Changes of contour of the spine caused by load carrying

The development of new leisure activities such as walking has spread the us e 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 t runk, was placed in a backpack (2.5 kg). The 12 subjects were average mount ain guides of Auvergne region, intermediate level and complete beginners. E xternal markers were glued to the projecting contours of the spinous proces ses of the C7, T7, T12, L3 and S1 vertebrae, the shin and the external occi pital tuberosity (EOT). Using a Vicon 140 3-D system we measured the effect ive mobility of the different spinal segments in the sagittal plane during one step. For every subject, we noticed a significant decrease of the effec tive inter-segmental mobility (EISM) between S1-L3-T12 (p < .01) while back packing 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 durin g backpacking. The subjects using this type of load carrying have to adopt an adequate position of the lumbar, dorsal and cervical vertebrae.