Muscle Physiology and Function Review
PTA 104 Orthopedic Dysfunctions

Instructional Use Statement

The following information is used for instructional purposes for students enrolled in the Physical Therapist Assistant Program at Lane Community College. It is not intended for commercial use or distribution or commercial purposes. It is not intended to serve as medical advice or treatment.

Contact howardc@lanecc.edu for permissions.

Introduction

Now you get to apply your knowledge of kinesiology and therapeutic exercise while expanding your understanding of pathologies, impairments, functional limitations and disabilities affecting the musculoskeletal system. Before we move directly into movement-based rehabilitation, we need to revisit normal muscle and skeletal anatomy and physiology, principles of motor learning, and postural alignment.

Lesson Objectives

1. Review structure and function of the musculoskeletal system
2. Recall the significance of muscle fiber type (I and II) on power, fatigue, and recovery time in exercise
3. Recall terms to describe tissue mobility
4. Recall the physiology of a muscle contraction
5. Recall etiology of muscle strain
6. Recall and identify anatomical reference points for ideal standing and sitting posture
7. Review the physiology of stretching
8. Review the effects of immobilization on joint and soft tissue mobility
9. Describe factors which reduce joint mobility
10. Describe the effects of muscle length on postural alignment

Muscle Contraction - Sliding Filament Model

Lecture - narrated animation of how a muscle shortens

Watch and listen to the linked lectures before reading your Cameron text. Use your text to help support information provided in the lecture

Muscle Contraction Lecture 1

Muscle Contraction Lecture 2

• A sarcomere is a single contractile unit in a myofibril
• The significance of naming the bands and zones in a sarcomere is to distinguish anatomical reference points for the types of filaments (actin and myosin), where they overlap, and thus why muscle appears striated.
• Major contractile proteins in myofibrils are actin and myosin
• Concentric muscle contraction (shortening) relies on ATP as its energy source to catalyze the myosin head bond to actin filaments.
• Eccentric contraction involves the physical "breaking" of cross links between actin and myosin due to an applied load.
• Figure 5-3 in Cameron illustrates how the physical arrangement of the muscle relates to its function across its respective joint(s)
• (this is reinforced again in Kisner & Colby, so reading it twice is optional)
• Hundreds of thousands of myofibrils use energy and interactions between actin and myosin to produce a shortening contraction resulting in isometric, single joint, or functional movement.
• There are two basic types of muscle fibers: Type I (slow - twitch) and Type II (fast - twitch). Muscle function and training will determine the efficiency and effectiveness of Type I and Type II fibers.
• Muscle Fiber Type Self Check
• (note: for some reason it cuts off the text at top: Left is "type 1" stack, right is "type 2" stack)

Physiology of Stretching

• Muscle is comprised of contractile and noncontractile elements (i.e., soft tissue)
• Stretching - elongation of soft tissue
• Stress-Strain curve illustrates how the effect of a sustained load on soft tissue over time results in a lasting change in the length of the soft tissue
• Stress = load or force causing the strain; strain = elongation of the tissue as a % of its original length
• Creep describes how soft tissue will become increasingly stretched over time when the load on the soft tissue is constant;
• Relaxation describes how the soft tissue length decreases when the load is removed.
• Viscoelasticity of soft tissue is represented by the strength-strain curve; repetitive stretching allows for the soft tissue to experience greater strain (length) under the same stress (load)
• stretching in the elastic range will result in no change to muscle length - the tissue "bounces" back
• stretching in the plastic range will result in soft tissue lengthening by "breaking" collagen fibers; energy from breaking collagen is released as heat
• overstretching can result in tissue failure, tearing, strain and/or rupture

The safest form of stretching that achieves long term changes in muscle length is a static stretch. A constant load applied over time will allow the soft tissue to safely yield, target collagen fibers which restrict motion, yet protect from strain and/or tear.

Muscle Tissue Pathology

Disuse Atrophy

• The number of sarcomeres decrease with disuse
• The size of muscle cells decrease with disuse
• Connective tissue (non-contractile) loses its tensile strength with disuse
• Muscle tissue becomes stiffer (i.e., loses elasticity) with disuse
• Disuse can be resulty from acute injury, immobilization, primary disease, a secondary effect from disease, and/or a lifestyle choice
• Fast twitch muscle fibers (Type II) atrophy faster than slow twitch (Type I)

Muscle Strain

• Classifications range from overstretch to tissue failure (tear)
• Most common site of strain is where the muscle and tendon connect ("musculotendinous")
• May result when there is
• repetitive overuse
• sudden excessive loading beyond a muscle's capacity to resist the force
• overstretching
• Graded on a three-point scale: higher grade = more severe injury

Quiz and Unit One Exam Prep

Vocabulary Words - Research these terms in your Kisner & Colby readings

1. Hypomobility
2. Stretching
3. Flexibility - dynamic and passive
4. Contracture
5. Contraction
6. Hypermobility
7. Instability
8. Elasticity
9. Plasticity
10. Viscoelasticity
11. Collagen fibers
12. Creep

Time to refresh your A&P on the musculoskeletal system!

Questions to answer before you complete your weekly untimed quiz:

1. Do you know the difference between an osteoblast and an osteoclast?
2. Do you know what makes up a muscle fiber?
3. Can you recall the number of vertebra in each section of the spine?
4. Can you define "strain"?
5. Do you know the difference between Type I and Type II muscle fibers?
6. Can you understand and recall the definitions of the vocabulary words?
7. Do you know which soft tissues are the primary source of restricted range of motion?
8. Do you know the safest type of stretching?
9. Do you know the effects of immobilization on muscle tissue?

Role of the PTA

• Stretching is a therapeutic exercise: PTAs apply knowledge of kinesiology, soft tissue healing properties, and physiology when selecting, applying, and instructing in appropriate stretches
• PTAs must monitor for signs and symptoms of overstretching or for contraindications to applying a stretch to healing or fibrotic tissue
• PTAs must integrate understanding of the effects of immobility, age, and disease on tolerance to stretching
• PTAs measure ROM and assess changes in functional ROM and functional activities as a result of stretching
• PTAs modify techniques, positions, duration, etc. according to the patient-client response and report barriers to the supervising physical therapist
• PTAs educate patients and clients in the frequency, duration, and methods of stretching for injury managment and prevention

End Of Lecture