Design and analysis of a constant-force bench press

Abstract

In strength or resistance training, the patterns of movement of the load and the muscle activation can be adapted to the training objective according to the muscle conditioning machine selected. Traditionally, free-weight bench press is extensively used for athlete training. One of the main features of such kind of machine is the significant influence of the inertial forces in the muscle forces that the athlete has to develop. In this paper, a bench press which is able to maintain an almost constant force resistance is proposed. Then, the proposed constant-force bench press is compared to the traditional free-weight resistance bench press. Experimental data measured in a test session with free-weight resistance are used as an input for a mathematical model of the bench press that allows estimating three meaningful variables of the exercise performance: the shoulder vertical force, the net joint moment at the shoulder and the muscular power. These results are compared with those obtained by assuming a constant-force resistance, finding significant differences between both resistance systems. Constant-force resistance results in a less fluctuating force curve, lower peaks of the joint moment and muscular power, and small variance between different exercise repetitions.