[Differences in anticipatory postural adjustments between self-generated and triggered gait initiation in 20 healthy...

Preparation of upper-limb movements differs between self-paced and triggered conditions. This study analyzed the anticipatory postural adjustments (APAs) of gait initiation in normal subjects in 2 conditions: self-generated and triggered by a "beep" sound.

We recorded kinematic, spatiotemporal parameters of the first two steps by means of video motion analysis (6 infrared cameras), and kinetic parameters (using a force platform and the optoelectronic system) in 20 normal subjects. Two conditions: 1) self-generated initiation; and 2) initiation triggered by a "beep" sound were studied to evaluate the APA phase, by recording kinetic data (duration of the APAs, trajectory of the center of pressure, speed and trajectory of the center of mass). Kinematic data (first and second step speed, length and duration) were also recorded.

First step speed and length were increased in self-paced gait initiation compared to triggered gait initiation in controls. We found no difference between the 2 conditions in terms of second step kinematic data. It was caused by a significant difference between the 2 conditions for the temporal characteristics of anticipatory postural adjustments (APAs) in the initiation of the first step, which was longer when normal subjects performed self-generated gait initiation. The trajectory of center of pressure and center of mass remained the same in the 2 conditions.

APAs of gait initiation process are delayed under self-paced condition, although they do not differ qualitatively between reaction time and self-paced condition. Neuphysiological support of self-generated movement could explain these differences.