The purpose of this study is to examine the activity of elite swimmers confronted with an underwater technical device (MAD system) used to estimate the biomechanical factors of performance. It consists in using biomechanical and experience data for a better understanding of activity in sport and, more broadly, to better understand activity. The data were produced from two different approaches to analyzing activity. The first approach is an activity-centered approach: the “course of action” empirical research program. The second is the biomechanical approach which analyzes activity by focusing on the mechanical properties of movements. These two approaches were integrated (a) for a better understanding of the swimmers’ interactions with the device and the modalities of construction of their swimming activity, and (b) to draw from conclusions for designing this device to optimize its evaluation function. Three international swimmers participated in the study. Three types of data were collected: video recordings of the swimmer’s behaviors, biomechanical data measuring the speed and propelling strengths of the swimmer, and verbalization data from interviews about the swimmer’s experience. The data were processed in three steps: analyzing (a) the biomechanical data and (b) each swimmer’s experience, and (c) reconstructing and comparing each swimmer’s course of information by the integration of the biomechanical and course of experience analysis. The results showed a variation of the activity for all swimmers in the context of evaluation: three forms of activities conditioned the dynamics of their interactions with the device. They revealed that the swimmer’s activity is determined by the physical characteristics of the device and the swimming speed conditions prescribed by the protocol of evaluation. Only the threshold of the “fast speeds” guarantees an optimal appropriation of the device by the swimmers. Using these biomechanical and experience data, this study highlights and discusses the problem of technical device appropriation during a sport evaluation protocol. It also underlines the mutual contributions of the biomechanical and experience data (a) to understand the swimmers’ activity during an evaluation and (b) to design proposals for using the MAD system in evaluation and training sessions.