Study Design: Experimental repeated-measures study.
Objective: To investigate the effect of different extension forces applied to the palm of the hand on electromyographic (EMG) activity of the wrist extensor muscles during hand gripping.
Background: Lateral epicondylitis is usually caused by repetitive wrist extension that leads to an overuse injury. The current theory is that the process of lateral epicondylitis begins with an overuse injury that leads to microtearing of the extensor carpi radialis brevis muscle and occasionally the extensor digitorum communis muscle. Use of an external wrist extension force might reduce muscle activity during gripping.
Methods: Muscle activity was measured using surface EMG while subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction force without, and with, an applied external wrist extension force of 1%, 2%, and 3% of maximum voluntary contraction.
Results: Applying an extension force to the palm of the hand reduced EMG activity of the extensor muscles at the same strength generation during hand gripping. The muscles with the most significant reduction in EMG level, the extensor carpi radialis brevis and extensor digitorum communis, are those muscles that are most often involved with lateral epicondylitis.
Conclusions: This study shows that an external extension force reduces EMG activity of the wrist extensor muscles during gripping in healthy volunteers. As the extension force increased, a greater reduction in muscle activity was noted.

J Orthop Sports Phys Ther. 2004; 34(5):228-234.

Key Words: dynamometer, elbow, forearm, isometric force, lateral epicondylitis

Study Design: A randomized controlled prospective experimental study with some repeated measures.
Objectives: To characterize behavioral, sensory, motor, and nerve conduction decrements, and histological changes in the median nerve in rats trained to perform a high-force repetitive task.
Background: Understanding of work-related carpal tunnel syndrome is hampered by the lack of experimental studies of the causes and mechanisms of nerve compression induced by repetitive motion. Most animal models of nerve compression have not employed voluntary repetitive motion as the stimulus for pathophysiological changes.
Methods and Measures: Thirty Sprague-Dawley rats served as controls for 1 or more studies. Ten rats were trained to pull on a bar with 60% maximum force 4 times per minute, 2 h/d, 3 d/wk for 12 weeks. Motor behavior and limb withdrawal threshold force were characterized weekly. Grip strength and median nerve conduction velocity were measured after 12 weeks. Median nerves were examined immunohistochemically for ED1-positive macrophages, collagen, and connective tissue growth factor.
Results: Reach rate and duration of task performance declined over 12 weeks. Grip strength and nerve conduction velocity were significantly lower after 12 weeks than in controls. Limb withdrawal threshold increased between weeks 6 and 12. Median nerves at the level of the wrist showed increases in macrophages, collagen, and connective-tissue growth-factor-positive cells. These effects were seen in both the reach and nonreach limbs.
Conclusions: This animal model exhibits all the features of human carpal tunnel syndrome, including impaired sensation, motor weakness, and decreased median nerve conduction velocity. It establishes a causal relationship between performance of a repetitive task and development of carpal tunnel syndrome.

J Orthop Sports Phys Ther. 2004; 34(5):244-253.

Key Words: cumulative trauma disorder, median nerve, nerve compression, repetitive motion injury, work-related musculoskeletal disorder

Study Design: Mail survey of cheerleading-related training and injuries.
Objective: To collect and describe injury frequency, distribution, and associated factors related to the activity of cheerleading.
Background: Estimates indicate that more than 1 million participants are involved in cheerleading at various levels; however, little information exists relative to injuries and training. Unlike most other sports, cheerleader injuries are not tracked in a central database.
Methods and Measures: High school cheerleaders (mean age, 16.3 years) in 3 Midwest states completed questionnaires mailed to their respective high schools. Of the surveys mailed to 104 schools, 425 (32.2%) were returned and sufficiently completed for analysis.
Results: Participants reported an average of 4.1 years of experience and 61.9% of the respondents had sustained 1 or more career injuries. During the previous year, 41.3% had sustained 1 or more injuries (mean ± SD, 1.7 ± 1.9), resulting in an average of 3.4 reported missed practice or performance days. Of all injuries, the ankle (24.4%), back (16.1%), and wrist or hand (15.6%) were the most frequent sites of injury.
Conclusion: The rates of injury in cheerleading are comparable to rates of other sports. To accurately provide safety guidelines for all levels of cheerleading, a nationwide injury tracking system is necessary.

J Orthop Sports Phys Ther. 2004; 34(5):261-265.

Key Words: epidemiology, musculoskeletal injuries, sports, survey