Agonists are the main muscles responsible for the action. Antagonists oppose the agonists and can help neutralize actions. Since many muscles have

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Chastity Sherman
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2 *Agonists are the main muscles responsible for the action. *Antagonists oppose the agonists and can help neutralize actions. Since many muscles have more than 1 action sometimes a muscle has to neutralize one of its jobs to do another. For example, when the biceps contract, all 3 actions (shoulder flexion, elbow flexion, & supination) are initiated. However, to just do supination, the triceps (elbow and shoulder extensors) have to be innervated to not have flexion of the elbow and shoulder to take place. *Stabilizers typically imply isometric (static) contractions. They stabilize the body while the agonists do their job. 2

3 To have joint movement occur, the muscle tension and resistance forces will differ. *Concentric going against gravity or against resistance; muscle tension torque > resistance torque ex: the up phase of the bicep curl the biceps brachii concentrically contracting and overcoming the resistance to lift the weight *Eccentric going with gravity or going with resistance; muscle tension torque < resistance torque ex: the down phase of the bicep curl the biceps brachii is still the agonist, just eccentrically contracting now, because it s helping control the lowering of the resistance *Static no movement; muscle tension torque = resistance torque **One muscle (e.g., biceps brachii) or muscle group may produce a joint action (e.g., elbow flexion) and control the opposite action (e.g., elbow extension). ** 3

Torque is the strength occuring at the joint; it s a rotary force. T = Fr ---- Torque = Force X moment arm (r) *The moment arm can be manipulated 2 ways the joint angle and the insertion site.

4 Torque is the strength occuring at the joint; it s a rotary force. T = Fr ---- Torque = Force X moment arm (r) *The moment arm can be manipulated 2 ways the joint angle and the insertion site. Realistically, you can t do anything about changing an insertion site unless you went in surgically and moved it. So that leaves changing the joint angle. You can make the moment arm longer by manipulating the joint angle. *There are many things that can increase the force to increase the torque, but that is going more into biomechanics, so make sure you understand how to manipulate the moment arm for now in this class. 4

5 By increasing the moment arm, but keeping the force the same, you get an increase in torque! 5

6 Using the biceps brachii during elbow flexion as an example, which of these pictures has the bigger moment arm? Once again by having a bigger r (moment arm) you can have more strength! 6

7 In the static position above, the muscle force equals the resistance force. You re in a stuck position for those of you that do weight lifting you might recognize that as the sticking point where it seems harder than anywhere else in the range of motion in lifting weights. The weight doesn t change, but to make it easier and to get past that sticking point you can manipulate the moment arm. How would you do that? 7

8 You typically do calf raises with your knee extended. So even though the gastrocnemius does knee flexion and plantar flexion, to really work the gastrocnemius you do calf raises standing with knees extended while doing plantar flexion. 8

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This will go much more in depth in biomechanics, but it is important to at least be introduced to the concept to understand how force production can be affected in muscles, especially biarticular

10 This will go much more in depth in biomechanics, but it is important to at least be introduced to the concept to understand how force production can be affected in muscles, especially biarticular muscles. When shortened to around 50% to 60% of resting length ability to develop contractile tension is essentially reduced to zero. Stretch beyond 100% to 130% of resting length significantly decreases the amount of force muscle can exert. 10

11 Stretch beyond 100% to 130% of resting length significantly decreases the amount of force muscle can exert 11

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16 You will be doing a couple labs practicing this think of exercises you do at the fieldhouse and try to dissect them. For example, lat pull-downs or the bench press. What is happening at the shoulder, scapula, elbow, hip, knee, ankle, etc? 16

(1) Position = Elbow flexed, shoulder extended, scapular retraction (2) Position = Elbow extended, shoulder flexed, scapular protraction agonist muscles contracted: triceps and anconeus (elbow

17 (1) Position = Elbow flexed, shoulder extended, scapular retraction (2) Position = Elbow extended, shoulder flexed, scapular protraction agonist muscles contracted: triceps and anconeus (elbow extension), anterior deltoid, coracobrachialis, pectoralis major, biceps (shoulder flexion), pectoralis minor, serratus anterior (scapular protraction). So the agonist muscles for a push-up are the pectoralis major, biceps (shoulder flexion), triceps (elbow extension), and serratus anterior, pec minor (scapular protraction). They are working concentrically during the up phase, and then eccentrically during the down phase they are the agonists for both phases! *What would be an antagonist from those muscles? What muscle and its action has to be neutralized? *What are stabilizing muscles?? They would be the spine and hip flexors without them the hips would sag and cause hyperextension of the hip and spine! 17

(1) Position = Hips flexed, knees flexed, ankle dorsiflexion (2) Position = Hips extended, knees extended, plantar flexion Now coming up from a squatted position to reach position 2, the quadriceps

18 (1) Position = Hips flexed, knees flexed, ankle dorsiflexion (2) Position = Hips extended, knees extended, plantar flexion Now coming up from a squatted position to reach position 2, the quadriceps (knee extension), gluteus muscles & hamstrings (hip extension), and gastrocnemius, soleus, tibialis posterior (plantar flexion) are the agonist muscles and they are concentrically contracting. However, going down to a squat to reach position 1 (the downward movement) is going with gravity and so the prime movers are still the knee extensors, hip extensors, and plantar flexors just this time they are working eccentrically. If you were to say that the agonist muscles were the hip flexors, knee flexors, and dorsiflexors during the down phase of a squat, you would be incorrect the knee and hip extensors as well as the plantar flexors are still the agonists working eccentrically to slow the body coming down with gravity, and to not bottom out with all the weight. Name all of the knee extensors, hip extensors, and plantar flexors 18

19 Check out the videos to these exercises that show the muscle animations occurring during the movements. Make sure you can identify the agonists in the exercise and when they are eccentric and concentric. When doing knee extension (shown in the picture) you are going against gravity and so the quadricep muscles are concentrically contracting and are the agonists for the movement. When bringing the weight back down, you are going with gravity and so the quads are eccentrically contracting by keeping the weight in check and bringing it back down in a slow, controlled manner. 19

20 The agonists for this exercise are the deltoids (shoulder abduction), serratus anterior and trapezius (scapular upward rotation). They are concentrically contracting during the up phase and then eccentrically contracting during the down phase they are bringing the weight down slowly and in a controlled manner. The elbow is in extension throughout the entire exercise meaning it is static, as well as the wrist extensors and finger flexors. 20

21 By bending over you are doing a completely different action at the shoulder joint than you were with just lateral arm raises. You are now doing shoulder horizontal abduction and the agonists for that are the deltoid and infraspinatus. Scapular retraction is done by the rhomboids and trapezius. The elbow, wrist, and fingers are like the lateral arm raises on the previous slide. Once again they are concentrically contracting during the up and out phase and then eccentrically contracting during the down phase they are bringing the weight down slowly and in a controlled manner. Spine extensors, head extensors, and knee extensors are static and working as stabilizers for the body throughout the exercise. 21

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