Exercise Physiology: Hormonal, Muscular, and Cardiovascular Mechanisms

Muscle glycogen breakdown mechanisms

Epinephrine via cAMP pathway, calcium release during contraction, and high AMP levels activate glycogen phosphorylase.

Hormones during exercise

Increase: Epinephrine, Norepinephrine, Glucagon, Cortisol, Growth Hormone. Decrease: Insulin.

Role of Epinephrine & Norepinephrine during exercise

Increases HR, BP, glycogen breakdown, and fat metabolism.

Role of Cortisol during exercise

Increases with intensity; breaks down protein, maintains blood glucose, promotes fat metabolism.

Role of Growth Hormone (GH)

Increases fat metabolism, conserves glucose.

Role of Glucagon during exercise

Promotes liver glycogen breakdown and glucose release.

Role of Insulin during exercise

Decreases during exercise; allows glucose to stay in blood for muscle use.

Plasma glucose maintenance during exercise

1. Liver glycogen breakdown 2. FFA mobilization 3. Gluconeogenesis 4. Reduced glucose uptake (insulin suppression)

Divisions of the Autonomic Nervous System

Sympathetic (fight or flight) increase HR, and BP. Parasympathetic (rest and digest) Decreases HR and promotes recovery.

Function of muscle spindles

Detect muscle length and stretch.

Function of Golgi tendon organs

Detect muscle tension to prevent excessive force.

Motor unit recruitment (size principle)

Small to large motor units are recruited as force demands increase.

Role of Calcium in muscle contraction

Released from SR, binds to troponin, moves tropomyosin, allows actin-myosin binding.

Sliding Filament Theory

Muscle shortens as actin slides over myosin; Ca++ binds to troponin → binding sites exposed → power stroke → contraction.

Types of muscle contraction

Dynamic (concentric/eccentric) and static (isometric).

muscle fiber type 1

slow twitch fibers

- aerobic, use very little ATP

slow speed, generate less tension

- myoglobin gives red color

muscle fiber type 2

hybrid mix, moderate power.

muscle fiber type iix

Fast twitch, anaerobic, High power.

Muscle fiber types and characteristics

Type I: Slow, aerobic, fatigue-resistant. Type IIa: Hybrid, moderate power. Type IIx: Fast, anaerobic, high power.

Function of the myocardium

Cardiac muscle tissue that contracts to pump blood. (middle muscle of heart)

Cardiac contraction phases

Rest = diastole (filling). Exercise = shorter diastole, stronger systole (pumping).

Heart rate regulation

SNS increases HR, PSNS decreases HR

Cardiac variable responses during exercise

↑HR, ↑SV, ↑Q, ↑BP, ↑A-VO2 difference.

Regulation of stroke volume

Frank-Starling mechanism, contractility, venous return.

Fick Equation

VO₂ = Q × (a-vO₂ difference).

Muscles of inspiration

Diaphragm, external intercostals.

Muscles of expiration

Internal intercostals, abdominals.

Pulmonary volumes

TV (tidal), IRV, ERV, RV, TLC, VC.

Function of myoglobin

Transports oxygen within muscle fibers.

Bicarbonate Buffer System equation and purpose

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; maintains blood pH balance.

Activities that affect acid-base balance

High-intensity = greater acid accumulation; low-intensity = minimal disturbance.

Force-Velocity relationship

Concentric: high velocity → low force. Eccentric: low velocity → high force.

Sarcolemma - function

Muscle cell membrane that conducts electrical signals.

Sarcoplasmic Reticulum (SR) - role?

Stores and releases calcium for muscle contraction.

Transverse tubules - role?

Carry electrical impulses deep into the muscle fiber.

Satellite cells - role?

Aid in muscle repair and growth.

Myofibrils - what are they?

Bundles of contractile filaments (actin and myosin) inside muscle fibers.

Sarcomere - function?

The basic contractile unit of muscle.

Actin vs. Myosin?

Actin = thin filament; Myosin = thick filament.

Troponin - function?

Binds calcium (TnC), actin (TnI), and tropomyosin (TnT) to control contraction.

Tropomyosin - function?

Covers actin binding sites when muscle is relaxed.

Myonuclear domain - meaning?

Volume of cytoplasm controlled by each nucleus in a muscle fiber.

what is the myocardium?

the middle muscular layer of the heart.

what are the two contractile phases of the heart.

systole (contract and pump) and diastole (relax and fill)

stroke volume can plateu in many subjects at a certain percent of vo2 max, what is it?

40 - 60 %

what are the three components of the fick equation?

• Cardiac Output (Q) – the amount of blood the heart pumps per minute.

• Arterial Oxygen Content (CaO₂) – the amount of oxygen carried in the arterial blood.

• Venous Oxygen Content (CvO₂) – the amount of oxygen remaining in the venous blood after tissues have used some.

VO2=Q x (A-V)O2

As i go from rest to exercise how does distribution of cardiac output to the heart change? 

The distribution of cardiac output to the heart increases slightly, but its percentage of total output stays about the same or even decreases slightly.

the formula that uses age predicting max heart rate is called?

Karvonen formula (220 - age)

what factors increase stroke volume.

increased venous return, increase contactility.

what factors decrease stroke volume?

increase afterload.

what factors increase venous return?

skeletal muscle pump, respiratory pump, one way valves, muscle contraction, Veno constriction. 

most important muscles for inspiration. 

diaphragm and external intercostals.

most important muscles for expiration?

internal intercostals and abdominals.

tidal volume (tv)

Amount of air inhaled or exhaled during normal, relaxed breathing.

inspiratory Reserve Volume (IRV)

Extra air you can inhale above a normal breath.

Expiratory Reserve Volume (ERV)

Extra air you can exhale after a normal exhale.

Residual Volume (RV)

Air remaining in lungs after maximal exhalation. Cannot be voluntarily exhaled.

Total Lung Capacity (TLC)

Maximum amount of air the lungs can hold.

Vital Capacity (VC)

Max air you can exhale after a max inhale. (all the air you can move in and out voluntarily.”)

Functional Residual Capacity (FRC)

Air left in lungs after a normal exhale

Inspiratory Capacity (IC)

Max air you can inhale after a normal exhale. (how much you can breathe in above a normal breath.)

most important blood buffer?

Bicarbonate

What is the most common and strongest acid produced by the skeletal muscle during heavy exercise.

lactic acid