[en] The purpose of this study was to investigate the reproducibility of findings derived from a new iso-inertial dynamometer during bench press (BP) and squat (SQ) and to provide descriptive data for recreational athletes. A position transducer and accelerometer were combined to assess velocity and power during free weight lifting exercises. Simulated movement with a pulley system revealed the excellent technical consistency of the dynamometer. Sixteen male subjects participated in the study. Iso-inertial tests consisted of lifting as fast as possible four different relative loads (35, 50, 70, 90% 1RM in BP and 45, 60, 75, 90% 1RM in SQ). The test was repeated one week later. Analysis of variance revealed no significant variation between sessions or trials. Reproducibility was better in velocity than in power, although it remained fairly good in both exercises (coefficients of variation [CV] never exceeding 10%) except for the time to peak power parameter. Descriptive data confirmed the classical force-velocity and force-power relationships for BP and SQ. In conclusion, this study demonstrated reliable measurements in BP and SQ iso-inertial exercises. Monitoring force-velocity and force-power relationships offers an original functional approach in strength training supervision.