The aim of this investigation was to analyze the effects of an eccentric strength training protocol using supramaximal loads (>1 repetition maximum [1RM]) on different maximal and explosive strength parameters of the lower extremity. The eccentric maximal strength (EX max), maximal isometric strength ("maximal voluntary contraction" [MVC]), 1RM, explosive strength ("rate of force development" [RFD]), countermovement jump, and squat jump height were tested before and after a training period of 6 weeks. The training group was composed of 15 individuals with low-weight training experience and a control group of 13 subjects, also with a low-weight training experience. The lower extremities were trained 3 days per week using a 45° leg press. Each training session comprised 5 sets of 3 repetitions with a 6-minute rest between each set. The training weights were adjusted continuously during each training session and between training sessions. In each case, a load was chosen that could be lowered unilaterally in a controlled manner by the subjects. For the concentric part of the exercise, 2 investigators lifted the weight to the starting position. After 6 weeks, strength training with supramaximal loads showed a significant increase in EX max (28.2%, p < 0.001) and 1RM (31.1%, p < 0.001). The increases observed in the control group were not significant. Changes in MVC, RFD, and vertical jump heights were not significant in both groups. The results of this study suggest that in untrained subjects, unilateral eccentric strength training in the leg press generates equal and significant improvements in unilateral eccentric and bilateral eccentric-concentric maximal strength, with a nonsignificant transfer to vertical jump performances and unilateral isometric force production.