The incorporation of external tools during a sports activity can be analyzed through the dynamics of appropriation. In this study, we assumed that appropriation could be documented at both the phenomenological and behavioral scales and aimed to characterize trail runners' interactions with five carrying systems (i.e., backpacks proposing different ways of carrying water) in an ecological setting. The runners ran a 3-km trail running loop, equipped with inertial sensors to quantify both their vertical oscillations and those of the carrying systems. After the trials, phenomenological data were collected in enactive interviews. Results showed that (1) the runners encountered issues related to the carrying system, whose emergence in their experiences while running revealed the interplay between the tool's transparency (i.e., when runners provided no account of the carrying system) and opacity (i.e., when runners mentioned perceptions of disturbing system elements), and (2) when the runners carried the water bottles on the pectoral straps, they felt the system bouncing in an uncomfortable way, especially in the less technical parts of the route. We therefore investigated the low- and high-order parameters of coordination by computing the vertical accelerations and the acceleration couplings between the carrying system and the runners in order to identify coordination modes. The congruence between the runners' experiences and the behavioral data was noted in terms of (1) the system's vertical oscillations (i.e., low-order parameters) and (2) the couplings between the accelerations of the runners and the backpacks (i.e., high-order parameters). Our results demonstrated that the appropriation process was shaped by the interactions between the runners' activity, the environment and the physical properties of the tool. These interactions occurred in fluctuating phases where the runners perceived the carrying systems as more or less incorporated. Our results highlighted how tool incorporation is revealed through changes in its transparency/opacity in the actor's activity.