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Transcript of The Spine
stack of 33 vertebrae
sacral (5 - fused)
coccyx (4 - fused)
90% water in young, healthy discs
discs dehydrate during periods of extended loading, which is why you get shorter during the day
after childhood, discs rely on mechanical action to transport nutrients and wastes, so occasionally changing postures is a good thing
L5-S1 subjected to the greatest loading
curvature of the spine
movements of the spine
all three planes, plus circumduction
flexion and extension
don't confuse spinal flexion with pelvic tilt or hip flexion
muscles - paired on left and right side of the body
bilateral activation = flexion/extension
unilateral activation = rotation
back extensor muscles:
almost always active during standing
COG is anterior to spinal column
generates rotational torque on spine, counteracted by extensors
extensor muscles moment arms are very small, so large forces are required
results in large compressive forces in spine due to muscle activity
loads on the spine
loads increase when you move from standing to sitting and from an erect to a position of spinal flexion
both compression and shear forces
anteriorly-directed shearing forces are associated with back injuries
lifting heavy objects:
lateral flexion and rotation generate huge compressive forces in the spine
50 Nm of torque = 800 N of compression
50 Nm of torque = 1400 N of compression
50 Nm of torque = 2500 N of compression
DON'T LIFT WHILE TWISTING!
LIMIT ASYMMETRICAL LIFTING!
rapid, jerky movements increase compression and shearing forces
DON'T JERK THE OBJECT!
unless this helps get you quickly get into a more stable position
maintaining normal lumbar curve allows:
extensor muscles to partially offset the anterior shearing forces
uniform loading of lumbar discs
lordotic posture increases posterior annulus and facet joint loading
lumbar flexion prevents extensor muscles from effectively counteracting anterior shear
MAINTAIN NORMAL LUMBAR CURVATURE!
helps stiffen trunk and reinforce spine against compressive loads
increases ability of extensor muscles to overcome flexion torque from body weight and resistance load
TAKE A DEEP BREATH!
flexion relaxation phenomenon
spinal extensors resist flexion until full flexion is reached, when they stop developing tension
spinal ligaments are then totally responsible for stabilizing flexion torque
in full flexion, spinal ligaments add to the anterior shear force and facet loading
repeated flexion increases extensor relaxation period, reducing lumbar stability
LIMIT REPETITIVE LIFTING WITH SPINAL FLEXION!
low-back pain risk factors:
increased flexion torque
degenerative effects on discs
working with unnatural posture
working with sudden, unexpected motions
sitting for prolonged periods or standing for prolonged periods
working with dynamic motion in multiple planes
fatigue of spinal extensors
low back pain
2nd leading cause of missed work in U.S.
most common and most expensive of all worker's compensation claims in the U.S.
but don't hold it for more than ~2 sec...