Exercise Physiology

UCA- Gallagher Fall 2025

What are the two control centers?

Nervous System and Endocrine System

Nervous System Speed

Fast: Immediate Reaction

Endocrine System Speed

Slow: to fine-tune communication and response

Feedback Loop Order

Stimulus → Sensor → Control Center(s) → Effector → Response

Sensors

Receptors; security cameras (always watching for change)

What is the most common type of FB loop?

Negative (temp regulation, blood glucose, H12 recovery)

What is the most well-known example of a Positive FB loop?

Childbirth/ labor because you want it to go out, not in.

How does the Nervous System communicate - Somatic?

Voluntary → Skeletal Muscle

How does the Nervous System communicate - Autonomic?

Involuntary → HR, BP

• Sympathetic: Stress Response → fight or flight (think Superman)

• Parasympathetic: Recovery → Rest & Digest (think Pillow)

How does the Endocrine System communicate?

Hypothalamus & Pituitary Adrenal Axis (HPA)

Sarcomeres

A functional unit of muscle that is responsible for shortening & contraction of muscles.

• A single one won’t do much, so they have to work together

Type I Muscle Fibers (slow twitch)

• Contraction speed is slow

• Oxidative (uses O2 → Aerobic)

• Small fiber diameter

• high mitochondrial content

• high capillary density (more blood flow = more O2) “Red Fibers”

• Slow Relaxation Time

• Low Force Production

• low fatiguability (resistant to fatigue)

Type IIA (intermediates)

• between the other two

• fast twitch

• fast Oxidative glycolytic (Aerobic)- prefers to use O2 with glycogen

• intermediate fiber diameter

• intermediate mitochondrial content

• intermediate capillary density

• Fast relaxation (relaxes faster to produce another movement)

• intermediate force production

• intermediate fatiguability

• can be trained to be more like either of the other two types

Type IIX (Fast Twitch)

• fast glycolytic (anaerobic)

• large fiber diameter

• low mitochondrial content (doesn’t require O2)

• low capillary density (doesn’t need as much O2, so they don’t need much blood)- “White Fibers”

• Fast Relaxation Time (recover quick to continue quicker)

• high fatiguability (goes through fuel fast)

• high force production

Sliding Filament Theory: Cross Bridge Cycle

ATP → binds with the globular head on myosin and gets it ready to move calcium → binds with troponin → tells tropomyosin to move → opens the binding site on actin.

ATP Splits → ADP-P_I

myosin “pulls” action → sarcomere shortens

The “Interface”

motor unit → motor neuron + all the fibers that it innervates

X₁ Motor Neuron

fast-twitch (Type 2 fibers)

large

high recruitment threshold (activated with a lot of effort)

X₂ Motor Neuron

Slow-twitch (type 1 fibers)

small

low recruitment threshold (activated with little effort)

• can work immediately for long periods

• think posture muscles

Henneman’s Size Principle

smaller motor units are recruited first (most things early on have low force requirements) → posture, fine control

Large motor units are recruited as needed (body says we need this much for a specific weight)

I → IIa → IIx

Motor System

What drives the movement

Nervous System: Central vs Peripheral

CNS: Brain and Spinal Cord

Peripheral: Afferent and Efferent Neurons

Afferent Neuron

thing that relays the Action Potential (the signal) up the spinal cord.

Depolarization

changing outside charge with inside charge to send signal

Pathway ascending the spinal cord

→ Medulla → Thalamus (sorting station) → Frontal Cortex (motor interpretation) → Parietal Lobe (sensory) → “what to do?” - Info/commands are issued

Motor Cortex develops the motor plan → Thalamus → Pons medulla (helps coordinate the issued plans) → Action Potential (AP) goes down the descending spinal cord (DSC) → peripheral nerves → somatic system or autonomic system

If Somatic system → voluntary skeletal muscle- Alpha motor Neurons (motor Unit)

If the Autonomic system: involuntary, smooth muscle (think breathing and blood flow)

Reflex (bypass the Brain)

The spinal cord is programmed to react even without brain input when there is danger (think hand on hot stove → pulls back)

Cardiac Output (Q)

How much blood is being pumped by the heart in 1 minute. (HR x Stroke Volume mL/beat = Q L/min)

How much of Q goes to muscles and digestive organs & brain at rest

20% to the muscles due to lower output

80% to the digestive organs & brain

how much of Q goes to the muscle and digestive organs & brain during exercise?

80-85% to the muscles (we have a lot of muscles)

15-20% mostly goes to the brain and some to the skin 

Q_F (female)

4 L/min @ rest

Q_M (male)

5 L/min @ rest

Biggest Difference between Male and Female Q?

Stroke Volume (SV) due to heart size

• larger heart = larger ventricle = more blood being pushed out