Differential fore- and hindpaw force transmission in the walking rat.

Previous studies suggest that the stance phase of the rat stride is initiated by a soft contact period when the forepaw may engage in tactile sampling of the terrain. However, no ground reaction force measurements have yet been made during rat locomotion. In the dog and other quadrupeds a brief or nonexistent soft contact phase is observed. Therefore, forces and pressures exerted via fore and hindpaws have been measured in the spontaneously walking rat. These indicate while the hindpaw vertical reaction forces are temporally similar to those in the dog, those transmitted via the forepaw are not. At average walking velocities the forepaw soft contact time is some 4 times longer than that of the hindpaw, with values of 207 +/- 25 ms and 52 +/- 12.2 ms (mean +/- 1 SEM) respectively. These data are consistent with the idea of forepaw useage to provide tactile information of the terrain during a prolonged initial soft contact phase, while the hindpaw transmits most of the early vertical ground reaction forces.