A car headrest is not designed to rest your head against and relax while driving. It is actually a head restraint, designed to prevent a whiplash injury in a rear-end collision.
Federal Safety Regulations now require the head restraint to be a distance of 2.2 inches or less from the back of the driver's head. Compliance by car manufacturers began September 1, 2009, under a phase-in schedule that required all new vehicles to meet the new head restraint regulation by September 2010.1 Unfortunately, the head restraints of these newer vehicles are positioned too far forward for many drivers - actually pushing the driver's head forward, resulting in neck/back pain, headaches, and driver distraction.
In general, the drivers most affected by the new forward head restraint design are:
The forward head restraint design will also be more of a problem in car seats where the backrest has excessive concavity and/or softness in the mid-back region. As the driver's thoracic spine and rib cage sink into these backrests, the relative head restraint position will be moved further forward.
A lack of knowledge regarding healthy and safe driving posture resulted in a major error in the positioning of these new head restraints. This is reflected in the measurement methods of the Insurance Institute for Highway Safety (IIHS) for determining the horizontal distance between the head restraint and the back of the head. For this measurement, the test dummy (called the H-point machine) is positioned on the car seat at a trunk recline of 25° from vertical. 2 The IIHS considers this trunk recline of 25° "a typical seatback angle" when driving.3
However, when driving with a trunk recline of 25° from vertical, the head and neck are brought forward from the reclined trunk to achieve proper visibility out the windshield. This postural distortion is reflected in the IIHS testing, with a 25° trunk recline, but a vertical position of the head/neck segment of the test dummy. As a result of this postural distortion with a 25° trunk recline, the head restraint needs to be positioned a significant horizontal distance forward from the backrest, in order to be close to the back of the driver's head.
Besides distorting one's driving posture, a 25° trunk recline relaxes the trunk musculature, resembling the trunk instability of an unconscious person. The increased reaction times at the foot pedals with a relaxed core can have serious implications when trying to avoid an accident.
As mentioned earlier, the healthiest and most alert driving posture is with a slight trunk recline of 5° to 10°. Without the forward postural distortion of the head and neck characteristic of a 25° trunk recline, a slight trunk recline of 5° to 10° will require a head restraint positioned less further forward from the backrest. With a slight trunk recline, drivers with a thinner torso have the greatest risk of the head being pushed forward by an extreme forward head restraint designed for a 25° trunk recline. The healthiest solution for correcting an extreme forward head restraint is adapting the backrest to provide lower thoracic support, thereby elevating the rib cage, elongating the thoracic spine, and moving the upper trunk slightly forward. With the proper thickness of the lower thoracic support, the head and neck are positioned in a stress-free upright posture, with very slight clearance of the back of the head from the excessively forward head restraint.
The addition of lower thoracic support also requires the addition of sacral support to properly stabilize the pelvis with movement of the vehicle.4, 5 The resulting active-alert driving posture with lower thoracic support, sacral support, and a slight trunk recline (5° to 10°), called The YogaBack Posture, optimizes trunk stabilization and diaphragmatic breathing, with faster reaction times at the foot pedals.6
The addition of lower thoracic support and sacral support is the most effective way to prevent a slumped driving posture. This has important implications for a whiplash injury, as backward bending of the head is almost impossible when slumping. This severely restricted backward head movement with a slumped driving posture may explain why a whiplash injury can result from a slight rear-end impact! 7, 8
For future head restraint design, besides height (vertical) adjustability, depth (horizontal) adjustability is just as critical.9, 10 With proper depth adjustability to the head restraint, many drivers will no longer be forced to distort their posture and compromise their safety, in order to conform to the auto industry's erroneous concept of healthy and safe driving posture.
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