1. Chapter 2 Neuromuscular Fundamentals PPT Series 2B
EXSC 314
Chapter 2 Neuromuscular Fundamentals PPT Series 2B

2. Types of Muscle Contraction
Contraction - When tension is developed in a muscle as a result of a stimulus
To slow down or decelerate the movement of a body segment
To prevent the movement of a body segment by external forces
In some contractions the muscle does not shorten in length
All muscle contractions are either isometric or isotonic
Muscle contractions can be used to cause, control, or prevent joint movement or:
To initiate or accelerate the movement of a body segment

3. Isometric Contraction
Active tension is developed within the muscle but joint angles remain constant
What are functional benefits of isometric types of contractions?

4. Isotonic Contraction
Involve the muscle developing active tension to either cause or control joint movement
Dynamic contractions
The varying magnitude of tension (force development) in muscles result in joint angles changing
Isotonic contractions are either concentric or eccentric on the basis of whether shortening or lengthening occurs

5. Types of Muscle Contraction
Movement may occur at any given joint without any muscle contraction.
Referred to as passive movement
Movement is solely due to external forces, such as those applied by another person, object, or resistance, or to the force of gravity in the presence of muscle relaxation

6. Types of Muscle Contraction
Concentric contractions involve a muscle developing active tension as the muscle fibers shorten. (positive contraction) Eccentric contractions involve the development of active tension as muscle fibers lengthen (negative contraction)

7. Concentric Contraction
Muscle develops active tension as it shortens
Force developed by the muscle is greater than that of the resistance
Occurs when muscle develops enough force to overcome applied resistance
Results in the joint angle changing in the direction of the applied muscle force
Causes movement against gravity or resistance
Causes the body part to move against gravity or external forces

8. Eccentric Contraction
Muscle lengthens contractions involve the development of active tension as muscle fibers lengthen.
Muscle force production controls the descent of resistance
Weight or resistance is greater than the force of the muscle contraction but not to the point that the muscle cannot control descending movement

9. Isokinetics
A type of dynamic exercise using concentric and/or eccentric muscle contractions
Speed (or velocity) of movement is constant (controlled)
Muscular contraction (ideally maximum contraction) occurs throughout movement
Example – Biodex :

10. Role of Agonist Muscles
Cause a desired joint motion through a specified plane of motion when contracting concentrically Known as primary or prime movers, or as muscles most involved
What would be the prime mover or agonist of elbow flexion?

11. Role of Agonist Muscles
Assisters or assistant movers
Are agonist muscles that contribute significantly less to the joint motion.
Example: In the flat bench press, the pectoralis major would be a prime mover in flexing and adducting the humerus, whereas the anterior deltoid would be an assistive mover in flexing the humerus.

12. Role of Antagonist Muscles
Known as contralateral muscles. Located on the opposite side of joint from the agonist.
When contracting concentrically, they perform the joint motion opposite to that of the agonist
May assist the work of the agonist muscles by relaxing and allowing movement
Example - Quadriceps muscles are antagonists to hamstrings in knee flexion

13. Role of Stabilizer Muscles
Known as fixators
Stabilizing muscle contraction are essential in establishing a firm base for the more distal joints to work. Stabilizers contract to fixate or stabilize the area to enable another limb or body segment to exert force and produce movement.

14. Role of Stabilizer Muscles
Example - Biceps curl
Muscles of the scapula and the glenohumeral joint must contract in order to maintain the shoulder complex and humerus in a relatively static (stable) position so that the biceps brachii can more effectively perform curls
The antagonists for each motion of the proximal joint co- contract or contract against each other to prevent motion
This is an example of proximal stabilization to enhance the effectiveness of distal joint motion, which occurs commonly with the upper extremity

15. Role of Synergist Muscles
Assist in the action of agonists and are also called “guiding muscles”
Assist in refined movement and rule out undesired motions and are not necessarily prime movers for the desired action.
They may be sub-classified as helping synergists or true synergists

16. Role of Helping Synergist Muscles
Helping synergists:
Have agonist and antagonistic actions but they can also assist another muscle move the joint in the desired manner and simultaneously prevent undesired actions.
Example - Anterior and posterior deltoid
Anterior deltoid and posterior deltoid have agonistic and antagonistic actions on humeral flexion and extension.
But both work synergistically with the middle deltoid to accomplish humeral abduction

17. Role of True Synergist Muscles
True synergists
Contract to prevent an undesired joint action of the agonist and have no direct effect on agonist action
Example - Finger flexors are provided true synergy by wrist extensors when grasping an object
Finger flexors originating on the forearm and humerus are agonists in both wrist flexion and finger flexion
Wrist extensors contract to prevent wrist flexion by finger flexors
This allows finger flexors to maintain more of their length and therefore utilize more of their force in flexing the fingers

18. Role of Neutralizer Muscles
Neutralizers
Counteract or neutralize the action of another muscle to prevent undesirable movements .
The contraction of neutralizing muscles resists specific actions of other muscles
Example 1 - When only the supination action of the biceps brachii is desired, the triceps brachii contracts to neutralize the flexion action of the biceps brachii
Example 2 - Biceps curl - When only the flexion force of the biceps brachii is desired, the pronator teres contracts to neutralize the supination component of biceps

19. Role of Force Couple Muscles
Force couples
Occur when two or more forces are pulling in different directions on an object, causing the object to rotate about its axis, and producing a more efficient movement.
Example - Middle trapezius, lower trapezius, and serratus anterior each pull on the scapula from a different direction to produce the combined result of upward rotation

20. Tying the Roles of Muscles Together
If there are muscles with multiple agonist actions:
Attempt to perform all of their actions when contracting, and cannot determine which actions are appropriate for the task at hand.
Thus actions performed depend upon several factors
The motor units activated
Joint position at the time of contraction
Planes of motion allowed in the joint
Axis of rotation possible in the joint
Muscle length
Relative contraction or relaxation of other muscles acting on the joint

21. Tying the Roles of Muscles Together
Two muscles may work in synergy by counteracting their opposing actions to accomplish a common action.
Example: Kicking A Ball - Muscles primarily responsible for hip flexion and knee extension are agonists.
The hamstrings are antagonistic and relax to allow the kick to occur. The preciseness of the kick depends on the involvement of many other muscles.

22. Example of Muscle Roles in Kicking a Ball
The lower extremity route and subsequent angle at the point of contact (during the forward swing) depend on a certain amount of relative contraction or relaxation in the hip abductors, adductors, internal rotators, and external rotators (acting in a synergistic fashion to guide lower extremity precisely)
These synergistic muscles are not primarily responsible for knee extension and hip flexion but contribute to the accuracy of the total movement.
These synergistic muscles in contralateral hip and pelvic area must be under relative tension to help fixate or stabilize the pelvis to provide a relatively stable base for the kick to occur on the opposite side.

23. Tying the Roles of Muscles Together
Antagonistic muscles produce actions opposite to those of the agonist.
Reversal of Muscle Function
A muscle group described to perform a given function can contract to control the exact opposite motion.

24. Determination of Muscle Action
Variety of methods
Anatomical dissection
Palpation
Models
Electromyography
Electrical stimulation
Consideration of anatomical lines of pull

25. Determination of Muscle Action - Palpation
Using the sense of touch to feel or examine a muscle as it contracts
Limited to superficial muscles
Helpful in understanding of joint movement
Models
Long rubber bands may be used as models to simulate muscle lengthening or shortening as joints move through ranges of motion

26. Determination of Muscle Action - Electromyography (EMG)
Utilizes either surface electrodes which are placed over muscle or fine wire/needle electrodes placed into muscle
As the subject moves the joint and contracts muscles, the EMG unit detects the action potentials of muscles and provides an electronic readout of contraction intensity and duration
Most accurate way of detecting the presence and extent of muscle activity

27. Determination of Muscle Action - Electrical Muscle Stimulation
Reverse approach of electromyography
Uses electricity to cause muscle activity
Surface electrodes are placed over muscle and the stimulator causes muscle to contract
Joint actions may then be observed to see the effect of the muscle’s contraction

28. Determination of Muscle Action - Lines of Pull
Consider the following:
Exact locations of bony landmarks of a muscle’s proximal and distal attachment and their relationship to joints
Planes of motion through which a joint is capable of moving
Muscle’s relationship or line of pull relative to the joint’s axes of rotation

29. Determination of Muscle Action - Lines of Pull
Consider the following:
As a joint moves the line of pull may change and result in muscle having a different or opposite action than in the original position
Potential effect of other muscles’ relative contraction or relaxation on a particular muscle’s ability to cause motion
Effect of a muscle’s relative length on its ability to generate force
Effect of the position of other joints on the ability of a biarticular or multiarticular muscle to generate force or allow lengthening
End of PPT Series 2B