Medical Logistics - Army Logistics University - U.S. Army

At left, the seat adjustment has the Soldier’s hip and knee at the same height. At right, a Soldier sits
in an M1114 seat with his knees higher than his hips. Both of these positions can cause back injury by
decreasing the lumbar curve and the spine’s ability to absorb shock while the vehicle is in motion.
long-term pressure on these nerves causes chronic
lower back pain.
With assistance from the 336th Transportation Group’s
safety officer, several vehicles used by these Soldiers,
including the heavy equipment transporter (HET), M915
tractor, 5-ton truck, and M1114 high-mobility multipurpose
wheeled vehicle (HMMWV), were examined
for postural supports. The key factors determined to
contribute to lower back pain included—
• A poor relationship between the hip and knee
height of the driver.
• Low seats.
• Poor curvature of the lumbar spine.
• Excessively reclined backrests.
Once these factors were corrected, drivers typically
reported decreased lower back pain.
24
Sitting Correctly in Vehicles
When seated, the driver’s knees should be lower than
his hips. The relationship between hip and knee height in a
seated position often determines the presence of a natural
curve in the lower back. When the hips are equal in height
to the knees, the curvature of the lower back is reduced
and the Soldier experiences a “slouch” in the lower back.
This can occur when the driver seat is adjusted too low.
A good example is the rear seat of an M1114, where the
low seat combined with the lack of leg room results in
the knees resting well above the hips. Curvature of the
back in this extreme position is relatively nonexistent, and
excessive pressure is placed on the discs of the lumbar
spine, causing Soldiers to experience pain after prolonged
periods of riding. The seat height should not be lower than
the height of the lower leg of the person in the seat.
NOVEMBER–DECEMBER 2008