KRS 354 -Exam 3 PArt 1

What directly slows heart rate via the parasympathetic nervous system, and how?

Vagus nerve inhibition of the SA node and AV node

What neurotransmitter is released by the parasympathetic nervous system to decrease HR?

Acetylcholine

What directly increases heart rate via the sympathetic nervous system?

Cardiac accelerator nerves stimulating the SA and AV nodes

What neurotransmitters increase HR during sympathetic activation?

Epinephrine and norepinephrine

What is vagal tone?

Continuous parasympathetic influence on the heart that keeps resting HR low

Why do endurance athletes have very low resting HR?

Increased vagal tone and decreased sympathetic activity; efficiently pump blood

What causes the immediate increase in HR at the onset of exercise?

Rapid withdrawal of parasympathetic (vagal) tone

Up to what HR is the increase mainly due to parasympathetic withdrawal?

~100 bpm

What causes HR to increase beyond 100 bpm during exercise?

Increased sympathetic stimulation

How does HR respond to increasing exercise intensity?

Increases linearly until maximal heart rate

Define maximal heart rate (HRmax)

The highest HR achievable during maximal effort to exhaustion

Is HRmax variable day-to-day?

No, it is highly reliable day-to-day

How does HRmax change with aging, by how much?

Decreases ~1 bpm per year starting around age 10–15

What is the primary reason VO₂max declines with age?

Decline in HRmax

Tanaka equation for HRmax

HRmax = 208 − (0.7 × age)

Why is HRmax estimation important?

Used to prescribe exercise intensity and predict VO₂max

Define resting heart rate (RHR)

Number of heart beats per minute at rest

Normal RHR range

~60–80 bpm

What RHR values are seen in elite endurance athletes?

~28–40 bpm

How does RHR change with fitness?

Decreases with improved cardiovascular fitness

How does RHR change with age?

Increases with age

What is the anticipatory response?

Increase in HR before exercise due to epinephrine release

Why should pre-exercise HR not be used as RHR?

It is elevated due to anticipatory response

Define steady-state HR

Plateau HR reached during constant submaximal workload

What does steady-state HR represent?

Optimal HR to meet circulatory demands at a given workload

What does a lower steady-state HR indicate?

Greater cardiovascular efficiency

Between what HR range is HR and VO₂ linearly related?

110–150 bpm

Why is this range important?

Used to estimate VO₂max from submaximal exercise

Define stroke volume

Volume of blood ejected per beat (SV = EDV − ESV)

What is EDV?

End-diastolic volume (volume in ventricle before contraction)

What is ESV?

End-systolic volume (volume remaining after contraction)

Resting SV (untrained)

~50 mL/beat

Max SV (untrained)

~120 mL/beat

Max SV (elite athletes)

~200 mL/beat

How does SV change with exercise intensity?

Increases up to 40–60% VO₂max

When can SV continue increasing beyond 60% VO₂max?

In highly trained athletes

What are the 4 determinants of stroke volume?

Venous return, ventricular distensibility(srtretch), contractility, afterload

Define preload

Amount of ventricular filling (EDV)

Define afterload

Pressure the heart must overcome to eject blood

Define contractility

Strength of ventricular contraction independent of preload

Why is venous return important?

Heart can only pump what it receives

What is the Frank-Starling mechanism?

Increased EDV stretches myocardium → stronger contraction → increased SV

When is Frank-Starling most important?

Low-to-moderate exercise intensity

How does sympathetic stimulation increase SV?

Increases contractility via epinephrine and norepinephrine

When is contractility most important?

High exercise intensities

How does afterload decrease during exercise?

Vasodilation reduces total peripheral resistance

How does decreased afterload affect SV?

Allows greater blood ejection

Why is SV higher in supine vs upright position?

Greater venous return due to reduced blood pooling in legs

How much does SV increase in supine exercise?

~20–40%

How much does SV increase in upright exercise?

Can double from rest to max

Why is the increase smaller in supine?

Already elevated at rest

Define cardiac output

Volume of blood pumped per minute (Q = HR × SV)

Resting Q

~5 L/min

Qmax sedentary

<20 L/min

Qmax elite athletes

≥40 L/min

Why does Q increase during exercise?

To meet increased oxygen demand

What is the major limiting factor of VO₂max?

Cardiac output

Why does HR dominate Q at high intensity?

SV plateaus

What happens to systolic BP during exercise?

Increases proportionally with intensity (up to ~200 mmHg)

What happens to diastolic BP?

Remains constant or decreases slightly (~5–10 mmHg)

What is an abnormal DBP response?

Increase ≥15 mmHg → stop test

Why does DBP decrease?

Vasodilation reduces resistance

What % of Q goes to muscle at rest?

15–20%

What % during maximal exercise?

80–85%

Where is blood reduced?

Splanchnic organs (liver, GI, kidneys)

What causes vasodilation in muscle?

↑ H⁺, ↑ CO₂, ↑ temp, ↓ O₂, muscle contraction

Define cardiovascular drift

Increase in HR and decrease in SV during prolonged steady exercise

What happens to Q?

Remains constant

Why does SV decrease?

Reduced venous return

What causes reduced venous return?

Blood shifts to skin + dehydration

How does sweating affect drift?

Decreases plasma volume → decreases preload

How does HR compensation occur?

HR increases to maintain Q

Define (a-v)O₂ difference

Difference between arterial and venous oxygen content

Typical arterial O₂

~20 mL/dL

Typical venous O₂

~14 mL/dL

How does it change with exercise?

Can triple

Why does it increase?

Greater O₂ extraction by muscles

Define minute ventilation

Total air in/exhaled per min; VE = tidal volume × breathing frequency

How does VE change with exercise?

Increases proportionally with metabolic demand

Low intensity change

Increased tidal volume

High intensity change

Increased breathing frequency

Max VE

~100–200 L/min

Define ventilatory threshold (VT)

Point where VE increases disproportionately to VO₂

Occurs at what % VO₂max?

~55–70%

What causes VT?

Accumulation of H⁺ from lactic acid

Why does VE increase sharply?

Buffering produces CO₂ → stimulates breathing

Normal blood pH

7.4 ± 0.05

Acidosis

pH < 7.4

Alkalosis

pH > 7.4

Main blood buffer

Bicarbonate (HCO₃⁻)

Buffer equation

CO₂ + H₂O ⇄ H₂CO₃ ⇄ H⁺ + HCO₃⁻

What stimulates ventilation increase?

↑ H⁺ and ↑ CO₂

Define muscular strength

Maximum force a muscle or muscle group can generate in a single effort (commonly measured by 1RM)

Define 1RM

The maximum amount of weight that can be lifted one time with proper form

Define muscular endurance

Ability of a muscle to sustain repeated contractions or maintain contraction over time

Define muscular power

Rate of doing work (Power = Force × Velocity)

Why is power different from strength?

Power includes speed of contraction, not just force

Define principle of individuality

Each person responds differently to training due to genetics, age, sex, and training history

Give examples of individuality factors

Fiber type distribution, VO₂max baseline, hormone levels

Define principle of specificity

Training adaptations are specific to the muscles used, intensity, and type of exercise performed