Evidence for a common process in gait initiation and stepping on to a new level to reach gait velocity

Abstract

The aim of this study was to examine the adaptability of the gait initiation process when confronted with stepping on (SO) to a new level. Eight young adults performed gait initiation at two different speed conditions in a level walking (LW) situation and in a SO situation aimed at walking on an elevated (16 cm) level surface. As in a previous study using a single step, we found in SO a contradiction between the characteristics of anticipatory postural adjustments (APA) and gait velocity, i.e. the peak of anteroposterior velocity of the body's centre of gravity (CG) reached at the end of the first step. In normal and fast gaits, gait velocity was similar in both situations, whereas the duration and amplitude of the APA were smaller in SO than in LW. The reduction of APA in SO allowed the forward velocity of CG at the time of foot contact of the stepping limb to be lower than in LW. This is explained by the fact that the majority of body lift, beginning at this time, required a greater increase in forward velocity than in LW. Thus, with lower APA in SO, the gait velocity could be similar in both situations. From LW to SO, the spatio-temporal patterns in the forward velocity of CG varied within characteristic phases of the movement, but in a predictable way as gait velocity changed. These results gave evidence of an adaptation of the gait initiation process for the new constraints, despite the contradiction between APA and gait velocity. The spatio-temporal parameters of the anticipation phase in SO were pre-set according to the new requirements of the task: reaching gait velocity with a body lift. Furthermore, the time for reaching gait velocity was independent of both the amplitude of this velocity and the situation. This expressed the capacity of the subjects to use in SO the same optimal conditions to reach gait velocity as in LW, i.e. essentially in a ballistic manner.

Combined effects of speed and directional change on postural adjustments during gait initiation

“…In steady-state gait, this thrust is known to accelerate the body forwards and upwards into the next swing phase (Patla et al, 1991) as laterally exhibited during constant velocity circular walking (Orendurff et al, 2006), straight walking (Patla et al, 1991) and during turning steps (Glaister et al, 2007b;Patla et al, 1999). Evidence of this thrust is also shown when gait is initiated onto a higher level (Gelat et al, 2006).The lifting of the body that occurs after heel strike of the swing limb causes an additional forward acceleration of the CM and by the end of the first step, the CM velocity is the same regardless of whether gait is initiated onto a higher level or at the same height (Gelat et al, 2006). This thrust also possesses a medial-lateral component as the size of the lateral component of this thrust could be varied by adjusting the exact direction and size of the external force exerted by the rear leg.…”

Anticipatory Postural Adjustments During Lateral Step Motion in Patients With Hip Osteoarthritis

“…The peak mediolateral ground reaction force which was defined as the force that moves the CoM to the supporting side (Fx-support) and to the stepping side (Fx-step) during the anticipation phase was measured. In step initiation, the anticipation phase has been defined as the period from the onset of the center of pressure (CoP) shift to the foot-off of the stepping leg (Gélat et al, 2006;Liu et al, 2003). The Fx-support and Fx-step were standardized by the body weight of each subject.…”

Relationship between gait initiation and disability in individuals affected by multiple sclerosis

“…The backward shift of the COP during the APAs serves to propel the center of mass (COM) forwards and to reach the intended gait velocity at the end of the first step (Brenière et al, 1987;Brunt et al, 1999;Couillandre et al, 2000;Gélat et al, 2006;Lepers and Brenière, 1995). Thus, the reduction point B represent a strategy to decrease the forward propulsion of the COM and LOC speed in order to make safer the gait initiation.…”

“…Stability is further affected because the wide base provided by bipedal support is replaced by a more narrow and unstable unipedal position (Martin et al, 2002(Martin et al, , 2006. The GI gives a fundamental contribution to the forward progression (Brenière et al, 1987;Brunt et al, 1999;Couillandre et al, 2000;Gélat et al, 2006;Lepers and Brenière, 1995) and to the postural stability (Caderby et al, 2014;McIlroy and Maki, 1999). Thus, GI represents a natural but deliberately destabilizing task and can be a valid instrument in assessing the balance ability of subjects with neurological and motor impairments as in the case of MS.…”