Abstract：Muscle damage is easily occurred after eccentric exercise. Therefore, muscle warm-up is routinely recommended as an alternative way to prevent the muscle damage or injury. Ultrasound (USD) is an ideal way to elevate muscle temperature, but the protective effect of ultrasound exposure on eccentric exercise-induced muscle damage is remains unclear. The purpose of this study was to examine whether preconditioning with ultrasound diathermy prior to eccentric exercise could attenuate the muscle damage. Eight healthy male university students were voluntarily participated in this study. Each subject performed two protocols in a randomized order (no treatment and ultrasound preconditioning) prior to maximal eccentric contraction for the non-dominant hand. Creatine kinase (CK) activity, maximal voluntary isometric contraction strength (MVIC), range of motion (ROM) and muscle stiffness (acoustic radiation force impulse, ARFI) were measured before treatment (baseline), and immediately, 2nd, 4th, 7th and 10th day after eccentric exercise. The results showed that USD treatment prior to eccentric exercise appears to be beneficial than without treatment in attenuating the symptoms of eccentric exercise-induced muscle damage. This was indicated by higher MVIC, lower muscle stiffness, lower CK activity and a significant faster recovery from ROM. Although all symptoms of eccentric muscle damage have been changed significantly following eccentric exercise, the USD treatment may increase the temperature of muscle and connective tissue, which would reduce muscle viscoelastic and increase muscle extensibility. Therefore, USD has a prophylactic effect on reducing the elbow flexors muscle damage in young colleg e students. (Full text)