Laboratory Activity – Introduction to Movement Analysis



Name

Lab Section

PEP 300 - Laboratory

Performing a Muscular Analysis – Part 2

Purpose: To practice performing an in-depth muscular analysis of a movement pattern or skill.

Equipment: Lab Handout

Video clips of common skills (to be provided by instructor)

Background:

One of the most important principles of training is specificity. This principle teaches us that we should develop exercise routines based on the needs of the exerciser and on the activity for which s/he is training. Specificity should address the anatomical, biomechanical, physiological, and neurological demands of the activity. Within these four areas there are many aspects that must be considered. One of the most important aspects is identification of which muscles are being used and how those muscles are being used. This constitutes a muscular analysis. We can apply a muscular analysis in two ways. First, we can analyze the skill or activity that we are training for so that we know which muscles are being used and how those muscles are being used. Second, we can analyze training and conditioning exercises to determine which muscles are being used and how those muscles are being used. With these two pieces of information, we are able to select training and conditioning exercises that are most appropriate for training for the activity we are interested in.

Procedures to be completed prior to lab:

1. Read the assigned material listed on your course syllabus.

2. Review the steps for conducting a muscular analysis as discussed in lecture and outlined on the handout – Performing a Muscular Analysis.

Procedures to be completed during the lab session:

1. Perform a muscular analysis of the vertical jump shown in the video provided by the instructor by answering the following questions:

a. Complete the chart below for the shoulder joint for the portion of the vertical jump from the beginning of the movement to takeoff from the ground. You should identify as many phases as you think appropriate.

|Phase |Early Countermovement |Mid Countermovement |Late Countermovement |Execution |

|Joint |Shoulder |Shoulder |Shoulder |Shoulder |

|Joint Action |flexion |extension |extension |flexion |

|Plane/Axis of Motion |sagittal/ML |sagittal/ML |sagittal/ML |sagittal/ML |

|Motive Torque |muscle |muscle |inertial force of arm |muscle |

|Resistive Torque |weight of arm |weight of arm |muscle |inertial force of arm & |

| | | | |weight of arm |

|Muscle Action |concentric |concentric |eccentric |concentric |

|FMG |shoulder flexors |shoulder extensors |shoulder flexors |shoulder flexors |

|Developing Force | | | | |

|Agonists |shoulder flexors (anterior|shoulder extensors (posterior|shoulder extensors (posterior|shoulder flexors (anterior |

|(FMG’s and individual |deltoid, coracobrachialis,|deltoid, latissimus dorsi, |deltoid, latissimus dorsi, |deltoid, coracobrachialis, |

|muscles) |biceps brachii, pectoralis|pectoralis major – sternal |pectoralis major – sternal |biceps brachii, pectoralis |

| |major – clavicular |portion) |portion) |major – clavicular portion) |

| |portion) | | | |

|Antagonists |shoulder extensors |shoulder flexors (anterior |shoulder flexors (anterior |shoulder extensors (posterior|

|(FMG’s and individual |(posterior deltoid, |deltoid, coracobrachialis, |deltoid, coracobrachialis, |deltoid, latissimus dorsi, |

|muscles) |latissimus dorsi, |biceps brachii, pectoralis |biceps brachii, pectoralis |pectoralis major – sternal |

| |pectoralis major – sternal|major – clavicular portion) |major – clavicular portion) |portion) |

| |portion) | | | |

b. Identify and discuss any two examples of rotary stabilization that are occurring during the skill (these do not have to involve the shoulder joint). Be sure you identify the segment/joint that is being stabilized, the muscle (individual or group) that is(are) acting as the stabilizers, and the force that is being stabilized against.

There are not very many examples of rotary stabilization in this skill, most of the segments are moving throughout the skill. One example would be stabilization of the wrist by the radial and ulnar deviators against gravity and the inertial forces created during the movement. A second example is that of the trunk. It is being stabilized by the flexors and extensors of the trunk, again against gravity and the inertial forces created during the movement.

c. Identify and discuss two examples of neutralization that are occurring during the skill (these do not have to involve the shoulder joint). Be sure you identify the muscle whose action is being neutralized, and the muscle (individual or group) that is(are) acting as the neutralizer(s).

To examine neutralization, examine the specific scenarios that we identified in lecture.

• Does the scapula or pelvis have to be stabilized to provide a firm base from which muscles that move the femur and humerus can pull? Yes, all of the shoulder flexors and shoulder extensors (except the sternal pectoralis major) acting in this movement attach proximally to the scapula and/or the clavicle. Because the scapula and clavicle are lighter than the humerus & forearm, they tend to move when any of these muscles contract. Therefore, we have to keep this from happening. The line of pull of the proximal attachment sites for each of these muscles probably causes the scapula to protract and depress. Therefore, we would need to recruit the retractors and the elevators to stabilize the scapula against these movements. What are the specific muscles that elevate and retract the scapula? Would all of these muscles be recruited? Other examples of neutralization under this scenario may be occurring in the lower extremity as well because many of the agonists at the hip and knee have their proximal attachments on the pelvis. Can you identify any of these examples?

• Is there a multijoint muscle in the agonist or antagonist FMG developing force that may be causing unwanted action at its other joints? Let’s look at the shoulder first. Both the biceps brachii and the triceps brachii are multijoint muscles that are developing force at various phases in this movement. The long head of the triceps brachii crosses the shoulder and the elbow joint, causing extension of the both joints. However, when the shoulder is extending in the movement, the elbow is extending as well, so there is not an “unwanted” action created by this muscle. This same situation is true for the biceps brachii in some phases of the skill. The biceps brachii crosses the elbow, shoulder, and radioulnar joint, causing flexion, flexion, and supination, respectively. During the early countermovement, the shoulder and elbow flex simultaneously so no neutralization is needed for those movements. However, the forearm is maintained in a neutral position throughout the skill, so if the biceps brachii is developing force, then its supination movement must be neutralized. This neutralization may be accomplished by the pronator quadratus or the pronator teres. Also, in the execution phase, flexion of the shoulder is occurring, but the elbow maintains an extended position. Therefore, if the biceps brachii is developing force, then the flexion at the elbow must be neutralized. This neutralization is probably performed by the anconeus, since force development in the triceps brachii would counteract the shoulder flexion movement. Of course, the other alternative is that body does not recruit the biceps brachii at all and simply uses other movers as appropriate at the joints. Other examples of neutralization under this scenario may be occurring in the lower extremity as well, since many of those muscles are multijoint muscles (sartorius, gracilis, semimembranosus, semitendinosus, biceps femoris – long head, rectus femoris, gastrocnemius). Can you identify any of these examples?

• Is the humerus being elevated in this movement so that stabilization of the humerus by the rotator cuff would be necessary? Yes, during the execution phase. The rotator cuff must develop force to stabilize the humeral head against the superior shear created by contraction of the deltoid muscle.

• Other? Are there any other undesired actions of the agonists that need to be neutralized? Well, if we list all the actions of the active FMGs during each phase, we are able to examine this further. There are numerous possibilities here since movement is occurring at most of the joints in the body. Let’s just identify one case as an example. At the shoulder, the anterior deltoid is part of the active FMG in several phases of the skill. When the anterior deltoid contracts, not only does it attempt to flex the shoulder but it also causes medial rotation. Since medial rotation does not occur during this skill, then that action must be neutralized by at least one other muscle. None of the other muscles in the shoulder flexor FMG are lateral rotators, so there is no synergistic action within the FMG. Therefore, the likely source of neutralization is a lateral rotator. There are several possibilities. The posterior deltoid could neutralize the medial rotation but since it is antagonistic to the flexion being caused by the anterior deltoid, it is not a likely candidate. Two other lateral rotators are the infraspinatus and the teres minor. We have already identified these rotator cuff muscles as being recruited to stabilize the humeral head against the superior pull of the deltoid, so these muscles are likely candidates for neutralization of medial rotation. Can you identify other examples of neutralization at other joints under this scenario?

d. Are there any potential force production problems in the movement related to the force-length relationship (you should especially consider multi-joint muscles)? How can the performer overcome these problems or is the performance limited by these problems? Explain your answer.

If we examine the multijoint muscles developing force, there does not appear to be a situation where one of the multijoint muscles is placed in an extremely short or extremely long position. For example, in the lower extremity, there are several multijoint muscles developing force. The hamstring group is the active FMG throughout the movement, both eccentrically and concentrically. However, when that muscle group is lengthened across the knee, it is shortened across the hip, avoiding an extremely long or short position that would place it in a disadvantageous position on the force-length curve. An analysis of most of the multijoint muscles in the lower extremity would produce the same result. You might identify one exception in the sartorius, which is a knee flexor and a hip flexor. When the hip and knee are flexed simultaneously as occurs at the bottom of the countermovement, then the sartorius is in a very short position. However, the hip flexors and the knee flexors are not developing force at this point in the movement, so there is not a force output problem.

2. Complete a muscular analysis of the push-up exercise under two conditions – one with hands placed greater than shoulder width apart, and one with hands placed just less than shoulder width apart (keeping the elbows in). Use the questions below to help you with your analysis.

a. Complete the charts below for each exercise.

|Wide Hand Placement |

| |Down Phase |Up Phase |

|Joint |Shoulder |Elbow |Shoulder |Elbow |

|Joint Action |horizontal abduction |flexion |horizontal adduction |extension |

|Motive Torque |weight |weight |muscle |muscle |

|Resistive Torque |muscle |muscle |weight |weight |

|Muscle Action |eccentric |eccentric |concentric |concentric |

|FMG Developing Force |horizontal adductors |extensors |horizontal adductors |extensors |

|Agonists (FMG) |horizontal abductors |flexors |horizontal adductors |extensors |

|Antagonists (FMG) |horizontal adductors |extensors |horizontal abductors |flexors |

|Narrow Hand Placement |

| |Down Phase |Up Phase |

|Joint |Shoulder |Elbow |Shoulder |Elbow |

|Joint Action |extension |flexion |flexion |extension |

|Motive Torque |weight |weight |muscle |muscle |

|Resistive Torque |muscle |muscle |weight |weight |

|Muscle Action |eccentric |eccentric |concentric |concentric |

|FMG Developing Force |flexors |extensors |flexors |extensors |

|Agonists (FMG) |extensors |flexors |flexors |extensors |

|Antagonists (FMG) |flexors |extensors |extensors |flexors |

a. Compare and contrast the ROMs used at the shoulder and elbow joints in the two exercises. Are there any force-length effects that cause muscle involvement to be different between the primary muscle groups in the two exercises?

ROM of the elbow is very different between the two exercises. The working ROM in the wide hand placement is 0-90°, while the working ROM in the narrow hand placement is 0-140°. Since the elbow extensors are the active FMG in both of these exercises, then we should examine force-length effects of these muscle (the anconeus and the triceps brachii). Let’s focus on the triceps brachii since it is the major force producer in this group. During the wide hand placement exercise, the medial and lateral heads of the triceps brachii are extremely short at the top of the movement when the elbow is fully extended (0°), limiting force production in these heads. However, the long head is not compromised in this position because even though it is shortened across the elbow, it is placed in a lengthened position across the shoulder, placing it in a fairly optimal position on the force-length curve. At the bottom of the movement, none of the triceps heads are compromised as the elbow joint angle is approximately 90°, or in the midpoint in the ROM, again placing it in an optimal position on the force-length curve.

In the narrow hand placement exercise, the same is true for the top of the movement as we described in the wide hand placement. However, at the bottom of the movement, all three heads of the triceps are in an extremely lengthened position, compromising their force output due to their length. The long head does not reach its maximal length since the shoulder is not completely hyperextended, which would actually be advantageous since it is a multijoint muscle. Therefore, at the bottom of the movement when concentric force is necessary to raise the body, the triceps brachii force output is compromised, making this exercise much more difficult with respect to the elbow extension portion.

b. For each exercise, identify two examples in which rotary stabilization is performed by muscles. Compare and contrast this stabilization between exercises.

Rotary stabilization occurs at several joints in this skill, because most of the segments are not moving and yet muscular torque is necessary to keep them from rotating. Examples of rotary and linear stabilization are described below. In each bullet, a specific scenario is examined as we identified in lecture.

• Rotary stabilization by muscles often occurs at joints in which no rotation is occurring. This case is usually the simplest case of rotary stabilization to identify. You should ask whether the lack of movement (rotation) at a joint is because there are no forces acting to rotate the joint, or because two or more forces are acting in such a way that the net torque is zero, and rotation does not occur. If the latter, and if muscle is one or both of the forces acting, then muscles are acting as rotary stabilizers. Three examples of this case are identified below:

o Hyperextension of the lumbar and thoracic trunk tends to occur due to the force of gravity. The trunk flexors must contract to prevent this hyperextension.

o Flexion of the knee tends to occur due to the force of gravity. The knee extensors must contract to prevent this flexion.

o Dorsiflexion of the ankle tends to occur due to the force of gravity. The ankle plantar flexors must contract to prevent this dorsiflexion.

• Rotary stabilization also occurs when a multijoint muscle in the agonist or antagonist FMG is developing force that may be causing unwanted action at adjacent joints. Let’s look at the wide hand placement push-up first. The FMGs for this exercise include the horizontal adductors and the elbow extensors. The only multijoint muscle in those FMGs is the triceps brachi, which is an elbow extensor. The long head of the triceps brachii crosses the shoulder and the elbow joint, causing extension of the both joints. While elbow is extension is desired in the movement, shoulder extension is not. So, the shoulder extension must be offset so that the shoulder does not move (is stabilized). This stabilization is easily accomplished by any of the agonist horizontal adductors, all of which are shoulder flexors as well. Therefore, the agonists stabilize against the unwanted shoulder extension of the triceps brachii. The same is true in the narrow hand placement push-up. The shoulder flexors stabilize against the shoulder extension created by the triceps brachii-long head.

• Linear stabilization occurs when the scapula or pelvis has to be stabilized to provide a firm base from which muscles that move the femur and humerus can pull. In these exercises, the muscles that cause horizontal adduction (anterior deltoid, pectoralis major, coracobrachialis) during the wide hand placement push-up attach to the scapula/clavicle and would tend to cause shoulder girdle protraction, so it appears that the scapula would need to be stabilized against the pull of these agonist muscles. However, it is important to recognize that movement of the shoulder girdle (protraction) must occur to accompany and facilitate the horizontal adduction of the shoulder. So, technically, there is no stabilization of the scapula (the scapula is not fixed in place), but instead, this is considered a dynamic stabilization that occurs in the shoulder girdle. The concept of dynamic stabilization is beyond the scope of this course at this time. It is important that you recognize that technically, there is no scapular stabilization as we have defined stabilization (fixation). The same concept (dynamic stabilization) holds true for the narrow hand placement push-up.

• Linear stabilization also occurs when the humerus is being elevated in a movement. In this movement, stabilization of the humerus by the rotator cuff would be necessary.In both exercises, the rotator cuff must develop force to stabilize the humeral head against the superior shear created by contraction of the anterior deltoid muscle, which is a member of the FMGs in both exercises.

These examples of stabilization occur in both exercises. Stabilization does not differ across the two exercises.

c. For each exercise, identify two examples in which neutralization is performed by muscles. Compare and contrast this neutralization between exercises.

To examine neutralization, you should ask whether there are any undesired actions of the agonists that need to be offset. Well, if we list all the actions of the active FMGs during each phase, we are able to examine this further. For the elbow, the only unwanted action of the individual muscles in the FMGs (triceps brachii and anconeus) is the shoulder extension that we have already discussed. At the shoulder, the anterior deltoid and the pectoralis major are also medial rotators. However, in the wide grip hand placement, the position of the humerus is already medially rotated to some extent, and, therefore, the line of pull for the pectoralis major is direct and does not create a medial rotation torque. The line of pull for the anterior deltoid may produce a slight medial rotation torque, but this torque is easily neutralized by the two of the rotator cuff muscles (teres minor and infraspinatus) which produce a lateral rotation torque. In the narrow grip hand placement, the humerus is not medially rotated, therefore, the line of pull of the anterior deltoid and pectoralis major-clavicular is not direct and exerts a medial rotation torque at the shoulder. This medial rotation must be neutralized, and again, the only lateral rotators that are candidates are the infraspinatus and the teres minor. The posterior deltoid is a lateral rotator, but it is not recruited since it would act antagonistic to the anterior deltoid. Therefore, rotator cuff strength is another requirement for performance of the narrow hand placement push-up. Weakness in these muscles is one reason people perform this exercise incorrectly, with the shoulder medially rotated and the elbow pointed at to the sides

d. Given your answer to ‘c’, are there any individual muscles in the FMG that you identified in the chart that would not necessarily be involved in the performance of this exercise?

The biceps brachii is probably not recruited as a shoulder flexor in the narrow push-up since it is antagonistic to the elbow extensors. One could also argue that the long head of the triceps brachii may not be as active in these exercises, since it has an undesirable action at the shoulder. A more sophisticated, quantitative analysis would need to be done to determine whether this is true or not.

e. Use the chart and your answers to the questions above to summarize the muscle involvement in the two exercises. Note where they are similar and where they are different.

The primary difference between these exercises is in the shoulder joint actions and active shoulder FMGs. In the wide hand placement, the shoulder FMG is the horizontal adductors, which includes the pectoralis major, the anterior deltoid, and the coracobrachialis. In the narrow hand placement, the shoulder FMG is the flexors, which includes the pectoralis major-clavicular, the anterior deltoid, and the coracobrachialis. The rotator cuff muscles probably play a more important role in the narrow push-up, and the strength requirements of triceps brachii are demanded throughout the entire elbow ROM in the narrow push-up as compared to the wide push up.

f. The narrow hand width position is considered to be more difficult than the wide hand width position. Based on your analysis, can you support this statement?

Yes. The narrow hand placement exercise is more difficult for three reasons. First, the shoulder flexion movement is not as strong a movement as the shoulder horizontal adduction movement simply because there is not as much active muscle mass in the shoulder flexors. The shoulder horizontal adductors include the pectoralis major – sternal portion which is a large muscle capable of producing a large amount of force. This muscle is not part of the shoulder flexor FMG, making this a much weaker movement. Second, in the narrow hand placement exercise, the triceps brachii force production is severely compromised at the bottom of the movement when the muscles must act concentrically to raise the body. This compromise occurs because of the large ROM at the elbow which places the muscle in a poor position on the force-length curve. This does not occur in the wide hand placement exercise. Third, the rotator cuff muscles, especially the infraspinatus and the teres minor, appear to play a more significant role in the narrow push-up. They must neutralize the medial rotation of the humerus caused by the agonists during shoulder flexion, and they must neutralize against the superior shear created by the shoulder agonists as well. Since these muscles are small, the increased torque demand of the exercise makes strength in these muscles very important. The first two factors result in a much lower muscle torque output during the narrow hand placement exercise, making it much more difficult, since the resistance (body weight) is the same in both exercises. The increased torque demand on the relatively small muscles of the infraspinatus and teres minor also makes the narrow hand placement exercise more difficult.

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