Diane R. Moynes

Dynamic electromyographic analysis of the throwing shoulder with glenohumeral instability

Fifteen male athletes who were skilled in throwing and who had chronic anterior instability of the shoulder (Group 1) were evaluated by dynamic intramuscular electromyography while pitching a baseball. Indwelling wire electrodes recorded the levels of activity in the biceps, middle deltoid, supraspinatus, infraspinatus, pectoralis major, subscapularis, latissimus dorsi, and serratus anterior throughout the entire pitching sequence. These signals were synchronized electronically with records of the pitch that were made using high-speed photography. The pitch was divided into five phases: wind-up, early cocking, late cocking, acceleration, and follow-through. The results were compared with previous identical studies of twelve healthy, uninjured male athletes who were skilled in throwing (Group 2). Activity increased mildly in the biceps and supraspinatus in Group 1 as compared with Group 2. Similar patterns of activity were demonstrated in the deltoid. In Group 1 the infraspinatus had increased activity during early cocking and follow-through but had decreased activity during late cocking. The pectoralis major, subscapularis, latissimus dorsi, and serratus anterior in Group 1 all were shown to have markedly decreased activity. The study revealed a difference between Groups 1 and 2 in all of the muscles of the shoulder that were tested with the exception of the deltoid. The mildly increased activity levels of the biceps and supraspinatus that were found in Group 1 may compensate for anterior laxity. The marked reduction in activity in the pectoralis major, subscapularis, and latissimus dorsi added to the anterior instability by decreasing the normal internal-rotation force that is needed during the phases of late cocking and acceleration.(ABSTRACT TRUNCATED AT 250 WORDS)

An EMG analysis of the shoulder in pitching A second report

This is the second report in a series of projects dealing with electromyographic (EMG) analysis of the upper extremity during throwing. Better understanding of the muscle activation patterns could lead to more effective preseason conditioning regimens and rehabilitation pro grams. Indwelling wire electrodes recorded the output from the biceps, long and lateral heads of the triceps, pectoralis major, latissimus dorsi, serratus anterior, and brachialis for four professional baseball pitchers. These signals were synchronized electronically with high speed film records of a fast ball. The EMG signals were converted from analog to digital records. Results showed that wind-up and early cocking phases showed minimal activity in all muscles, and such firing which occurred was of low intensity. Late cocking, which occurred after the front foot was firmly planted, showed moderate activity in the biceps. Cocking was termi nated by the pectoralis major and latissimus dorsi. At this point, the trunk began to rotate forward, while the arm remained elevated and the elbow flexed. Also, the shoulder was moving to maximum external rotation. During the acceleration phase, the biceps was notably quiescent, while the pectoralis major, latissimus dorsi, triceps, and serratus anterior were all active. Muscle action at this time terminated external rotation and elbow flexion; i.e., the muscles fired as decelerators and also initiated the opposite actions for ball acceler ation, internal rotation and elbow extension. Follow- through was not only a time of eccentric contraction with muscle activity decelerating the upper extremity complex, it was also an active event with the shoulder moving across the body and the elbow into extension with forearm pronation.

Delineation of diagnostic criteria and a rehabilitation program for rotator cuff injuries

In the examination and rehabilitation of patients with shoulder injuries it is necessary to isolate the individ ual rotator cuff muscles as much as possible. We subscribe to the belief that, independent of the deltoid, the rotator cuff muscles can become fatigued, injured, or atrophied individually. Accordingly, we feel that these muscles must be considered separately during examination and rehabilitation. This paper describes methods and positions to iso late the cuff and, thus, enable the examiner to be more precise in diagnosis and treatment. In addition, individual exercises for each component are de scribed.

A comparative electromyographic analysis of the shoulder during pitching: Professional versus amateur pitchers

Dynamic, fine-wire, intramuscular electromyography (EMG) was performed on 12 different shoulder muscles in 13 normal male subjects as they pitched a baseball. Seven were major league baseball pitchers and six were amateur pitchers. The act of pitching a fast ball was filmed at 450 frames per second with the EMG signals recorded synchronously. The subscapularis, su praspinatus, and infraspinatus muscles were tested in 13 subjects, the biceps brachii muscle was tested in 12, and other shoulder muscles were tested variously among the subjects. Two groups of muscles were identified. Group I mus cles, the supraspinatus, infraspinatus, teres minor, del toid, trapezius, and biceps brachii, served primarily to position the shoulder and elbow for the delivery of the pitch. These muscles were found to have greater activ ity during the early and late cocking stages, with less activity during acceleration. Group II muscles acceler ated the arm and baseball forward in space. These muscles, the pectoralis major, serratus anterior, sub scapularis, and latissimus dorsi, had stronger activity during the propulsive phase of the pitch. The professional pitchers were able to use the mus cles about the shoulder in an efficient manner to achieve greater pitching velocities. The subscapularis and latis simus dorsi muscles of Group II had stronger activity among the professionals, whereas the supraspinatus, teres minor, and biceps brachii muscles of Group I had only minimal activity. The amateurs, on the other hand, continued to use all of the rotator cuff muscles and the biceps brachii muscle of Group I through the accelera tion stage of the pitch. These data may provide a basis for understanding improved performance and an ad junct for sport-specific rehabilitation programs.

Functional analysis of anterior cruciate ligament instability

Eighteen males and two females (mean age, 26.5 years) underwent biomechanical assessment and Cybex eval uation prior to ACL reconstruction. Clinically, all patients had at least a 1+ grade with the Lachman, anterior drawer, and pivot shift tests, the majority being graded as 2+. Footswitch, high speed photography, force plate, and indwelling wire electrode data were collected while each subject performed free and fast walking, running, cutting, and stair climbing activities. During walking, single limb support times did not differ between the subjects involved and uninvolved limbs. Knee joint angles were similar between limbs during walking, running, and stair climbing maneuvers. Dynamic EMG tracings during walking demonstrated similar quadriceps and calf activity between limbs, while greater variation in hamstring firing was evident among subjects. During running, the involved limb had a longer duration of medial hamstring activity compared to the lateral hamstring. No significant differences were seen in either vertical or sagittal shear forces during free walking. During fast walking, higher midstance vertical forces (F2) were present in the involved limb (P < 0.05). During running, the involved limb experienced lower vertical forces (P < 0.05), while both anterior and posterior sagittal shear differences were insignificant. Straight cut maneuvers demonstrated significantly lower lateral shear and ver tical forces in the involved limb (P < 0.05). Lower lateral and sagittal shear forces in the involved limb (P < 0.01 and P < 0.05, respectively), combined with a reduced angle of the cut during the cross-cut maneuver, may be the first means to assess the functional pivot shift phenomenon ever documented. Isokinetic Cybex strength testing demonstrated a mean 14% quadriceps deficit and a mean 4% hamstring deficit in the involved limb. Achieving quadriceps and hamstring torque of 86% and 96%, respectively, was not sufficient to eliminate the subjective need for sur gical reconstruction.

An electromyographic analysis of shoulder function in tennis players

Shoulder injuries in tennis players are common because of the repetitive, high-magnitude forces generated around the shoulder during the various tennis strokes. An understanding of the complex sequences of muscle activity in this area may help reduce injury, enhance performance, and assist the rapid rehabilitation of the injured athlete. The supraspinatus, infraspinatus, subscapularis, mid dle deltoid, pectoralis major, latissimus dorsi, biceps brachii, and serratus anterior muscles were studied in six uninjured male Division II collegiate tennis players using dynamic electromyography (EMG) and synchro nized high-speed photography. Each subject performed the tennis serve and the forehand and backhand groundstrokes, and each stroke was divided into stages. The tennis serve contains four stages. Three stages characterize the forehand and backhand ground strokes. Our results indicate that the subscapularis, pectoralis major, and serratus anterior display the greatest activity during the serve and forehand. The middle deltoid, supraspinatus, and infraspinatus are most active in the acceleration and follow-through stages of the backhand. The biceps brachii increases its activity during cocking and follow-through in the serve with a similar pattern noted in the acceleration and follow-through stages of the forehand and back hand. The serratus anterior demonstrates intense activ ity in the serve and forehand, thus providing a stable platform for the humeral head and assisting in gleno humeral-scapulothoracic synchrony. The tennis serve and forehand and backhand ground strokes are accomplished by complex sequences of muscle activity that incorporate contributions from the lower extremities and trunk into smooth, coordinated patterns. Although our study focused on shoulder function in the uninjured tennis player, it may provide a basis for understanding abnormal shoulder biomechanics that contribute to pain and dysfunction. The serratus anterior deserves special emphasis, for our study showed that its activity is essential to each of the three tennis strokes. Because of the similarities between the tennis serve and overhead throw, a conditioning program comparable to one pitchers use many be appropriate for tennis players.

An electromyographic analysis of the elbow in pitching

Elbow injuries are common in baseball pitchers. Curve balls are thought to increase this risk, particularly if the athlete begins throwing this pitch at an early age. The purpose of this paper is to identify forearm muscle firing patterns during the pitching cycle in an effort to under stand this etiology. Dynamic EMG was performed on eight collegiate pitchers to evaluate extensor digitorum communis, brachioradialis, flexor carpi radialis, flexor digitorum superficialis, extensor carpi radialis longus, extensor carpi radialis brevis, pronator teres, and supinator. Each subject threw a fast ball and curve ball, which were filmed at 450 frames per second and synchronized with the EMG. These signals were converted from analog to digital records. Results showed low to moderate activity in all muscles during all phases of the pitch. The function is probably positioning to accept the transfer of energy from the larger trunk and girdle structures. The most notable difference between the fast ball and curve ball is a slight increase in the extensor carpi radialis longus and extensor carpi radialis brevis activity during late cocking, acceleration, and follow-through of the curve ball as compared to the fast ball. This differ ence, however, is not significant. In addition, there was no significant difference between the fast ball and the curve ball in the flexor-pronator group in any phase. We cannot substantiate that medial elbow problems are a result of an increase in the use of flexor muscles during the curve ball pitch.

Fine wire electromyography analysis of muscles of the shoulder during swimming

Fine wire EMG of the shoulder was performed on 11 swimmers; 5 performed during dry land studies and 7 during aquatic studies. One individual underwent both studies. A cinematographic analysis was synchronized with the EMG data to determine what muscles were firing at each phase of the swim stroke. Eight muscles were studied: biceps, subscapularis, latissimus dorsi, pectoralis major, supraspinatus, infraspinatus, serratus anterior, and deltoid. Three stokes were analyzed: freestyle, breaststroke, and butterfly. The freestyle and butterfly are frequently associated with impingement type syndromes in swimmers. It was determined that the supraspinatus, infraspi natus, middle deltoid, and serratus anterior were pre dominately recovery phase muscles. The latissimus dorsi and pectoralis major were predominately pull- through phase muscles. The biceps had mixed incon sistent activity during both phases. From dry land quan tifications of the EMG signal it was determined that the serratus anterior functions near maximal muscle test during each stroke, and theoretically may fatigue with repetition. It is hoped that a training program aimed to strengthen the scapular rotators may help alleviate impingement syndrome in swimmers.

Essential statistics review

As medicine and science have become more sophis ticated, so too have the research designs, data collec tion, and statistical analyses employed by medical investigators. This paper is a review of some of the basic terminology and procedures essential in evalu ating research results.

Elbow flexion analysis in Bristow patients A preliminary report

Seven male nonathletes who had Bristow procedures for shoulder dislocation were analyzed by dynamic electromyography (EMG) and Cybex strength measure ment to evaluate the function of elbow flexion. Bilateral strength of elbow flexion also was measured in the 10 controlled subjects to compare the dominant and non- dominant arms. The EMG data showed the operated short head of biceps function at low constant intensity, compared with the nonoperated side, while the long head of biceps and brachialis increased their activity. The strength measured by the Cybex demonstrated the elbow flexion on the operated side was not signifi cantly different from the normal group. These data demonstrated that the Bristow procedure reduced the dynamic response of the short biceps which was com pensated for by the increase in level of activity of the long heads and brachialis muscle. As a result, normal range of elbow function was restored. Our patients had had intense rehabilitation programs. This appears to be an essential part of the postoperative management to develop the needed compensatory muscle action.