Work related upper extremity disorders are associated with cumulative trauma resulting from the continuous use of forearm muscles rather than from a specific incident. The aim of this work is to compare wrist extensor muscles activation between patients with lateral epicondylitis and healthy subjects. Differences can be used in the design of rehabilitation or injury prevention programs according to biomechanical deficits. Surface EMG signals from three forearm extensor muscles (Carpi Radialis-ECR, Digitorum Communis-EDC and Carpi Ulnaris-ECU) were recorded by linear electrode arrays in wrist extension as well as during selective contractions. Average Rectified Values (ARV) were calculated in order to identify the contribution of each muscle to different tasks. On the other hand, Muscle Fiber Conduction Velocity, Mean and Median Frequencies and also ARV were studied to obtain fatigue indexes related to metabolic changes in the muscles during a high force sustained contraction. Results showed muscular imbalance with lower ECR activity compensated by higher ECU activation, and higher fatigue indexes in patients with lateral epicondylitis.