Quantification of elastic resistance knee rehabilitation exercises.

Elastic resistance exercises are frequently used for knee rehabilitation following injury and/or surgery. The evidence supporting this mode of rehabilitation is primarily anecdotal, and no biomechanical assessment of elastic resistance exercises has been previously published. The purpose of this project was to quantify muscle activation levels, knee joint angles, and applied force during five rehabilitation exercises utilizing an elastic resistance device. Twelve subjects with no previous knee injury performed double knee dip, hamstring pull, leg press, single knee dip, and side-to-side jump exercises while sagittal plane kinematics, applied force from the elastic resistance device, and electromyographic activity of eight lower extremity muscles were collected. The muscle activation patterns suggest a progressive continuum of rehabilitation exercises that can be applied to nonoperative injuries as well as anterior cruciate ligament reconstructions.

Muscle activity in wedge, parallel, and giant slalom skiing.

Muscle activity patterns of six alpine skiers were compared during nine runs each of wedge (W), short radius parallel (P), and giant slalom (GS) turns. Bipolar surface electrodes were placed over 12 muscles on the right side of the body: anterior tibialis, medial gastrocnemius, vastus medialis, vastus lateralis, rectus femoris, medial hamstrings, biceps femoris, gluteus maximus, adductors, rectus abdominis, external obliques, and erector spinae. Repeated measures ANOVA was used to test for differences in average and peak EMG amplitudes between W, P, and GS (P < 0.1). Average amplitude was significantly different between all turning styles (W < P < GS) for four muscles (vastus lateralis, medial hamstrings, biceps femoris, and external obliques) and significantly less for W versus P or GS for four muscles (anterior tibialis, vastus medialis, rectus femoris, and rectus abdominis). The gluteus maximus was the only muscle that had significantly greater activity in W than P. Average amplitude was greater than 50% MVC for the vastus medialis, vastus lateralis, biceps femoris, gluteus maximus, and adductors in all conditions; and for the anterior tibialis, medial hamstrings, and rectus femoris in GS and P; and for the medial gastrocnemius and erector spinae in GS. Peak amplitude was greater than 150% maximal voluntary contraction (MVC) for the vastus medialis, vastus lateralis, biceps femoris, gluteus maximus, and adductors in all conditions, and for the medial gastrocnemius, rectus femoris, and erector spinae in GS. This research indicates that with the exception of the gluteus maximus, greater muscle activity is required in GS followed by P and W turns.

Electromyographic and kinematic analysis of graded treadmill walking and the implications for knee rehabilitation.

Muscle activity, joints, angles, and heart rate during uphill walking were compared for application in knee rehabilitation. The objectives of this study were to quantify muscle activation levels at different treadmill grades and to determine the grade(s) at which knee range of motion would not further compromise the joint. Average and peak electromyographic activity of the quadriceps (vastus medialis oblique and vastus lateralis) and hamstrings (biceps femoris and medial hamstrings (semimembranosus/semitendinosus)] was recorded during walking at 0, 12, and 24% grade. Six subjects (age = 28.5 +/- 3.7 years, stature = 1.79 +/- .05 m, and mass = 74.7 +/- 7.9 kg) walked at self-selected speeds at each grade while ankle, knee and hip angles, heart rate, and electromyographic activity (surface electrodes) were recorded. Maximum voluntary contractions provided a relative reference for the electromyographic activity during walking. Average and peak electromyographic activity increased significantly across grades for the vastus medialis oblique (125 and 154%), vastus lateralis (109 and 139%), and biceps femoris (53 and 46%), but remained similar for the medial hamstrings. Maximum knee flexion at heel strike increased significantly with grade. Despite decreased self-selected speeds with increasing grade, there were significant increases in heart rate across grades. The results of this study provide a basic understanding of the quadriceps and hamstrings activity levels, lower extremity joint range of motion, and cardiovascular requirements of graded treadmill walking in normal subjects. The results also suggest that a grade just greater than 12% may be most beneficial for knee rehabilitation to minimize patellofemoral discomfort or potential strain on the anterior cruciate ligament. The benefits achieved through this functional activity encourage its implementation in rehabilitation and provide a basis for comparison with injured patients.

Rehabilitation of the shoulder.

Rehabilitation of the shoulder has undergone significant changes during the past few years due to many clinical and basic science projects that have taught us about biomechanics of the shoulder. The athlete's shoulder is a particularly good model to allow us an understanding related to rehabilitation for treatment of injuries, injury prevention and performance enhancement. A comprehensive rehabilitation program for athletes can be based on these clinical and basic science principles to aid in our understanding of rehabilitation for shoulders in general.

Muscle activity in slalom and giant slalom skiing.

The purpose of this study was to document and compare the muscular activity patterns observed in seven competitive racers during slalom (SL) and giant slalom (GS) skiing using quantitative parameters of EMG and qualitative video recordings. Twelve muscles of the leg and trunk were monitored using surface electrodes and telemetry. EMG activity was related to phases of movement determined from the video. SL was partitioned into two phases (initiation and turning) and a third phase (completion) was distinguished for GS. The majority of muscles were active at a moderate to high level for the whole turn, with average amplitudes (AA) between 58% and 112% maximum voluntary contraction. Large peak amplitudes (PA) were attributed to the substantial components of centrifugal and gravitational force that the skier must resist in the latter part of the turn. The similarity in muscle activity between SL and GS was surprising. The only significant differences were increases of 11.8% in AA for the AT in SL and 8.8% in PA for the EO in GS. There was ample evidence of co-contraction, suggesting a quasistatic component to skiing.

Kinetics of baseball pitching with implications about injury mechanisms.

Elbow and shoulder kinetics for 26 highly skilled, healthy adult pitchers were calculated using high-speed motion analysis. Two critical instants were 1) shortly before the arm reached maximum external rotation, when 67 N-m of shoulder internal rotation torque and 64 N-m of elbow varus torque were generated, and 2) shortly after ball release, when 1090 N of shoulder compressive force was produced. Inability to generate sufficient elbow varus torque may result in medial tension, lateral compression, or posteromedial impingement injury. At the glenohumeral joint, compressive force, joint laxity, and 380 N of anterior force during arm cocking can lead to anterior glenoid labral tear. Rapid internal rotation in combination with these forces can produce a grinding injury factor on the labrum. After ball release, 400 N of posterior force, 1090 N of compressive force, and 97 N-m of horizontal abduction torque are generated at the shoulder; contribution of rotator cuff muscles in generating these loads may result in cuff tensile failure. Horizontal adduction, internal rotation, and superior translation of the abducted humerus may cause subacromial impingement. Tension in the biceps tendon, due to muscle contraction for both elbow flexion torque and shoulder compressive force, may tear the anterosuperior labrum.

The biomechanics of tennis elbow. An integrated approach.

Tennis elbow afflicts 40% to 50% of the average, recreational tennis players; most of these players more than 30 years of age. Tennis elbow is thought to be the result of microtrauma, the overuse and inflammation at the origin of the ECRB as a result of repeated large impact forces created when the ball hits the racket in the backhand stroke. Several authors have found that EMG activity in the ECRB, the muscle and tendon complex afflicted in tennis elbow, is high during the acceleration and early follow-through phases of the groundstrokes and during the cocking phase of the serve. Unfortunately, none of the authors gave evidence to support the claim that muscle activity in the ECRB at ball contact is high. In the one-handed backhand, the torques at impact (17-24 nm) will be absorbed by the tendons of the elbow. Giangarra and his colleagues observed that the two-handed backhand "allows the forces at ball impact to be transmitted through the elbow rather than absorbed by the tissues at the elbow." Other authors have reported that players using a two-handed backhand will rarely develop lateral epicondylitis, because the helping arm appears to absorb more energy and changes the mechanics of the swing. As seen by Morris and colleagues, Giangarra and associates, and Leach and colleagues, players who utilize the two-handed backhand have a very low incidence of tennis elbow. These three studies conclude that the two-handed backhand stroke is probably the most effective backhand stroke to prevent lateral tennis elbow. Studies show that wrist extensors are highly involved in all strokes (serve, forehand, and both one- and two-handed backhand strokes). This relatively high involvement (40%-70% MVC) throughout play may result in overload of this muscular group. Thus, tennis elbow may be caused simply by continued use of this muscular system in all strokes, and not just because of the high forces absorbed at impact. Another theory concerning impact states that if the extensor group is already at near maximum contraction, vibrations and twisting movements are transferred directly through the muscle (muscle stiffness at this point would be great) to the tendinous insertion, causing repeated microtrauma. If the muscle is the stiffest element in the system, the force will be transferred to the tendon. It is evident that a need exists for specific study of muscular response during impact. More microanalysis of the impact phase needs to be conducted specifically for the one-handed backhand groundstroke.

Biomechanics of pitching with emphasis upon shoulder kinematics.

The American Sports Medicine Institute conducts research to increase understanding of mechanisms involved in upper extremity injuries to throwing athletes. This paper presents a qualitative overview of pitching and a detailed quantitative description of arm motion about the shoulder during this highly dynamic activity. Data on kinematics of arm motions about the shoulder are presented for 29 elite throwers. The major motion about the shoulder is external/internal rotation. Scapulothoracic and glenohumeral flexibility permit the arm to reach an externally rotated position of 175 degrees. Approximately 30 msec before release, the arm internally rotates 80 degrees, reaching peak angular velocities near 7,000 degrees/sec. In rehabilitation of injured throwers, there is a need to appreciate the highly dynamic nature of this skill and to attempt to simulate these dynamic motions and loads as part of the final phase of treatment before the athlete returns to competition.

Rehabilitation for the overhead athlete.

Rehabilitation of the shoulder of the overhead athlete has undergone significant changes during the past few years. This article illustrates shoulder problems related to repetitive overhead activities, such as throwing. Additionally, we present basic science contributions in this area, principles of shoulder rehabilitation, and a comprehensive rehabilitation program for the symptomatic or asymptomatic athlete based on these principles.

Biomechanics of the elbow during baseball pitching.

By understanding pitching biomechanics, therapists can develop better preventive and rehabilitative programs for pitchers. The purpose of this study was to quantify and explain the joint motions, loads, and muscle activity that occur at the elbow during baseball pitching. Seven healthy, adult pitchers were examined with synchronized high-speed video digitization and surface electromyography. Elbow extension before ball release corresponded with a decrease in biceps activity and an increase in triceps activity. A varus torque of 120 Nm, acting to resist valgus stress, occurred near the time of maximum shoulder external rotation. Previous cadaveric research showed that the ulnar collateral ligament by itself cannot withstand a valgus load of this magnitude. Triceps, wrist flexorpronator, and anconeus activity during peak valgus stress suggests that these muscles may act as dynamic stabilizers to assist the ulnar collateral ligament in preventing valgus extension overload.

Stretch-shortening drills for the upper extremities: theory and clinical application.

Enhanced athletic performance emphasizes the muscle's ability to exert maximal force output in a minimal amount of time. Exaggerated maximal muscular force develops due to athletic movements producing a repeated series of stretch-shortening cycles. The stretch-shortening cycle occurs when elastic loading, through an eccentric muscular contraction, is followed by a burst of concentric muscular contraction. A form of exercise called plyometrics employs a quick, powerful movement involving a prestretch of the muscle, followed by a shortening, concentric muscular contraction, thus utilizing the stretch-shortening muscular cycle. The literature contains numerous references to plyometric training for the lower extremity, but there is a lack of information on the upper extremity plyometric program. Overhead activities, such as throwing, necessitate elastic loading to produce maximal, explosive, concentric muscular contractions. Plyometric exercise employs the concept of the stretch-shortening muscular cycle. The rehabilitation concept of specificity of training suggests plyometric exercise drills should be performed by the throwing athlete. This paper discusses the basic neurophysiological science and theoretical basis for plyometric exercise, and it describes an upper extremity stretch-shortening exercise program for the throwing athlete.

Labral tears in throwing and racquet sports.

Throwing and overhead racquet motion is stressful activity that places great physical demands on the athlete's shoulder. This article focuses on glenoid labral tears as a consequence of this dynamic activity. These labral lesions may be present as an isolated entity or may be in association with glenohumeral instability.

Relationship between exposure time and injury in football.

This study investigated the relationship between exposure time and injury in football and the trends associated with these relationships. Data were collected at all practice sessions and games participated in by the University of Illinois varsity football team during the 1976 and 1977 seasons. Subjects consisted of the varsity football team at the University of Illinois. The 54 members of the traveling squad were the subjects used in the collection of game and injury data. Games were divided into three intervals and practice into five 25-min intervals in order to analyze the data. A likelihood ratio tests was used to test the data for statistical significance. An inverse relationship was found between exposure time and injuries for game data for both years. A curvilinear relationship, slightly skewed to the right, was found between exposure time and injuries for game data for both years. A curvilinear relationship, slightly skewed to the right, was found between exposure time and injury for the practice data for both seasons.