Analysis of Rapid Stopping During Human Walking

Abstract

The mechanisms involved in rapidly terminating human gait were studied. Subjects were asked to walk at a comfortable speed and to stop walking as soon as they felt an electrical stimulus to the superficial peroneal nerve. This simulated hitting an obstacle with the top of the foot. Stimuli were presented repeatedly at random during a 20-min period of walking. Electromyograms and joint angular movements of the right leg and forces under both feet were recorded. The step cycle was divided into 16 parts, and the responses to stimuli in each part were analyzed separately. Subjects generally stopped with the right foot in front of the left or vice-versa, depending on when the stimulus was applied in the step cycle. There was also a transition region in which subjects would rise up on their toes and either back down or take one more quick, short forward step. Three different mechanisms were used to produce a stop. 1) An extension synergy in the swing leg was initiated just before this leg hit the ground to brake the forward momentum of the body. 2) The push-off phase of the stance leg was inhibited to reduce the forward thrust and maintain the stance leg on the ground behind the body. 3) If these mechanisms were insufficient, the body rose up onto the toes of the extended forward leg and thereby converted more kinetic energy to potential energy. A decision to take an additional step depends on whether the momentum of the body is sufficient to carry the center of mass in front of its support on the forward leg. If so, an additional step is taken. Despite the complexity of the decisions that must be made, changes in electromyographic activity are seen throughout the legs and trunk in 150-200 ms.

Gait termination in lower limb amputees

“…Another limitation was that only outcome variables in the last step were assessed. Although most deceleration occurs in this step [7,22,23], other studies have shown important adjustments in the trailing limb in the step prior to termination, namely a decrease in push-off GRF [5,8,9,11]. Finally, due to technical limitations the data of leading limb preference, temporal variables and joint angles were collected in different runs than the GRF and COP data.…”

“…For safe gait termination, forward movement of the body has to be slowed down to achieve a stable upright position [2,5]. In able-bodied persons the leading limb, which is the limb that stands still first, is mainly responsible for the production of the necessary braking ground reaction force (GRF).…”

“…Compared to normal walking the braking GRF is increased in the final stance phase [6][7][8]. A large burst of soleus muscle activity and reduced activation in the tibialis anterior muscle of the leading limb bring the foot flat to the ground [5,7,9,10]. The vasti and gluteus medius muscles are activated, respectively, to extend the knee and to prevent the trunk from bending forward.…”

“…In the trailing limb the tibialis anterior, biceps femoris and gluteus medius muscles increase activity to bring the body down and backwards with the foot flat to the ground, resulting in a further decrease www.elsevier.com/locate/gaitpost Gait & Posture 27 (2008) [82][83][84][85][86][87][88][89][90] in forward movement [9]. The muscle activity moves the centre of pressure (COP) anteriorly and keeps the centre of mass (COM) behind the leading limb [5,9]. The position of the COP in front of the COM and the increased braking GRF lead to deceleration of the body [11].…”

Modulation of reflex responses in activated ankle dorsiflexors differs in healthy young and elderly subjects

“…Surprisingly, very little is known about the adaptation of the dorsiflexor muscles during ageing (Obata et al 2010). However, these muscles play an important role in locomotion (Ceccato et al 2009;Hase and Stein 1998;Zehr and Stein 1999) by lifting the foot during the swing phase and preventing tripping. They are also involved in postural responses to stance perturbations (Nardone et al 1995;Stelmach et al 1989) and unexpected slips during walking Woollacott 1998, 1999).…”