Lumbar range of motion1/6/2024 Even when the powerlifters were in global full flexion, the individual lumbar segments were not in full flexion and remained in the neutral zone to protect the spine. The work by Cholewicki and McGill on powerlifters with fluoroscopy showed that the active system prevents the spine from entering the elastic zone. In the elastic zone or at extremes of motion, there is likely a chance of injury when the spine is loaded. Maintaining the spine in the neutral zone is important to prevent injury. Also, the evidence suggests that the weakness of muscles can lead to segmental instability and cause back pain even in the absence of structural defects. Measures of lumbar lordosis, pelvic tilt, and leg length discrepancy, which measure the passive system does not seem to be as important as muscle strength and endurance, which are measures of the active system. The importance of the active system becomes apparent when attempting to link between clinically measurable parameters and back pain. These factors contribute to endurance to maintain stability over long periods of static postures and increased strength when the spine is subject to suddenly increased stress like a fall or a sudden loading of the spine: both muscular strength and endurance decrease in patients with low back pain. Muscles provide stability in the neutral zone. Both strength and endurance are equally important. Hence lumbar stability is the ability to maintain the spinal neutral zones during routine functional activity without causing the neurological deficit, significant deformity, or incapacitating pain. Because of the increased stiffness at the end ranges of movement, the load-displacement curve of the spine is non-linear with increased flexibility around the neutral position of the spine and increased passive resistance and decreased flexibility in the end ranges of motion. At the ends of the range of motion is the elastic zone, where the stiffness of the system increases. There is very little stiffness of movement within the neutral zone. The neutral zone is the normal functional range of movement. The range of movement in the spine can subdivide into a neutral zone and an elastic zone. In a healthy state, if the three systems interact and provide stability, then following injury or degeneration to the passive system, the active system needs to work harder to compensate for the decreased contribution from the passive system. Based on this, clinical instability can be defined as the abnormal displacement that occurs within the motion segment when a normal physiological load is applied. Īn inability of the active system to maintain the relationship between different elements of the passive system during physiological loading can lead to spinal pain. The neural system should act at the right time and the right amount to protect the spine from injury and to allow the desired movement. The neural control subsystem receives input both from the passive and the active subsystems and then direct the spinal musculature to stabilize the spine. Cadaveric experiments show that when the muscles are removed, and only the bones, discs, and the ligaments are left in situ, the spine buckles under low loads of 20 lbs (9 kg). The contribution of the passive system in the neutral spine is minimal. With stress loading of the passive system (vertebrae, disc, ligaments, and joints), the active system (muscles) come into play and prevent abnormal deformation. In a normal healthy spine, the above three systems interact and allow normal function and a pain-free range of movement. The neutral system that interacts between these two systems
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