To compare the kinematics and electromyography of the periscapular muscles in swimmers before and after a 3-min maximal effort test.16 competitive swimmers.Infrared cameras were used to record kinematics in the scapular plane in synchronization with the electromyography system.There was an increase in internal rotation in all angles (p < 0.05), an increase of the anterior tilt, with 120° of elevation (p = 0.04). The serratus anterior showed a decrease in the intervals of 120-90° and 60-30° (p = 0.04; p = 0.02). There was a linear relationship between the variation before and after the maximal effort of the anterior tilt in relation to the variation of muscular activation of the transverse trapezius (p = 0.01) and the lower trapezius (42%, p = 0.01); an internal rotation in 120° and 90° of elevation in relation to the transverse trapezius (p = 0.01); and an internal rotation in 60° and 30° of elevation in relation to the serratus anterior (p = 0.04, p = 0.03).A maximal 3-min effort test resulted in altered scapular biomechanics. More studies are needed to verify if the changes correspond to a risk factor for injuries.