Comparison of trunk activity during gait initiation and walking in humans

Abstract

To understand the role of trunk muscles in maintenance of dynamic postural equilibrium we investigate trunk movements during gait initiation and walking, performing trunk kinematics analysis, Erector spinae muscle (ES) recordings and dynamic analysis. ES muscle expressed a metachronal descending pattern of activity during walking and gait initiation. In the frontal and horizontal planes, lateroflexion and rotation occur before in the upper trunk and after in the lower trunk. Comparison of ES muscle EMGs and trunk kinematics showed that trunk muscle activity precedes corresponding kinematics activity, indicating that the ES drive trunk movement during locomotion and thereby allowing a better pelvis mobilization. EMG data showed that ES activity anticipates propulsive phases in walking with a repetitive pattern, suggesting a programmed control by a central pattern generator. Our findings also suggest that the programs for gait initiation and walking overlap with the latter beginning before the first has ended.

Figure 1. Gait initiation and walking cycle parameters: definition.

A) Trajectory of left and right ankle displacement in the forward direction for gait initiation and walking. The beginning and end of the cycle are set when the two curves cross each other in the same direction. B) Inter-ankle distance in the forward direction for gait initiation and walking. The beginning and end of the cycle are set when the curve crosses the 0 in the same direction.

Figure 2. Definition of main events from inter-ankle distance and force plate during gait initiation and walking.

A) Mean±SD inter-ankle distance on the three axes of space during gait initiation and walking in one subject. B) Mean±SD of vertical resultant force along Y axes on each force plate (R, Right, L, Left) allowing definition of events and phases of gait initiation and walking cycle.

Figure 3. Leg muscle EMGs and center of pressure (COP) trajectory.

A) Right tibialis anterior (rTA) anf left gasctrocnemius (lGN) electromyographic activity during gait initiation and walking for one trial and one subject. B) COP trajectory reconstruction obtained from the force plate signal during one trial of gait initiation and one trial of walking.

Figure 4. Erector Spinae (ES) muscle activity during gait initiation and gait.

A) Rectified and smoothed (moving average) traces of all bilaterally recorded ES muscle from C7 to L3, for one trial and one subject during gait initiation and walking. B) Bar diagram presenting the phase of activity of ES muscle during gait initiation and walking. Each bar indicates the time during which each muscle was active. Black bars represent main activity and grey bars represent secondary activity. Small triangles represent the localization of corresponding peaks for each activity.

Figure 5. Stick diagrams of spine kinematics in the three planes: sagittal, frontal and horizontal.

Each dot represents the position of one recorded vertebral level (C7, T3, T7, T12, L3, S1). Sticks are drawn for each 10% of gait initiation and walking. Bottom bar indicate phases of gait initiation and walking cycle. A) Sagittal plane. B) Frontal plane. Gray areas indicate main activity of ES muscle at each level. C) Horizontal plane.

Figure 6. Sagittal plane kinematics during gait initiation and walking.

A) Angle definition at thoracic level (Thor), T7, T12, L3 and pelvis (Pel). B) Curves present the mean±SD of angle changes for all subjects for gait initiation and walking. Triangles indicate the mean±SD of the positions and amplitudes of maxima and minima for all subjects.

Figure 7. Frontal plane kinematics during gait initiation and walking.

A) Angle definition at shoulder level, T7, T12, L3 and superior iliac spines (SIS). B) Curves present the mean±SD of angle changes for all subjects for gait initiation and walking. Triangles indicate the mean±SD of the positions and amplitudes of maxima and minima for all subjects.

Figure 8. Horizontal plane kinematics during gait initiation and walking.

A) Angle definition at shoulder level, thoracic level (Thor), L3 and superior iliac spines (SIS). B) Curves present the mean±SD of angle changes for all subjects for gait initiation and walking. Triangles indicate the mean±SD of the positions and amplitudes of maxima and minima for all subjects.

Figure 9. EMGs versus kinematics.

Plain curve represents the difference between right and left normalized EMG at C7, T3, T7, T12, L3 and S1 levels. Filled circle indicates the mean±SD of curve zero crossing instants for all subjects, i.e. the time at which the side of strongest ES muscle activity changes. Dotted curves represent frontal angles of the spine at T7 and L3 level. The triangles indicate the corresponding maxima (as in figure 7) and represent the inversions of curvature directions. A, during gait initiation and B, walking.

Figure 10. Cartoon of trunk activity.

Each picture is a schematic representation of trunk movements and activities at a given time during gait initiation phase and walking cycle.