The purpose of this study consists in evaluating the efficiency of the preload device on safety belt during an impact. This device is designed to improve the three-point belt restraint by ensuring a better coupling between the car and the occupant at the impact beginning.

To solve the problems due to the compressive loads on the thorax, a living model has been chosen:​ the baboon which offers interesting similarities with man. Impact tests are conducted on a dynamic sled at 8.3 and 13 m/s speeds. In order to reduce the variables, the baboon is sat on a rigid seat on which it is restrained by a four point harness preventing lateral movements, the preload being applied on the shoulder straps.

The first experimental stage consists in applying the preload level just before the crash in order to define realistic levels. The test analysis includes the study of the animal kinematics and that of the shock parameters, head and thorax deceleration and strap loads. This analysis indicates that the preload level has a great influence on the measured parameters. In fact, when the preload increases, the head decelerations decrease with the body displacements. Moreover, the use of a living animal has been very helpful in the assessment of possible risks for the body such as thoracic fractures or respiratory disturbances.

The second stage will consist in evaluating the efficiency of the preload given by pyrotechnical jacks adjusted for three load levels.