The time reversal process is a well-known method of obtaining focused waves. When used at Lamb guided acoustic waves it permits compensating the dispersion of each propagation mode providing a time recompressed focused signal. The time reversal operator in a closed medium is very dependent on the geometry and physical characteristics of the medium. The good focusing capability of the process can be used to detect changes in medium boundary conditions. The mismatch of the impulse response transfer function of the medium, especially in the phase of its frequency components, causes loss in the focusing quality, and so degrades the received signal shape. In this work it is proposed the use of the time reversal technique to detect the variation on the external applied traction in a plate structure. Experiments were performed in transmission-reception mode for two fixed ultrasonic transducers spaced in an aluminum plate where Lamb waves have been excited by a wideband pulse. A variable longitudinal traction is applied to the plate and the received time reversal signal is observed. As the received signal with no traction difference has a well-defined shape, the analysis of the process traction sensitivity is simplified. Digital filtering in the frequency domain was used at the transmitted time reversed signal in order to receive a broader spectrum signal, enhancing the process focus quality and stress sensitivity. The external traction sensitivity was verified. The observed phase spectrum variation indicated a wave path change, caused by the deformation of the plate. The peak value has been decreased for the applied traction and returned to it maximum value as the traction difference was removed. Also, the group delay has changed during the traction process. A model for the peak position has been proposed and compared with the measured experiments. The results show that the high sensibility of the time reversal signal technique due to changes of the geometry of the closed medium can be used as strain variation pointer.