G. Poumarat

Changes of contour of the spine caused by load carrying.

The development of new leisure activities such as walking has spread the use of the backpack as a means of carrying loads. The aim of this work was to present a way of defining the movements imposed on the trunk by this type of load carrying. A 20 kg load situated at the thoracic level (T9) of the trunk, was placed in a backpack (2.5 kg). The 12 subjects were average mountain guides of Auvergne region, intermediate level and complete beginners. External markers were glued to the projecting contours of the spinous processes of the C7, T7, T12, L3 and S1 vertebrae, the shin and the external occipital tuberosity (EOT). Using a Vicon 140 3-D system we measured the effective mobility of the different spinal segments in the sagittal plane during one step. For every subject, we noticed a significant decrease of the effective inter-segmental mobility (EISM) between S1-L3-T12 (p < .01) while backpacking a 22.5 kg load. A decrease of EISM also appeared at the next level between L3-T12-T7 (p < .05). An increase of the EISM between T7-C7-EOT was noted (p < .05). We supposed that strength loss of the back muscles and/or angular oscillations of the trunk could be a common cause of symptoms during backpacking. The subjects using this type of load carrying have to adopt an adequate position of the lumbar, dorsal and cervical vertebrae.

Influence of the mode of load carriage on the static posture of the pelvic girdle and the thoracic and lumbar spine in vivo

The influence of various modes of carrying a load of 16kg (15.69DaN) on the static positioning of the pelvic girdle and the thoracic and lumbar segments of the spine was examined in seven male subjects. The displacement of cutaneous markers attached to easily palpable skeletal landmarks was recorded using 4 CCD cameras the data acquired were analysed using an optoelectronic technique (SAGA3). The subjects stood upright on an AMTI biomechanical force platform, from which the ground reaction forces enabled displacements of the centre of gravity axis and thus the moment of the mass carried to be determined. The modes of load carriage examined were 1) in a case in the left hand 2) in a case in the right hand 3) equally in two cases 4) on the head 5) in a rucksack and 6) in an anterior bag. The results showed displacements of the pelvic girdle, the caudal and cranial lumbar segments, and the caudal and cranial thoracic segments in the three orthogonal planes (sagittal, frontal and transverse). The influence of the moment created by the load was seen in the statokinesigrams. The use of external markers using an optoelectronic technique, in association with the ground reaction forces, enables the mode of load carriage to be determined. The results show that the influence of the moment exerted by the mode of load carriage on the gravity axis has important ergonomic consequences.

Determination of the position of the pelvic girdle using surface markers.

The overall movement of the trunk is made up of two components, namely the movements of the pelvic girdle and the vertebrae. In the frontal plane, the amplitude of the pelvic movements appears to be relatively limited compared to the vertebral column whereas the pelvis makes the major contribution to the total rotational movement in the axial plane.

Role of hip abduction in the kinetics of the thoracic and lumbar spine

Summary The motion of the thoracic and lumbar spine segments was analysed by mean of the skin landmarks method in 14 volunteers (7 males, 7 females). The results demonstrated that there was no significant difference between men and women and there was either facilitation or limitation of the motion of the characteristic landmarks of spinal segments during trunk motion in perpendicular planes. The mobility of spinal segments was associated with pelvic girdle motion in order to obtain the planned amplitude, and varied with hip joint abduction. The analysis of the precise mechanisms of relaxing or stretching of the pelvivertebral musculo-ligamentous structures constitutes a large field of investigation that necessitates the study of other lower limb postures and the use of robotic techniques.