The effect of loads carried on the shoulders

This work describes a way of measuring the forces acting on the shoulders when subjects carry a backpack. A frame pack was carried by 12 male subjects: 4 hikers, 4 occasional hikers, and 4 novices. They walked for 30 minutes on a 5% inclined treadmill at 3.6 km/h to simulate moderate hiking. The load was carried at T9 and was increased (10, 15, and 20 kg) after 1, 20, and 25 minutes. The data from force transducers placed on the shoulder straps were collected for 30 seconds at 100 Hz. Shoulder strain appeared to be the limiting factor in load carriage. The optimal carrying method depends on the person, but it has been shown that decreasing stride length and wearing appropriate footwear reduces the strain on the shoulders.

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.

[Comparative study of static curves of the human spine in vivo during exercise and stretching in men and women]

Comparative study of static curves of the thoracic and lumbar spine in men and women has been realized under constraints of compression by weightlifting and elongation by exercise to parallel bars. In two athletic practices, curves decrease their arrow, ending to a straighter and more rigid column. This behavior expresses muscular actions. The greatest amplitude of displacement, observed in female series, shows lesser muscular forces in connection with a poor practice of exercises of body building.

[Preliminary analysis of the modifications of spinal curves, in extreme amplitudes, observed in rhythmic and athletic gymnastics]

Trained users of Rhythmic and Athletic Gymnastic, present kinetic spinal vast extents. Analysis, with pasted cutaneous markers, shows that, according to the codified movement, various segments of the vertebral column are requested and realized important displacements. Nevertheless, to have an homogeneous attitude, some subjects request more either lumbar or thoracic segments, of both. To prevent frequent spinal pain, it is important to realize a preliminary subject selection using their total spine and to improve protection by adapted gymnastic.

A model of the human lumbar vertebral column: a preliminary study

Finite element modelling of the human lumbar vertebral column employs data-processing procedures for study of the linear and nonlinear elasticity of materials such as are currently used in mechanics or in civil engineering. Thanks to developments in computer science, requiring a close collaboration between doctors and engineers, we put forward in this preliminary study a linear computerised model of the lumbar column comprising 4824 meshes and 6813 nodes. By reducing the simplificatory hypotheses and integrating new parameters, this model as developed is capable of important clinical applications in surgery and ergonomics.

[Reliability of cutaneous markers in kinetic studies of the human thoracic and lumbar spine]

The use of cutaneous markers as an accurate method of measuring spine motion was studied in five cadaveric spine samples and two live subjects. The markers were placed on the skin over the spinous processes, a particularly suitable site in thin subjects for determining the displacement of the underlying skeletal segments because the deep layer of the skin is in adherence with their fibrous surrounding sheath. Fairly close correlations were obtained in the sagittal and frontal planes between the two sets of measurements. However in the transversal plane the technique is unreliable because of tightening of the skin.