Mathieu de Sèze

Coordinated network functioning in the spinal cord: An evolutionary perspective

The successful achievement of harmonious locomotor movement results from the integrated operation of all body segments. Here, we will review current knowledge on the functional organization of spinal networks involved in mammalian locomotion. Attention will not simply be restricted to hindlimb muscle control, but by also considering the necessarily coordinated activation of trunk and forelimb muscles, we will try to demonstrate that while there has been a progressive increase in locomotor system complexity during evolution, many basic organizational features have been preserved across the spectrum from lower vertebrates through to humans. Concerning the organization of axial neuronal networks that control trunk muscles, it has been found across the vertebrate range that during locomotor movement a motor wave travels longitudinally in the spinal cord via the coupling of rhythmic segmental networks. For hindlimb activation it has been found in all species studied that the rostral lumbar segments contain the key elements for pattern generation. We also showed that rhythmic arm movements are under the control of cervical forelimb generators in quadrupeds as well as in human. Finally, it is highlighted that the coordination of quadrupedal movements during locomotion derives principally from an asymmetrical coordinating influence occurring in the caudo-rostral direction from the lumbar hindlimb networks.

Comparison of trunk activity during gait initiation and walking in humans.

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.

Sequential activation of axial muscles during different forms of rhythmic behavior in man

In humans, studies of back muscle activity have mainly addressed the functioning of lumbar muscles during postural adjustments or rhythmic activity, including locomotor tasks. The present study investigated how back muscles are activated along the spine during rhythmical activities in order to gain insights into spinal neuronal organization. Electromyographic recordings of back muscles were performed at various trunk levels, and changes occurring in burst amplitudes and phase relationships were analyzed. Subjects performed several rhythmic behaviors: forward walking (FW), backward walking (BW), amble walking (where the subjects moved their arms in phase with the ipsilateral leg), walking on hands and knees (HK) and walking on hands with the knees on the edge of a treadmill (Hand). In a final task, the subjects were standing and were asked to swing (Swing) only their arms as if they were walking. It was found that axial trunk muscles are sequentially activated by a motor command running along the spinal cord (which we term “motor waves”) during various types of locomotion or other rhythmic motor tasks. The bursting pattern recorded under these conditions can be classified into three categories: (1) double-burst rhythmic activity in a descending (i.e., with a rostro-caudal propagation) motor wave during FW, BW and HK conditions; (2) double-burst rhythmic activity with a stationary motor wave (i.e., occurring in a single phase along the trunk) during the ‘amble’ walk condition; (3) monophasic rhythmic activity with an ascending (i.e., with a caudo-rostral propagation) motor wave during the Swing and Hands conditions. Our results suggest that the networks responsible for the axial propagation of motor activity during locomotion may correspond to those observed in invertebrates or lower vertebrates, and thus may have been partly phylogenetically conserved. Such an organization could support the dynamic control of posture by ensuring fluent movement during locomotion.

Anatomical optimization of skin electrode placement to record electromyographic activity of erector spinae muscles

Fine analysis of body movements is now technologically feasible, together with simultaneous recording of multiple muscle activity. This is especially true for the trunk and back muscles during human walking. However, there have been few anatomic studies of the area where deep back muscle activity is recordable by skin electrodes. We therefore attempted to optimize skin electrode location for recording erector spinae muscle activity at different levels of the back. For this purpose, 20 dissections of the posterior wall of the trunk were performed. The cutaneous plane was reclined on both sides to expose the superficial muscles of the posterior wall of the trunk. We dissected then plane-by-plane until we exposed the erector spinae muscles. The widths of the fascial spinal muscle insertions were measured at spinal levels easily identified clinically, i.e., C7, T3, T7, T12 and L4. Electromyographic assessment of the electrode location at these levels was performed in three subjects. Erector spinae muscle activity proved possible to record on several areas of the posterior wall through a superficial muscle aponeurosis. We propose a protocol for placing skin electrodes to record erector spinae muscle activity based on clinical anatomical references.

An examination of camptocormia assessment by dynamic quantification of sagittal posture.

OBJECTIVE Camptocormia is a disabling pathology of the axial system that debilitates patients in their daily life. To date, there have been no studies evaluating the impact of camptocormia on walking performance. This study presents a new method for assessing sagittal posture under walking conditions in patients with camptocormia. DESIGN The severity of camptocormia was evaluated by measuring sagittal inclination, represented indirectly by the horizontal distance between the C7 and S1 markers (C7 sagittal arrow; C7-SAR). Sagittal inclination was measured under various behavioural conditions using clinical, radiological and kinematic approaches. PATIENTS Forty-three patients were included in the study (17 with Parkinsons disease and 26 with idiopathic camptocormia). RESULTS Under static conditions, C7-SAR could be assessed using different methods. During walking, there was a dramatic increase in C7-SAR values. Correlation analysis revealed a relationship between functional impairment and dynamic C7-SAR values, but not with radiological C7-SAR values. PATIENTS with Parkinsons disease behaved differently from idiopathic patients, suggesting the involvement of different underlying physiopathological mechanisms. CONCLUSION Monitoring sagittal inclination during walking is more accurate than radiological measurements to determinine the detrimental effects of camptocormia and its consequences for quality of life.

Background summary: a new brace for the treatment of camptocormia

Methods Fifteen patients were consecutively included in the study. We excluded patients who refused to be equipped with a body jacket at the first consultation and who had lumbar pain when they were straightened up. Patients equipped with the brace were hospitalized for 5 days in order to learn a self-rehabilitation program. Evaluation at each visit included patient self-assessments, and physical and radiographic examinations.