Wrist Extension Counter-moment Force Effects on Muscle Activity of the ECR With Gripping: Implications for Lateral Epicondylagia
Type of DegreeDissertation
Health and Human Performance
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Studies have suggested that the muscle most commonly associated with lateral epicondylalgia (tennis elbow) is the extensor carpi radialis (ECR). Gripping elicits pain in persons symptomatic with this condition. The common factor between recreational, occupational, and daily living activities that lead to lateral epicondylagia is gripping. The isometric grip creates a wrist flexion moment due to the finger flexor tendons crossing the wrist joint. Our wrist extensor muscles must counter this wrist flexion moment created by our finger flexors if the wrist is to remain in a neutral posture. Gripping then naturally innervates the wrist extensor muscles, which attach on the lateral epicondyle. The lateral epicondyle is the point of irritation for persons symptomatic with lateral epicondylagia. If the wrist was afforded an external wrist extension counter-moment force, would the internal wrist extensors be less active? Less activity would be beneficial as it would lead to less cumulative stress being placed on the lateral epicondyle where the ECR originates. The purpose of this research is to determine if the presence of an external counter-moment force will decrease the activity of the ECR during various gripping activities in asymptomatic and symptomatic persons. As the ECR is the primary muscle associated with TE, any significant decrease noted in the EMG activity of the ECR could lead to promising advances in the etiology of TE. Understanding the effects of an external counter-moment force on the muscle activity associated with TE, would lead to advances in rehabilitation, symptom relief braces, and eventually lead to a better understanding of how this pathology originates and persists. Forty-eight subjects, 10 male and 10 female for each asymptomatic section, and 4 male and 4 femail for the symptomatic section volunteered as participants in this study. Participants in the max counter-moment force section maximally gripped while also pushing against a static counter-moment force device at various levels of maximal wrist extension counter-moment force intensity (0%, 25%, 50%, 75%, 100%). Participants in the task counter-moment force section gripped three items (hammer, tennis racket, and gallon of tea). The grip force was measured and then matched in the subsequent trial where an external wrist extension counter-moment force was applied. Participants in the symptomatic section maximally gripped a handle then rated their perceived discomfort. After a rest, they again maximally gripped a handle which had a wrist extension counter-moment force then rated their perceived discomfort. Counter-moment forces were measured using the AMTIä OR6-7-1000 Biomechanics Sport Platformâ. Muscle activity was measured using the Noraxonâ Myosystem 1200ä electromyography system. The counter-moment force which was supplied during the task and symptomatic counter-moment force sections was supplied by the Marcyâ Wedgeä. Grip magnitude was measured using the Economical Load & Force System (ELFâ) by Flexiforceä. Repeated measures ANOVA’s were used for each research section. Results indicate in the maximum counter-moment force study that any counter-moment force intensity (25%, 50%, 75%, 100%) while maximally gripping significantly lowers muscle activity of the ECR muscle compared to maximal gripping alone. There is no significant difference however between counter-moment force trials (25%, 50%, 75%, 100%). Results also indicate that the presence of a wrist extension counter-moment force decreases muscle activity of the ECR muscle when gripping a hammer, tennis racket, and gallon of tea. These findings provide the basis for future investigations into the role of wrist extension counter-moment forces and how the application of these may alleviate symptoms of lateral epicondylagia.