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

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

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

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

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

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)

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

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

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 :

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?

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.

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

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.

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

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

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

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

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

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

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

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.

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.

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.

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

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

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

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

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

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