Patients received one session of EPI technique per week over 4 weeks (or over 6 weeks when pain persisted) associated with a home program consisting of eccentric exercise (EccEx) and stretching, initiated 24 hours after each session. The EccEx and stretching program was taught by a physiotherapist in the first session and monitored in subsequent sessions. At discharge, patients were instructed to perform only EccEx once daily for the first 6 weeks of the follow-up period.

The EPI technique was performed under ultrasound-guidance on the clinically relevant area (or areas of maximum tenderness to palpation and with ultrasonographic degenerative tendon changes) using an intensity of 4-6 milliampere (mA) during 3 seconds, approximately 3 times. The investigators used the EPI machine (Cesmar Electromedicina S.L., Barcelona, Spain) and a GE Logiq E Portable Ultrasound Machine with GE Linear probe 12L-RS (5-13 mhz) (GE Healthcare, Wisconsin, EEUU). During the EPI technique, the patient was placed in a supine position, with the affected elbow placed in a position of 90° flexion and maximum pronation. The elbow was sterilized and the sonographic transducer, enclosed in a sterile cover over sterile applied gel, was placed at the lateral epicondyle (first approach) and over the humeroradial joint between the head of the radius and the capitulum of the humerus (second approach), where it remained throughout the procedure. A common target area was the deep surface of the common extensor tendon (origin of the ECRB \[extensor carpi radialis brevis\] and the EDC \[extensor digitorum communis\]) (first approach) and the deep surface of the ECRB, over the capsule and the lateral ulnar collateral ligament (second approach). A 0.3 x 25mm. (1 inch) needle was inserted at a 30° to 45° angle to the skin in the direction of the lateral epicondyle (first approach) and at a 80° angle to the skin, with the needle tip directed towards the humeroradial joint (second approach). In the first approach the needle was advanced parallel to the longitudinal plane of the tendon (in-plane approach); whereas in the second approach the needle was advanced along the short plane of the humeroradial joint (out-of-plane approach). Real-time ultrasonographic imaging provided guidance for both procedures. Once the needle reached the target tissue, readjustments of the needle position were made in order to ensure a correct stimulation. The generation of the galvanic current creates a white image (hyperechoic) as a result of the liberation of hydrogen gas due to the electrolysis. Oral paracetamol was used when necessary for the purpose of pain relief only.

The eccentric exercise program consisted of three series of up to 10 repetitions of eccentric work, repeated twice daily (morning and afternoon), under maximum load (initially with one kilogram) in an optimal and functional pain-free range. From maximum wrist extension and radial deviation, rapid wrist flexion movement were performed, followed by a 2-second hold of the final position. In between series patients were given a rest period of 2-3 minutes. This formula was used for the duration of the physiotherapy program. The concentric contraction phase for returning to the starting position was nullified with the help of the other hand.

The stretching program consisted of a stretching exercise for the epicondylar muscles consisting in three series of 7 repetitions twice a day (morning and afternoon), performed in a sitting position with a flexed wrist and fingers, ulnar deviation and elbow extension reaching the stretch limit without bounces, and held for 45 seconds, with a 30-second rest between repetitions.