Modification of the sit-to-stand task with the addition of gait initiation

This work was conducted to study the common task of initiating gait from a seated position. Ten subjects performed five trials each of sit-to-stand (STS) and sit-to-walk (STW). Centre of mass displacement and momentum, centre of pressure (COP) displacement and ground reaction forces were compared between conditions. Subjects significantly increased their linear momentum in both horizontal and vertical directions during and after seat unloading in STW compared to STS. Initiation of walking started around seat-off while subjects were still rising and COM projection was close to or behind the ankles. As balance is dependent on the initial momentum gained during the unloading phase, subjects who appeared to be more concerned with such balance broke their forward momentum and emphasized initial lateral displacement of the COP. Overall, the transitional task of STW is not a serial arrangement of two separate tasks, but a merging of a discrete task with a rhythmic one around the point of seat-off and the underlying strategies are heavily dependent on balance control.