Constant Wrist Extension Force Decreases Extensor Carpi Radialis Activity With Gripping

Abstract

The extensor capri radialis (ECR) muscle is commonly associated with tennis elbow (TE). When an individual grips an object such as a tennis racket, the ECR muscle functions to counter the finger flexors' duel functions as an isometric finger flexor/wrist flexor. Previous research indicates the ECR is a compensating wrist extension counter-moment during gripping. Exploring ways to lessen the muscles activity of the ECR during gripping tasks, such as playing tennis, could be beneficial. PURPOSE: To determine the influence of a wrist extension moment on ECR activity when gripping a tennis racket handle. METHODS: Twenty injury free participants, (10 male, 10 female), volunteered for this study (Age = 23.67 + 2.36 years). The skin was properly prepped then surface electromyography (EMG) electrodes were placed over the ECR of the dominant arm. A reference maximal volitional isometric contraction (MVIC) of the ECR during gripping of a tennis racket handle (racket head removed) was performed. ECR activity of Grip condition (G) was obtained by participants gripping an intact tennis racket with the instruction of using normal tennis racket grip force. The reference grip force, obtained in condition G, was measured using finger force transducers. Grip Wrist Moment condition (GWM) was obtained by instructing participants to replicate the grip force of condition G (within 5%) on a tennis racket handle with an added wrist extension moment to the wrist (Grip Wrist Moment). A dependant samples t-test was utilized to compare %MVIC of conditions G and GWM. RESULTS: A significant decrease was noted in % MVIC of the ECR from G to GCM conditions (G = 20.8 MVIC + 12%, GWM = 13.9 MVIC + 14.7%)(p < 0.05). CONCLUSIONS: The results suggest that applying an external wrist extension influence could lessen the activity of the ECR muscle during functional gripping, which has many implications for tennis players trying to rehabilitate from lateral epycondylitis (tennis elbow). The design of sporting equipment, containing a constant wrist extension force to lessen ECR activity while playing, would be beneficial to many athletes.