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Unloading of Spinal Discs
Human spinal discs have viscoelastic properties. That is, they compress at a decelerating rate when loaded and expand at a decelerating rate when unloaded. Higher loads result in a higher rate of compression. Spinal loading from daily activities will cause shrinkage in stature, of up to 20mm over the day. (Astronauts are up to 2” taller when they return to earth, than they are when they leave!)
This transfer of fluid in and out of the disc is the body's mechanism for supplying nutrition to the discs. Spinal discs do not have a direct blood supply, and this osmosis and diffusion is essential to maintaining spinal health. It is unknown how often the spine needs to be 'unloaded' during a day to maintain good disc health. Of course, disc fluid transfer is also increased with movement (that is exercise!)
Given that the onset of degenerative spinal changes occurs is commonly at a young age in industrialized societies such as our own, and that these degenerative spinal changes occur only at more advanced ages in primitive societies, it is likely that we need much more unloading and/or exercise in our daily lives than we currently get. Loads on the lumbar spine are reduced in neutral lumbar postures. Technically speaking, the neutral posture is defined as being near the mid-point of the available range-of-motion in that body region.
Relaxation of Spinal Muscles
The heart pumps blood, full of nutrients and oxygen, to our body parts. Muscles 'pump' blood, carrying the waste products of metabolism, back to the heart. The muscle pump works by massaging the blood vessels which pass through them. The pumping massage action occurs as the muscles intermittently contract and relax. During sustained muscle contractions, blood flow through the muscles in restricted or occluded. So it is important the the muscles have intermittent opportunities to relax. (For references, check any basic physiology text)
The Zero Gravity recliner reduces spinal loads and allows muscles to relax in the following ways:
1. Thigh-Torso Angle
a. The lumbar spine achieves a neutral posture with a 125° -135° thigh-torso angle. The relationship between lumbar neutral positioning and the thigh-torso angle varies among individuals and also upon whether the individual is in a no-weight bearing posture.
b. In sitting postures, lumbar disc pressures decrease and back muscles relax more with larger thigh-torso angles.
2. Reclined Postures
a. Lumbar disc pressures decrease as the torso moves from the erect posture to a reclined posture. When backrests are used, part of the body weight is transferred to them when a person leans back, reducing the load on the lumbar spine caused by the upper body weight.
b. Back muscles relax as the torso moves from the erect posture to a reclined posture.
3. Lumbar Support
a. Lumbar disc pressures decrease in the presence of a lumbar support. The decrease is greatest when the lumbar support is placed at the 4th or 5th lumbar levels. The us of a lumbar support changes the posture of the lumbar spine toward lordosis and hence reduces the deformation of the lumbar spine and corresponding disc pressure. The effect of the lumbar support is greatest when the thigh-torso angle is smaller, so this in unlikely to be a significant benefit in the Zero Gravity Recliner, as the recliner positions the user in larger thigh-torso angles
Contact us to let us help you identify the right Zero Gravity Recliner for you!