Biomechanics of the back
The constitution and functions of the spine
The spine is the pillar of the skeleton. It is a long articulated bone stem, both strong and flexible, that connects the base of the skull to the pelvis. It supports the head, the ribs and indirectly the scapular belt. The spine is comparable to a mast because it helps to maintain the body's trunk by acting as a central stabilizing axis, supporting the body's weight and transmitting forces to the structures attached to it.
However, the spine does not stay rigid and its structure allows the man to be mobile, to be dynamic, to turn, to bend, to stretch and much more. A part of the spine is mobile because it consists of 24 vertebrae that are alternately interspersed with 23 intervertebral discs. The mobility of the spine is expressed in 3 natural curves: cervical lordosis, thoracic kyphosis, lumbar lordosis. The fourth curve, fixed, is formed by 5 sacral vertebrae and 2 to 4 coccygeal vertebrae fused together to form the sacrum and coccyx. Finally, the intervertebral discs act as a stabilizer of the spine because they absorb and distribute the pressures exerted on each movement in a regular manner. They give the column a high degree of mobility. The outer part is a flexible fibrous ring and it includes a pulpy and fluid core.
These natural curves of the spine allow it to ensure resistance and mobility.
The constitution and functions of the pelvis
The pelvis, or pelvic belt (from the Latin pelvis), is a bone belt between the spine that it supports, and the lower limbs on which it rests. It is composed of the sacrum and coccyx as well as two iliac bones, resulting from the fusion of the ilium, ischium and pubis. Sacroiliac joints allow the junction between the sacrum, which is a part of the spine, and the two iliac bones. The lower limbs join the pelvis at the level of the coxofemoral joints. The ischio-pubic branches (pubic and ischium branches), and more particularly the ischiatic tuberosities, allow the body to support its weight in a seated position, like a boat's hull. This is the main role of the pelvis, whatever the position of the body is.
Analysis of the sitting position
The coxo-femoral joint only allows a certain degree of hip flexion due to a lack of flexibility of the hamstring muscles, the tension of which restricts the movement (Todd et al., 2007),whereas the upright sitting position requires an angle of 90° between the trunk and the thighs. So the pelvis does a retroversion to compensate the limited hip flexion. Since the spine is directly attached to the pelvis, the retroversion of the pelvis causes a flattening of the lumbar curvature at the 4th and 5th lumbar intervertebral discs. In other words, the lumbar spine is the weakest link in the spine because it supports the most pressure. In the seated position, only 60° of flexion comes from the hip joint while the remaining 30° comes from a flattening of the lumbar curvature. The spine at the lumbar level is not that flexible. In fact, it is based on the pelvis as explained above. It is therefore from the pelvis that all the movements of the spine start.
Note: When the pelvis is retroverted, the lumbar pressure increases by 40%!
Soft tissues ensure support and mobility
The dorsal muscles are incredibly complex with four layers of more or less deep muscles. Some muscles stabilize the spine in an upright position, others are there to ensure its mobility. The muscles of the legs and pelvic girdle make it possible to mobilize the femur but also the pelvis, which has a direct impact on the curvature of the spine. In fact, the contraction of the hip and thigh muscles makes the pelvis tilt to anteversion or retroversion and so modifies the curvature of the spine (Todd et al., 2007). It should be noted that the ilio-psoas muscle is directly responsible for the lumbar curvature because it is attached to the lumbar vertebrae and the femur. The tilting of the pelvis depends on the distribution of muscle tension between the anterior and posterior muscles of the hip and thigh.
Man, a living being born for movement
There is no position that can be maintained for a long period of time with a feeling of comfort. When a static position is maintained, approximately 50% of the body's muscles contract to keep the body stationary and at the same time resist Earth's gravity, and the resulting static forces are much more challenging than dynamic movements (Todd et al., 2007). Any prolonged posture results in static muscle effort and increased tension in the joints and adjacent tissues that can cause discomfort. The natural behaviour of human beings requires regular changes in posture. We even adjust our posture unconsciously while we sleep.
The BackJoy dynamic seats solve this problem of immobility thanks to their proprioceptive action which stimulates the deep muscles, thus making sitting time "active" by a muscular solicitation which naturally leads to the core back muscles strengthening.
Choose your BackJoy Dynamic Seat
The seats of the Sitsmart range are compact and lightweight. They are easy to carry and will follow you everywhere, but also allow you to do stretching exercises or to accompany you in your yoga sessions.
SitSmart Core range
The SitSmart Core range is wider and more ergonomic for a more intuitive use. Beyond its dynamic aspect, the comfort provided is immediate and ideal for a prolonged use.
The seats of the Sitsmart range are compact and lightweight. They are easy to carry and will follow you everywhere, but also allow you to do stretching exercises or to accompany you in your yoga sessions.Comfort
Time of use
The SitSmart Core range is wider and more ergonomic for a more intuitive use. Beyond its dynamic aspect, the comfort provided is immediate and ideal for a prolonged use.Comfort
Time of use
For all those who consider that seating comfort is not negotiable and who do not primarily seek the dynamic and revitalizing aspect of the SitSmart and SitSmart Core models, the ComfortSeat range provides an appropriate solution.Comfort
Time of use
The Care Range combines safety, postural balance and pressure point relief for people who are confronted with the problems of prolonged sitting in a wheelchair but also during the bath.Comfort
Time of use