Muscle PerformancePTA 130 – Fundamentals of Treatment I

Introduction to muscle performance Discuss anatomical considerations of muscle Describe various types of resistance training Describe muscle adaptation to resistance training

Lesson Objectives

The capacity of a muscle to do work W = force x distance A complex component of functional movement and

is influenced by all of the body systems Key elements of muscle performance include: ◦ Strength◦ Power◦ Endurance

Muscle Performance

Muscle tissue is made up of contractile and noncontractile tissues

Connective tissue structures are: ◦ Endomysium (innermost layer)◦ Perimysium ◦ Epimysium (envelops the entire muscle)

Muscle Structure (Figure 4.2)

Individual muscles are composed of muscle fibers A single muscle fiber is made up of many myofibrils Each myofibril is composed of the smallest

contractile units known as sarcomeres Sarcomeres are composed of overlapping

myofilaments of actin (thin) and myosin (thick) What happens to the actin-myosin filaments when a

muscle actively shortens?

Muscle Structure – cont’d

Structure of Skeletal Muscle

Sarcomere = from Z-disc to Z-disc Contraction is triggered by a stimulatory

nerve impulse that causes an action potential to spread across the sarcomere

The action potential stimulates the sliding of filaments to occur

A change in muscle length results

Sliding Filament Theory

Structure of a Sarcomere

A functional structure consisting of a motor neuron and the muscle fibers it innervates

Larger muscles are made up of more muscle fibers◦ Produce less specific movements

Smaller muscles are made up of fewer muscle fibers◦ Produce very specific movements

Examples:◦ A motor unit inside the eye will usually contain two to three fibers, with

only three to five motor units residing in the entire eye. ◦ The calf muscle can have between 1,000 and 2,000 motor fibers per

motor unit.

Motor Unit

Dependent upon many factors: ◦ Biological ◦ Neurological ◦Metabolic◦ Biomechanical factors◦ Energy stores available to muscle◦ Influence of fatigue and recovery from exercise◦ Age◦ Gender

Tension Generation in Normal Skeletal Muscle

The diminished response of muscle to a repeated stimulus

Occurs during exercise when a muscle repeatedly contracts statically or dynamically against an imposed load

Muscle fatigue is normal and reversible The rate at which muscle fatigue occurs is also

dependent upon the type of muscle fibers involved

Muscle (local) fatigue

Affects how resistant the muscle is to fatigue Two broad categories: ◦ Type I

Slow-Twitch◦ Type II

Fast-Twitch

Fiber-Type Distribution of Muscle

Type I fibers Tonic, slow-twitch Generate low level of muscle tension Can sustain the contraction for a long period of time More resistant to fatigue For prolonged, sustained aerobic activity What muscle(s) are composed primarily of Type I

fibers?

Slow-Twitch Muscle Fibers

Type II fibers Generate a great amount of tension within a short

period of time For brief, intense anaerobic activity More force production possible because of greater

muscle fiber numbers in motor unit What muscle(s) are composed primarily of Type II

fibers?

Fast-Twitch Muscle Fibers

Type I vs. Type II Muscle Fiber Contraction Rates

Muscles are composed of both slow- and fast-twitch fibers

Ratios of each type vary from muscle to muscle and from person to person

Fast and Slow Twitch

Irritability: ◦ Stimulation is required to produce a response. ◦ Threshold = minimum stimulation required for a response

Contractility: ◦ Ability to contract = twitch. ◦One contraction occurs with each stimulus ◦ Sustained contractions: require repeated stimuli

Physiological Properties of Skeletal Muscle

Excitability◦ Capacity of muscle to respond when stimulated by nerve

impulse Extensibility (stretchability)◦ Capacity of muscle to stretch beyond its relaxed length

Elasticity◦ Ability to return to original length after contraction or

stretching

Terminology

Extensibility and Elasticity: ◦ As muscle is stretched, it becomes more extensible◦ Inactivity produces stiffness◦ Stiffness can be overcome with active exercise (which

increases temperature, decreases viscosity, and improves extensibility)

Physiological Properties of Skeletal Muscle

Muscle Contracture: ◦ The failure of a muscle to relax; it is normal for muscle to relax

after contraction ◦ Fatigue reduces the ability to produce maximum contraction

and to completely relax◦ It is important to stretch after activity since fibers do not

resume normal length with fatigue◦Muscle contracture is not the same as orthopedic contracture

(connective tissue shortening) or muscle spasm

Physiological Properties of Skeletal Muscle

Fatigue: ◦ Related to contracture ◦ From exhaustion of muscle with activity or from inadequate

circulation to provide nutrients needed for continued activity◦ Lactic acid: builds up with inadequate amount of oxygen to

metabolize it◦ Endurance proportional to tolerance of pain produced by

lactic acid buildup: tolerance endurance

Physiological Properties of Skeletal Muscle Fatigue

Fatigue:◦ Lactic acid production varies:

Untrained muscles produce more lactic acid than trained muscles Type II muscle produce more than type I muscle High intensity exercises produce more than low

◦ Sustained isometric exercises: block blood flow to increase lactic acid buildup fatigue (e.g., carrying suitcase: grip)

Physiological Properties of Skeletal Muscle Fatigue

The type of resistance training selected for a therapeutic exercise program are dependent on many factors: ◦ Cause and extent of impairments◦ Stage of tissue healing◦ Condition of joints◦ General abilities of the patient◦ Patient’s goals and intended functional outcomes

Types of Resistance Training

Static◦ Isometric

Dynamic ◦ Isotonic◦ Isokinetic

Types of Muscle Activity

◦ Force produced in muscle without a change in the muscle’s length; no visible joint motion

◦ Advantages: Strengthen muscle without undue stress (no change in position) Can start early (e.g., surgery, fracture) Appropriate when muscle is too weak for active range of motion

against gravity, isotonic, or isokinetic exercises

Isometric Exercise (Static)

Muscle – setting exercises◦Quad sets◦ Glut sets◦ Hamstring sets

Stabilization exercises◦ Core stabilization◦ Rhythmic stabilization

Types of Isometric Exercise

Intensity of muscle contraction◦ Exercise intensity load of 60-80% of a muscle’s force

Duration of muscle activation◦ 6-10 second hold during contraction

Repetitions performed depends upon◦Muscle’s condition◦ Ability of part to move◦ Healing phase of tissue

Characteristics of Isometric Exercise

Precaution - Valsalva maneuver:◦ Breath – holding commonly occurs during isometric exercise◦ Causes a rapid increase in blood pressure◦ It is important to emphasize exhalation during the contraction

Isometric Exercise

Causes joint movement and a change in length of muscle tissue

Concentric Contraction – ◦Muscle contracts and shortens

Eccentric Contraction – ◦Muscle lengthens under tension

Concentric and eccentric contractions are involved in most activities

Dynamic Exercise

A form of dynamic muscle loading where tension in a muscle develops and physical shortening of the muscle occurs as an external force (resistance) is overcome

Example?

Concentric Exercise

Involves dynamic loading of a muscle beyond its force-producing capacity, causing physical lengthening of the muscle as it attempts to control the load

Example?

Eccentric Exercise

Both types of exercise have value in rehabilitation programs

A combination of both concentric and eccentric activities occur in our daily life

Are concentric or eccentric exercises more difficult to perform?

Why?

Concentric vs. Eccentric

Type of dynamic activity Velocity of muscle shortening or lengthening is

maintained, but force varies through range of motion The term isokinetic refers to movement that occurs

at an equal velocity Also known as accommodating resistance exercise Offers reciprocal training of agonist and antagonist

Isokinetic Activity

QUESTIONS?