Muscle Stimulation & Exercise4-5 November 2014

Response to StimulationMuscles have graded responses – they contract to different

degrees, depending upon the frequency and strength of stimulation

Response to Stimulation If a nerve fires once

(unusual), the muscle contracts and relaxes in a twitch

If the nerve fires rapidly in succession, then the muscle does not relax fully in between impulses – resulting in tetany

(a smooth, prolonged contraction)

Response to Stimulation

Note:

tetanus ≠ tetanus

Tetanus (the type of muscle contraction) is different than tetanus the disease caused by a bacteria (commonly called lockjaw)

Response to Stimulation

The strength of contraction also depends on how many muscle fibers are stimulated.

The more muscle fibers stimulated, the greater the contraction of the muscle.

Quick Review

What vocab word describes the fact that muscles may contract to different degrees?

What two factors determine the extent to which a muscle contracts?

Graded response

Frequency of stimulation and number of cells stimulated

Muscle MetabolismMuscle contraction requires enormous amounts of energy in the form of ATP.

The amount of ATP stored in the cell only lasts for ~5 seconds!

The rest of the ATP must be regenerated, using one of three pathways.

Muscle MetabolismPathway 1: Direct phosphorylation by creatine phosphate

Fast!No O2 required

Quickly used upOnly in muscle

cells

Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation

Medium speed No O2 required

Less efficient Produces

lactic acid Only in muscle

cells

Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation

Misconception alert!

Lactic acid build-up

is not responsible for

muscle soreness the

day after exercise

(that’s due to cell

damage).

Muscle MetabolismPathway 2: Anaerobic glycolysis and lactic acid formation

Lactic acid build-up

is responsible for the

burning feeling

during exercise.

Also, lactic acid

build-up increases

muscle fatigue

(inability of muscle to

contract when

stimulated)

Muscle MetabolismPathway 3: Aerobic respiration

Slow Long-lasting All cells Requires O2

Muscle Metabolism

Which energy pathway is better?

CP and anaerobic supply energy at a fast rate (for maximum performance) but for a short term only.

Examples: Sprinting Any sport with bursts of energy & quick changes (e.g. Volleyball, b-ball) Start of exercise

Muscle Metabolism

Which energy pathway is better?

Aerobic can provideenergy for hours withoutfatigue

But, muscles are notworking at peak levels

Examples: cycling, marathon

Muscle Metabolism

Sports & Energy Systems

Muscle Metabolism

Oxygen DebtAll non-aerobic energy use causes changes in the muscle that need to be reversed after the exercise is over

O2, ATP, creatine phosphate, and glycogen reserves need to be replenished

Lactic acid needs be broken down

Oxygen debt is the extra amount of oxygen that must be taken in for these restorative processes.

This is why you breathe deeply for a while after intense exercise.

Think, Pair, Share

Scholar with shorter hair:Name the reactants and products of each energy system.

Which two energy systems are only used in muscles?

Scholar with longer hair:Which two energy systems lead to oxygen debt? Which energy system(s) predominate in the following activities: running for your life, hiking, lifting heavy furniture

Critical Thinking 1The graph below indicates the amount of lactic acid produced by muscle cells as a function of power (energy / time).

1) Describe how lactic acid production varies with power.

2) Explain

the shape of the

graph using

your knowledge

of energy

systems

Critical Thinking 11) Lactic acid increases very slowly from 150 W to 250

W but begins to increase dramatically at about 275 W.

2) At around 275 W, the rate of energy required by the muscle cells is too high, so the body switches from aerobic metabolism

to anaerobic

metabolism. This

point is known as

aerobic threshold.

Exercise & Muscles

Isotonic vs Isometric Contractions Isotonic contractions occur whenever the muscles shorten, causing movement

(e.g. weight lifting, running, swimming, jumping, etc.)

Isometric contractions occur whenever the muscle’s tension increases without actually shortening. This happens when you try to move an immovable object.

(e.g. pushing against a wall; many yoga exercises, etc.)

Exercise & Muscles

Aerobic vs Resistance ExerciseAerobic exercise (aka endurance or cardiovascular) – builds the aerobic endurance of muscles

Examples: jogging, biking Increases blood supply to muscles; # of mitochondria, &

amount of stored oxygen Benefits

Greater resistance to fatigue Better heart and lung function Improved digestion Improved bone density Reduced risk of metabolic disorder Increased immune system function

Exercise & Muscles

Aerobic vs Resistance ExerciseResistance exercise (aka weight training) – focuses on isometric contractions & forcing muscle to contract with as much force as possible

Examples: weights, some yoga exercises, pushups, situps, Increases the number of actin and myosin fibers, resulting in

larger muscles Benefits

Greater strength Greater muscle mass = greater metabolism Increased bone density

Exercise & MusclesExercise recommendations for healthy adults age 18-65 from CDC

Exercise & Muscles

Muscle tone and muscle wasting Muscles quickly deteriorate when not used

Lose 5-10% muscle mass per week with bed rest Lose 20% muscle strength in one week of bed rest Muscle strength plateaus at ~30% original strength after ~6

weeks of bed rest

Our body maintains muscle tone by systematically stimulating and partially contracting muscles around the body

Electrical muscle stimulators can also help prevent muscle atrophy following a stroke, injury, or surgery

Think, Pair, Share

1. Compare and contrast isotonic and isometric exercises, and provide an example of each

2. Compare and contrast resistance and aerobic exercise, and provide an example of each

3. Why is exercise necessary for our muscles?

4. How does exercise help our body function?

ClosureWhat were our objectives today?

What did you learn about these objectives?

How does what we learned today tie to our unit question?

Critical Thinking 2 – Exit TicketThe graph below indicates the amount of lactic acid produced by muscle cells as a function running pace.

1) Describe the data.

2) Explain

the data using

your

knowledge

of energy

systems and

exercise