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The purpose of this study was to determine the extent to which high frequency, low amplitude skeletal muscle contractions, induced using electrical stimulation, could prevent or retard disuse osteopenia. Ten minutes of 30 Hz electrical stimulation was delivered, 5 days a week, during a 4 week rat-hindlimb suspension protocol. Each pulse generated a peak compressive dynamic strain on the tibia of approximately 200 μɛ. We hypothesized that the electrical stimulation protocol would significantly reduce the loss of tibial bone mineral density compared to the contralateral control tibia that did not receive electrical stimulation. Compared to the contralateral control limb, the tibia of the stimulated limb had significantly higher bone mineral density and enhanced newly formed bone in the tibial diaphysis. The diaphysis, specifically the posterior bone cortex, of the tibia of the limb receiving the stimulation also demonstrated substantially larger mineral-binding fluorochrome biomarker within the osteocyte lacunae and canalicular volumes. Although the protocol did not prevent disuse osteopenia the evidence suggests that it was effective at reducing the extent of the osteopenia. One possibility for this outcome may be the insensitivity of bone to static, compared to dynamic compressive loads. In the present study there was a considerable static component to the compressive loads that accounted for a large component of the peak load generated by the stimulated skeletal muscle. Nevertheless, the results provide impetus for further development of the methods by which muscle contraction-induced loading of bone can be clinically exploited.

The rehabilitation of chondral injuries and degenerative knees is challenging. Setting short- and long-term goals enables the athlete to cope with the psychology of injury while facilitating a return to sport. Rehabilitation must be gradual, progressive, and goal oriented for each individual. Protocols must include range of motion, flexibility exercises, strength training, and cross training. Compliance with all aspects off the program is important and the athlete must have direct communication with the therapist via telephone conversation and/or personal appointments. Carefully guided rehabilitation affords athletes the means necessary to regain functional use of the limb while promoting dynamic unloading of injured articular cartilage.

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 com pressive force was produced. Inability to generate suf ficient elbow varus torque may result in medial tension, lateral compression, or posteromedial impingement in jury. 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 gener ated at the shoulder; contribution of rotator cuff muscles in generating these loads may result in cuff tensile fail ure. Horizontal adduction, internal rotation, and superior translation of the abducted humerus may cause sub acromial impingement. Tension in the biceps tendon, due to muscle contraction for both elbow flexion torque and shoulder compressive force, may tear the antero superior labrum.

Confusion of the terms open and closed kinetic chain and scarcity of research comparing kinetic chain exercises that have similar mechanics and loading prompted this case study. Exercises were classified by the boundary condition of the distal segment and presence of an external load. Classifications included a fixed boundary condition with an external load (FEL), a movable boundary with an external load (MEL), and a movable boundary with no external load (MNL). It was hypothesized that if the direction and mass of loading in MEL and FEL exercises were similar, the electromyographic activity of the primary muscle groups involved would be comparable. Muscular activity was monitored from six shoulder muscles during one MNL, four MEL, and five FEL exercises. The results indicated that MEL and FEL exercises having similar biomechanics produced comparable muscular activity. Evaluation and selection of exercises for patients should be based upon mechanics and loading that achieve appropriate muscle activity.

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.

Common aspects are involved in a variety of throwing motions. During most throwing activities, the elbow is stressed to its biomechanical limits. Through proper coordination with the rest of the body, the muscles about the elbow joint generate the rapid extension, flexion, pronation, and supination needed for sport performance. Hard and soft joint tissue are loaded to capacity to generate and control these rapid motions. These loads may include large tensile forces on medial soft tissue (e.g., UCL), large compressive forces on lateral hard tissue (e.g., radiocapitellar articulation), soft tissue tensile loads to prevent joint distraction, and hard tissue loads to withstand compression and varus and valgus torques.

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.

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.

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 flexor-pronator, 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.

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.

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.

An analytical model of tennis impact was derived in an attempt to describe how the angle of swing and the orientation of the racket head act to impart spin to a tennis ball. For years, coaches and instructors have debated on the contribution of each parameter to spin production. The specific purpose of this investigation was to formulate a theoretical model of impact to examine the importance of various factors involved and how each contributes to the outcome of the tennis impact. Given the pre‐impact parameters from cinematographic data, the post‐impact ball rotation values were determined. The calculated values of ball spin following impact in eight experimental trials were compared with their theoretically determined values. The data suggests that the analytical model may be a good representation of tennis impact and the production of ball spin.

The purpose of this study was to determine if the cubic spline could provide accurate smoothed estimates of displacement-time functions and corresponding time derivatives for typical biomechanical data obtained from cinematographical records. Various experiments were conducted to ascertain a procedure for determining the error associated with data and for validating and comparing results obtained by the cubic spline with other commonly employed curve-fitting techniques. Results of these experiments indicated that reasonable estimates of the error inherent in the data can be assessed a priori, and, when used in conjunction with the cubic spline, an accurate description of displacement-time data and corresponding time derivatives can be obtained. Since the cubic spline has the natural tendency to approach zero at the endpoints of a function for the second derivatives, special consideration should be taken in applying the cubic spline when second derivatives at the endpoints are unknown or not equal...

A method for measuring the forces between the shoe and ski and upon the pole has been developed. Instrumented skis and poles are used with a portable data acquisition system that is carried by the skier in the field. Elite, top-level collegiate, and citizen skiers were used as subjects. Skiers performed the diagonal stride, and a marathon skate. Axial force levels at the forefoot were found to reach 164%, and 120% of body weight in the diagonal skate strides, respectively.

The purpose of this project is to describe the procedures used in acquiring data on the Men's Olympic Long Horse Vaulting Competition. A descriptive biomechanical analysis is provided of the filmed performances of the eight male finalists in this event. All of the performed vaults are grouped into the following two vault families: Handspring Front Somersault and Tsukahara. Comprehensive kinematic descriptions are presented for these two vault families.

The mission of the Sports Biomechanics Laboratory at the Olympic Complex is to conduct mechanical evaluations of various events and to make judgments as to how these factors influence the performance of athletes who are in training for the Olympics. Evaluation is made using high speed film that is analyzed frame by frame on a computerized digitizing system.

(1980). Guidelines and Standards for Undergraduate Kinesiology. Journal of Physical Education and Recreation: Vol. 51, No. 2, pp. 19-21.

The purpose of this study was to determine the relative changes in kinetic and potential energy which occurred during the performance of vaults with a fiberglass pole. A 16mm camera was used to film four college pole vaulters during practice over a four-week period. Measurements were made of nine segmental centers of gravity and pole bend from every fifth frame of the best four vaults by each subject. A computer program was developed to calculate from these basic data the following biomechanical components: The vaulter's center of gravity (segmental method), vertical and horizontal velocities, kinetic and potential energies, predicted height, adjusted predicted height, actual height, and vertical energy gained. The decrease in kinetic energy and the increase in potential energy occur at different rates during the vault. The fiberglass pole provides an effective means of transforming kinetic energy to potential energy throughout the vault. Vaulters achieve certain heights by distributing the losses in kinetic energy and gains in potential energy in specific energy patterns.

The biomechanics of overground and treadmill running were compared using cinematographic methods. Sixteen experienced runners were filmed while running at three speeds and on three slopes over both surfaces. Temporal factors and vertical and horizontal velocities of the center of gravity wer