Exercise Physiology Unit 3

most important type of muscle for movement

skeletal muscle

T/F: To go from rest to standing requires only one step.

False

Very important process that makes movement possible

motor unit recruitment

What tells the muscles to do work and determines when/if motor units are recruited?

nervous system

Low force activities recruit _______ and ______ motor units.

fewer and smaller

High force activities recruit ______ and _____ motor units.

more and larger

muscle fiber that is:

-rich in myoglobin & mitochondria

-weakest contraction out of 3 fiber types

-Used in lower-intensity exercise

type I

muscle fiber that is:

- most forceful fibers

-have the lowest time of contraction

-easiest to fatigue

-fastest contracting skeletal muscle fibers

type 2x

Thought to be the most trainable muscle fiber and can take on characteristics to shift towards 2x to become more forceful and can also take on characteristics to shift towards I to become more endurance focused

2a

more forceful muscle fibers

type 2x

more endurance focused muscle fibers

type i

order of muscle recruitment

Type I --> type 2a --> type 2x

nerve cell that directly controls skeletal muscle contraction

alpha motor neuron

Alpha motor neuron has a long axon covered by _____ and have terminals that attach to what?

myelin ; muscle fibers

Space between the terminal and the muscle fiber is known as the...

synaptic cleft

neurotransmitter that is released at the neuromuscular junction

Acetylcholine (ACh)

What happens when ACh is released into the synaptic cleft?

It binds to ACh receptors on the muscle fiber.

What does ACh binding cause in the muscle fiber?

Depolarization of the muscle membrane, which initiates contraction.

The connection between the alpha motor neuron, synaptic cleft, and muscle fiber where ACh is released and muscle activation begins.

neuromuscular junction

What allows the muscle action potential to spread deep into the muscle?

T-tubules

The action potential traveling down the T-tubules triggers what?

release of calcium from the sarcoplasmic reticulum

role of calcium in muscle contraction

allows actin and myosin to form cross-bridges, enabling contraction.

What stops muscle contraction?

Calcium is pumped back into the sarcoplasmic reticulum, ending cross-bridge formation.

Muscles make up about ___% of one's body weight

40%

Muscle is comprised of...

70% water

20% protein

< 10% is salt, minerals, & substrates (phosphocreatine, ATP, glucose, etc)

function of tendons

attach to bone from muscles and pull to create movement

singular muscle fiber is called...

Myofibril

each muscle fiber has around _______ Sarcomeres

2000

T/F: Myofibrils is where contraction is actually happening

T

2 parts of actin that act as regulatory proteins for muscle contraction

Tropomyosin and myosin

covers the myosin-binding sites for contraction at rest

tropomyosin

removes tropomyosin from the active site so contraction can occur

troponin

Has globular heads that rotate 360 degrees, and wants to interact with actin

myosin

What happens if tropomyosin is covering the myosin-binding site on actin?

myosin can't bind and contraction can't happen

What happens when Ca2+ binds to troponin?

it moves tropomyosin off of the binding/active site so that muscle contraction can occur

sliding filament theory

The sliding filament theory explains how muscles contract. It says that myosin "heads" pull on actin filaments, causing them to slide past each other. This sliding makes each sarcomere shorter, which causes the whole muscle to shorten and produce force.

enzyme located on the myosin head that hydrolyzes ATP → ADP + Pi, releasing energy

Myosin ATPase

Provides the actual energy for the sliding of myosin and actin to occur

Myosin ATPase

increasing size AND number of muscle fibers

hyperplasia

Who does hyperplasia happen to?

seen in animals, there is debate if it happens in humans or not (most believe it does not happen), and seen in some body builders

taking individual muscle fiber and thinking about it like a balloon (expanding), still same fiber but the size is enlarged

hypertrophy

T/F: Men experience a greater absolute change in muscle size because of their larger initial muscle mass, but muscular enlargement on a percentage basis remains similar between genders.

True

T/F: Sex differences in hormonal response to resistance exercise may determine any ultimate sex differences in muscle size/strength adaptations with training.

true

sensors that detect stretch, tension, and pressure in the muscles and tendons

Proprioceptors

How do proprioceptors work?

Almost instantaneously relay information about muscular dynamics and limb movement to conscious and subconscious portions of the CNS

What do proprioceptors allow for?

The CNS to continually monitor and adjust ongoing movements

Proprioceptors located within the muscle belly that detect changes in muscle length and the rate of length change; detect muscle stretch and trigger a reflex contraction to counteract the stretch

muscle spindles

What type of sensory information do muscle spindles provide?

Mechanosensory information about muscle fiber length, stretch, and speed of stretch.

What primarily activates muscle spindles?

Stretch of the muscle

Why are muscle spindles important?

protect muscles from overstretching and help maintain posture and joint stability

The number of spindles within a muscle depends on...

the function of the muscle

Which muscles have the highest density of muscle spindles?

muscle involved in complex movements

T/F: Muscles involved in more complex movements have more muscle spindles/gram of tissues.

True

Muscle spindle response depends on ______ and ______.

The amount and rate of muscle stretch

____ sensory afferent fibers and ____ motor efferent fiber innervate the muscle spindle.

2 ; 1

specialized sensory muscle fibers within a muscle spindle that detect stretch

intrafusal fibers

the main, large fibers outside the spindle that generate force and movement

extrafusal fibers

What does the muscle spindle detect in the stretch reflex?

Changes in the length of extrafusal muscle fibers

detects, responds to, and modulates changes in the length of the extrafusal muscle fibers to provide an important regulatory function for movement and maintenance of posture

stretch reflex

3 components of stretch reflex

-Muscle spindle that responds to stretch

-Afferent nerve fiber that carries the sensory impulse from the spindle to the spinal cord

-Efferent spinal cord motor neuron that activates the stretched muscle fibers

sensory proprioceptors found at the junction between muscle fibers and the tendon

golgi tendon organs

Golgi tendon organs detect....

differences in the tension generated by active muscle

Role of golgi tendon organs

protect muscle fibers and surrounding connective tissue from injury due to sudden or excessive load

If tension becomes too high, what do the GTO do?

send a strong inhibitory signal to the spinal cord, which causes the muscle to relax

GTOs respond to tension from two sources:

-tension created when the muscle contracts (shortens)

-tension when the muscle stretches passively

When the muscle shortens and generates force, the tendon tightens and GTO is ________.

activated

If the muscle is lengthened by an external force, tension increases and GTO is _______.

activated

What happens when Golgi tendon organs (GTOs) are stimulated?

They transmit signals to the spinal cord, causing reflex inhibition of the muscles they supply.

Changes in muscle size become detectable after only _______ weeks of training

3-4

n increase in muscle size due to training or repeated stress

hypertrophy

During resistance training or intense exercise, what happpens to muscle fibers?

undergo tiny injuries (microtears)

How does body respond to microtears in muscle fibers?

by accelerating protein synthesis to repair the fibers

Protein breakdown _______ relative to synthesis after microtears.

decreases

The repair process of muscle fibers overcompensates, making muscle fibers _____ and _____ .

strong and larger

cells that are activated by muscle stress or injury, proliferate, and fuse with existing muscle fibers to help repair and grow the fiber

satellite cells

T/F: Satellite cell activation contribute to myofibril thickening by providing new nuclei, which allow the muscle fiber to synthesize more actin and myosin, thickening the myofibrils and adding additional sarcomeres.

true

Muscle _______ is depleted during intense exercise because it is used for energy.

glycogen

How do muscles restore glycogen after intense exercise?

GLUT4 transporters move to the cell membrane to increase glucose uptake, and enzymes for glycogen storage are upregulated

Muscle damage can be clinically measured by measuring ______ and ______ levels in the blood.

calcium (Ca²⁺) ; creatine kinase (CK)

Which hormones are released in response to exercise stress?

ACTH from the pituitary and cortisol from the adrenal glands

Hormone that suppresses inflammation

and accelerates breakdown of muscle protein into amino acids for energy or repair during intense exercise

cortisol

How long can recovery and adaptation processes last after intense exercise?

Up to 72 hours post-exercise.

After an initial bout of intense exercise, muscles adapt, causing less damage, soreness, and more efficient glycogen resynthesis during subsequent bouts.

repeated bout effect

Carbohydrate + Protein intake after exercise helps...

Restore glycogen

Provide amino acids for repair

Stimulate an anabolic environment (muscle-building)

Anabolic State for Muscle Growth requires what two things?

energy surplus and positive nitrogen balance

To minimize fat gain during an anabolic state of training, what kind of proteins should you eat?

lean proteins (chicken/fish) vs. fatty ones (beef/lamb)

Fat loss requires an energy _______, which is a ______ state

deficit ; catabolic

To minimize muscle loss during an energy deficit, increasing protein intake by _____% would be suitable to maintain nitrogen balance.

>20%

After exercise, the environment of the body is anabolic or catabolic?

catabolic

Post exercise, what promotes an anabolic state?

feeding

How does feeding promote an anabolic state?

-Increases amino acid pool

-Elevated plasma insulin reduces protein breakdown

What should you eat after exercise?

A mixed meal is recommended with at least 1g of carbs/kg body weight and 0.5g protein/kg body weight

What happens if feeding is delayed by 24 hours post exercise?

net protein balance is negative and no muscle hypertrophy occurs.

What benefits does ingesting carbohydrates first have on post-exercise consumption?

Shifts environment to the "fed" state by and may limit the oxidation of absorbed amino acids

Effect of amino acids on protein synthesis is _____ if CHO is consumed before protein.

delayed

T/F: Insulin levels are very low at the end of exercise, and consuming carbohydrates would maintain them and decrease protein oxidation.

True

Successful muscle growth depends on what 3 fators?

nutrition timing

energy balance

monitoring training load

Key stimuli for muscle hypertrophy

stress (exercise), nutrition, hormones

For muscle hypertrophy, a kcal ______ is recommended.

surplus

T/F: Protein and exercise go hand in hand. You won't gain muscle from just protein alone, you need to exercise as well.

True