Functional activation of the extensor carpi radialis muscles in humans.

OBJECTIVES: To assess activity of radial wrist extensors caused by isometric radial deviation and extension by using magnetic resonance imaging (MRI) and to assess measures that might be used to normalize T2-weighted data. DESIGN: Two-way analysis of variance (ANOVA) design. SETTING: Laboratory and children's hospital. PARTICIPANTS: Three healthy volunteers. INTERVENTIONS: Ten repetitions of 10-second randomly ordered 30% or 60% of maximum voluntary isometric contractions toward wrist extension or radial deviation. MAIN OUTCOME MEASURES: Average T2 values from T2-weighted MR images of the extensor carpi radialis brevis (ECRB) and the extensor carpi radialis longus (ECRL), flexor digitorum profundus (FDP), and radius marrow were determined across 7 sections and 4 exercise bouts and a preexercise condition. RESULTS: Significant differences across task and across sections were determined. Post hoc analysis revealed differences in activity between proximal and distal ECRB and ECRL during an exercise and differential activation of the same muscle across the 2 exercise tasks. Bone marrow and FDP did not show task-related changes. The range of average T2 values of bone marrow across sections was greater than a muscle (FDP) that was not the target of the exercise protocol. However, FDP did show small but significant differences across sections. CONCLUSIONS: T2-weighted MR images can be used to study muscle activation at 30% and 60% of maximum voluntary contractions. The use of inactive muscle and bone marrow for normalizing data requires further investigation.

Shoulder range of motion in elite tennis players. Effect of age and years of tournament play.

We studied glenohumeral rotational range of motion in 39 members of the United States Tennis Association National Tennis Team and touring professional program. We took goniometric measurements of internal and external rotation of dominant and nondominant shoulders at the glenohumeral joint with the humerus at 90 degrees of abduction. We categorized the tennis players by age and by years of tournament play. Results were analyzed by total rotation, internal rotation, external rotation, and dominant-to-nondominant shoulder differences. In our results, dominant internal rotation of the shoulder declined and the difference between dominant and nondominant internal rotation increased with both age and years of tournament play. Men and women tennis players showed the same degree of deficits in range of motion. Significant analysis of variance statistics were calculated for dominant internal rotation with years of total play, dominant total rotation with years of total play, and nondominant total rotation with age. Moderate negative correlations were found between dominant internal rotation and years of total play and dominant total rotation and years of total play. These results indicate a loss of internal rotation that seems progressive with longer periods of play. This loss of internal rotation of the shoulder is an absolute loss of motion because total rotation also decreases. Early detection and a corrective training program should be considered because adaptations may result in deleterious biomechanics affecting both performance and risk of injury.