phosphate

• Failure of the muscle fiber’s contractile mechanism ( decreased ACh/stim threshold, decreased receptor activation)

Central fatigue

Changes in the brain or central nervous system

• Alterations in neutral control of muscle contraction

Accumulation of Pi by-product

The breakdown of ATP during PCR leaves high level of pi

• May be the largest contributor to fatigue

• Impairs contractile function of myofibril

• Reduce calcium release from the sarcoplasm reticulum

• An increase in both pi and ADP also inhibit ATP breakdown through negative feedback

Accumulation of H+

H+ accumulation from lactate causes muscle acidosis (decreased pH)

• PH changed can affect energy production and muscle contraction

• A low intracellular pH inhibits phosphofructokinase ph < 6.9

• Or stops glycogen breakdown reducing ATP

• Also may lower the amount of calcium released

Neuralmuscular control theory

muscle cramps occur when control between the motor neurons and muscles become altered.

• A muscle fatigue develops, excitation of the muscle spindle and inhibition of the golgi tendon organ occurs resulting in abnormal a-motor neuron activity and reduced inhibitory feedback

• . Abnormal repeated firing motor units makes the muscle cramps

Electrolyte depletion theory

Occurs in athletes who have been sweating excessively with electrolyte imbalance.

• Progressive dehydration and electrolyte depletion cause fluid to shift from the interstitial compartment to the intravascula compartment

• This contracts the extracellular fluid compartment increasing surrounding neurotransmitter concentrations and causing selected motor nerve terminals to become hyperexcitable, leading to spontaneous discharge, Initiation of action potentials in the muscles and ultimately muscle cramps

Normal heart beat

60-100 beats/minute

bradycardia

RHR lower than 60 beats/min

Tachycardia

RHR greater than 100 beats/min

Ventricular fibrillation

Depolarization of the ventricular tissue is random and uncoordinated

Stroke volume

• 60 ml of blood

• The volume of blood pumped during one beat (contraction)

• Difference of EDV and ESV

• Someone who is trained has a larger stroke volume

Cardiac output (Q)

Total volume of blood pumped by the ventricle per minute, the product of heart rate and SV. 5 L/minute

End diastolic volume (EDV)

At the end of diastole, just before contraction, the ventricle has finished filling. The volume of blood it now contains is this. At rest healthy adult approximately 100 ml

End Systolic Volume (ESV)

At the end of systole just after contraction, value is approximately 40 ml. At the end of systole just after contraction, the ventricle has completed its ejection phase, but not all the blood is pumped out of the heart. The volume of blood rematining is this

Ejection fraction

• The fraction of the blood pumped out of the left ventricle in relation to the amount of blood that was in the ventricle before contraction. Dividing Sv by EDV Above 60% is healthy

• 60% of blood in the ventricle at the end of diastole is ejected with next contraction and 40% remains

What is a normal systolic blood pressure (SBP) and diastolic blood pressure (DBP)?

Normal blood pressure for adults is generally defined as a systolic pressure (top number) of less than 120 mmHg and a diastolic pressure (bottom number) of less than 80 mmHg.

MAP

MAP = ⅔ DBP + ⅓ SBP

12. In which blood vessels does MOST peripheral RESISTANCE occur as blood circulates?

Arterioles

Extrinsic neural control in blood flow distribution

• Increase in sympathetic activity → increase in vasoconstriction

• Decrease sympathetic activity → decrease in vasoconstriction

Blood flow at rest

Distributed among the vasculature, digestion tract, and skin

Cardiac output is 5 L/minute

Blood flow during exercise

During exercise blood goes away from the inactive organ and into heart and muscles

Cardiac output is 25 L/miute

How much blood does the average man/woman have in their entire body

5-6 Liter in men and 4-5 Liters in women

normal hematocrit

Men: 41-50%

Women: 46%-44% for adult women

With a normal hematocrit how much oxygen can the average person carry per 100 ml blood?

20 ml of O2 per 100 ml of blood

Pulmonary ventilation

external respiration; breathing in and out of the lungs

Pulmonary diffusion

External respiration; O2 and Co2 exchange between alveoli and blood

Capillary diffusion

Gas exchange between blood and tissuesO2 going out and CO2 going in

tidal volume

Average tidal volume is about ½-1L per breath. Is the amount of air entering and leaving the lungs with each normal breath

vital capacity

 3-5 L is the greatest amount of air that can be expired after a maximal inspiration

residual volume

1-2 L is the amount of air remaining in the lungs after maximal expiration

total lung capacity

5-8 L Is the sum of vital capacity and residual volume

Normal breathing rate

10-12 breaths/minutes, 5-10 L/minute at rest

Partial pressure

• O2 moves alveoli →blood →tissues 

• CO2 moves tissues →blood → lungs

Henry’s law

Amounts of gas dissolved in liquid depends on partial pressure + solubility

Boyle’s law

↑ volume → ↓ pressure → air enters

↓ volume → ↑ pressure → air leaves

Dalton’s law

Total pressure = sum of the parts

Fick’s law

The bigger of difference in pressures the bigger in gas exchange

Minute ventilation (VE)

Tidal volume (TV) x breathing frequency (f)

Factors that influence oxygen saturation levels during exercise

• ↑ temperature

• ↑ CO₂

• ↓ pH

• ↓ pO₂

(a-v)O2 difference

At rest: Small difference capillaries takes about 4-5 ml during rest

During exercise: Big increase. capillaries Takes about 15 ml O2 during exercise

factors that regulate pulmonary ventilation

• Mechanoreceptors in the muscles (first stimulus)

• PCO2 (most important): As it increases → increases breathing

• pH: Decreases (more acidic) →increases breathing

Temperature: Increases →increases breathing (exercise/fever)