This is my first attempt to write an article that deals with physical aspects of driving -- operating the machine behind the machine. I.e. the human body of the driver. Driving has been invented to avoid the physical effort and waisted time in walking and more archaic transportation devices (cycling, etc...), but it involves some important physiological aspects.
A proper driving position yields several ergonomic advantages. The driver's seat is constructed to support the spine along it's S-shaped formation. To do this, we need to avoid the slumped driving position adopted by drivers by tilting the pelvic forward to put pressure on the lower back. Squeezing the rump as snugly into the seat as possible allows for maximum support the back and hips.
All other ergonomic adjustment of a seating position are derived from this one. In driving our body encounters physical forces that might make it slide from the seat, and likewise or limbs need to be bent forward to operate the steering and pedals. We need to ensure that even under the most extreme of these conditions - the friction with the seat is maintained.
For the pedals, this is achieved by ensuring that even under full pedal travel, the legs are not fully outstretched. A "hyper-extended" lower extremity would mean that all the muscles of the leg have been fully deployed, and cannot be used to apply strong pressure to the pedal when quick braking is required, for instance. This kind of leg position is also orthopedically hazardous in a collision. The driver will instructively push back and "lock" his knee so that the muscles limit the ability of the knee to bend, so that instead of folding in a collision, the knee suffers from fractures. Also, the energy of the impact, otherwise absorbed into the muscle tissue, will be transmitted directly through the bones, projecting the orthopedic injury to the hips and possibly the base of the spine.
For the steering, a similar result is achieved by adjusting the back and steering so that they are as parallel as possible. There will always be an angle between the two, which has to be compensated by bringing the body closer to the wheel or bringing the wheel towards the body. If the wrist can rest over the top of the wheel - which is furthest from the driver, the hands can grip the wheel anywhere, including on the "wrong" side, without outstretching the elbow or making unnecessary back movements (leaning forward).
Outstretching the arms limits the ability to turn the wheel into merely a function of the shoulder muscles (mainly the deltoid), reducing the sensitivity and increasing physical effort, as well as risking fractures in the arms and scapulae in a collision. Leaning the back forwards is hazardous because the weight of the back will be leaned against the steering, making turning the wheel harder and making side forces of cornering rock the body sideways, making our weight rock the wheel.
Once adjusted, a proper placement of the hands should allow steering control and proper utilization of arm strength. The first point is to utilize all potential leverage by placing the hands as apart as possible, at 9 and 3. Any higher or lower will make the hands closer, so they work more like one big hand rather than two separate arms.
When turning the wheel like this, the weakness of one-handed steering is revealed when gravity pulls the steering hand down, which would in theory make us turn the wheel more than wanted, which we naturally resist with lifting our hand with our deltoids, making it a greater effort. With both hands at both side of the wheel, turning the wheel 90 degrees, puts one hand on the bottom of the rim, under the full effect of gravity, while the other hand is directly on top of the wheel, being fully supported by the rim. Both hands as if balance one another.
The steering height and distance can also be used to maximize hand efficiency in this posture. As the hands reach shoulder height, it becomes easier to apply steering inputs because of greater leverage from the deltoid. However, this position also makes it harder to keep gripping the wheel statically at that position, because the shoulder get tired, which is why it is advisable to have the wheel adjusted so that it is gripped just below shoulder height.
The legs can also be used more properly when given attention. Lower body support can be achieved by using the dead pedal. Putting the left foot on it, rather than using it to brake or placing it over the clutch, places our legs in a wider base, supplying additional body support and a more equal distribution of the body weight over the sitting bones. It can also support the body by applying pressure against the footrest. Unless doing so, the tendency of our body to move (accelerate) forward under strong braking, will make us lean unto the steering wheel (Effectively killing all ability to veer while braking) and likewise against the brake pedal (making us apply unnecessary additional pressure).
The right foot can also be used more efficiently. Our heel needs to be placed on the floor so that the weight of the leg is supported by it rather than leaned on the pedals or against our muscles. We can than operate the pedals with the ball of the foot. When steering with our hands, we use our fingertips (Being the most sensitive part of our body, save the lips), but the foot is different from an anatomical perspective. The palm and fingers are a direct line stemming from the forearm, allowing us to use the forearm muscles to operate our digits. The foot, however, is perpendicular to the crus, and using the toes reduces our leverage. Also, when pressing forward, the toes can be titled back or slide down, making it harder to apply precise pressure onto the pedal.
The pedal formation is designed so that the driver can pivot over the heel, which remains stationary and roughly in front of the brakes, and lean his foot (by use of the thigh rotator muscle), and operate the throttle. This makes most people press the throttle close to the lower portion of the pedal. This is advantageous because it makes the driver apply pedal pressure through the smaller muscle groups along the ankle (hamstrings mainly), rather than the bigger muscle groups of the leg itself (quadriceps), making it more sensitive. The pivoting motion allows quick access to the brakes.
Steering techniques allow to utilize the strength of the arms more wisely. We can define the steering motions as "push" and "pull." In general, it's best to use both hands symmetrically, but this is not always best because the forearm end up crossing over. For large amplitudes, we prefer pulling over pushing. Pushing is done by using the deltoid, trapezium, pectoralis, etc...These are strong, large muscles that are not good for fine motor skill and result in too much effort for otherwise easy tasks. Pulling uses the muscles of the arm itself: biceps, triceps, but mainly the forearm muscles, which are smaller and provide a fine motor skill by operating the digits.
This advantage is somewhat compromised when we pull down towards the bottom of the wheel. At that point, we rotate the forearm in a manner that makes us utilize the biceps strength and also bend our wrist, which narrows the carpal tunnel hosting the median nerve. The solution is to place the hand across the wheel and pull it from across and over.
Energy management is a manner of metabolism, cardiovascular function, etc. Improving our energy management allows to endure loads of performance driving or maintaining free limb motion and concentration in long road drives, and avoid "energy drains." In terms of training, the method that achieves such endurance is "strength drills" like free-weight lifting, particularly in "super-set" form. Another method is better nutrition, through consumption of natural compound carbohydrates, found in fruit and whole grain, which is translated into Adenosine Triphosphate, producing muscular energy).
If we consume artificial carbohydrates (sucrose sugar), fats or too much of either -- we rush our metabolism. I explain: Carbohydrates are essentially sugars, which are dissected into glucose (further dissected into ATP) by streaming insulin into the bloodstream through the pancreas. We can only absorb as much sugar as our pancreas allows. Too much makes us compensate by streaming insulin which makes the glucose be process in a rushed matter. Too much sugar or artificial sugar consumption therefore results in a sharp "peak" of energy follows by a sudden drop. It's important to mention that this "sudden" peak does last for one or two hours, which can be good for a racing session or a moderately-long drive.
In heat or demanding performance, we also suffer from sweat which makes us lose water in a pace greater than that of urination (which is why racing drivers almost never need to pee mid-session), but likewise makes us lose minerals. If we only drink water to compensate for what we sweat, we will not get the proper electrolytes, thus suffering from acute headaches. It is therefore customarily to consume enriched fluids, which can be artificially created by mixing water with any kind of juice (one liter of water with a liter of juice) and a spoon of salt. For carbohydrates and protein, we need to balance our loses by taking an energy bar (a banana can also do) once every hour or so.
Alcohol consumption is of course a problematic issue. Alcohol is essentially a toxin that, like all other toxins, is being processed in the liver uses a protein called Alcohol Dehydrogenate to mix it with oxygen and form a substance called Acetaldehyde (CH3CHO), which causes the sickness, sweat and redness, caused by flexing artery walls. Consuming alcohol faster increases the effect, as does holding it in the mouth (where some initial absorption occurs).
The time for alcohol to wash out of the blood stream depends on body weight, mainly on tissues that can absorb it. Women have a lower percentage of water in the body (about 50%), thus being more prone to intoxication. As a rule of thumb, darker liqueurs, ales
and red wine -- carry larger percents of alcohol. Food helps to reduce the alcohol concentration in the stomach, but coffee only effects the symptoms of intoxication.
It's important to stress that the effect of fatigue is similar to that of intoxication. Temporary solutions like opening up a window or using the radio to keep you up are only temporary. The real solution for driving when very tired is to find a SAFE place to stop and sleep. As a rule of thumb, 30 minutes worth of slumber gives you 55 minutes of wakefulness. Younger people or athletes need more sleep than others.
The other end of the physiological aspect of driving is injuries inflicted in collisions. The first kind of injury is defined as a "direct" impact, which is a result of hitting something solid. These kind of crashes are prevented by: seating in the seat, being harnessed by the seatbelt and stopped by the head-restraint and airbags, as well as internal padding. It is in fact rare to see such damages in modern cars when they crash.
The other kind of impact is internal injuries caused by the sudden deceleration of the car. As the car decelerates, our internal organs seek to maintain motion. This is relevant mainly to our sensitive brain, as well as to the internal parts of our abdomen and the relevant blood vessels. These clash against the skull and the wall of the gut. The most common injuries are internal bleeding in the petronium, head concussion, and punctured spleens. The prevention of such injuries is generated by designing crumple zones into the chassis, allowing the physical force of the crash to be diverted around the protected passenger compartment.
The above description assumes a proper driving position which allows to utilize the car's safety installments to the driver's advantage. If the head-restraint is too far from the head, it will result is the head being flung backwards and forward, extending the spine to result in whiplash. If too low, the head-restraint itself will in fact magnify the problem by applying pressure unto the lower cervical vertebrae, or even breaking the neck.
Likewise, too leaned a back rake will result in submarining under the lapbelt. The knees would clash against the underdash while the upper body be thrown in all directions, to suffer injuries to the shoulders, head, neck and upper back. Submarining, as well as an improper location of the lapbelt on the soft belly instead the hips, would result in aggravating the internal abdominal injuries.
Too close a position to the wheel, particularly when the breastbone (sternum) is under 10" away from the wheel, results in contact of the sternum and head with the airbag as it still deploys at 320km/h. This is the equivalent of hitting a brick wall at 35km/h, and the severity increases with speed. A proper seating position as well as wearing a seatbelt, prevents this injury. Too high a hand placement on the wheel, can project the hands into the driver's face or into the face of the passenger, while proper hand placement should make the airbag (which opens in some sort of triangular pattern) force the hands down against the thighs.
The diagonal part of the seatbelt belongs directly onto the acromion, and not (as people believe) on the collar bone itself. The collarbone is quite thin and will fracture once the belt is used. There is an additional risk of the belt chafting against the throat, causing cuts. Placing it on the acromion puts it on a strong bone formation, from the shoulder down onto the sternum. Too low, on the shoulder itself or on the arm, will hinder steering and will cause the belt to slip off as the body is "rotated" around it during a crash. Placing the belt even lower, and under the armpit actually allows the belt to operate properly, but in the price of having it injure the arm or even dissect it fully.
Child restraints are meant to replace or back-up the seatbelts which are intended for grown humans, which are tall enough and have tough bones. Babies in particular suffer from a big head and a feeble neck, forcing us to place them against the direction of travel, to avoid the forward motion of the head in a crash. Once grown up, a booster is used simply to keep the child in the appropriate height so the lapbelt runs over the hipbone and the diagonal belt runs over the acromion.
Lack of wearing seatbelts not only results in hitting solid objects (mainly the underdash), flying out of the car, or hitting airbags as they still inflate, but also make the body of the unrestrained passenger rattle about in the vehicle, hurting other passengers, particularly the one seating in front of the unbelted passenger. The same goes for child restraints which are not properly harnessed by the belts or ISOFIX, which are projected with the child in an accident.
Other injuries include a sideways jerk of the neck, and a potential impact with the window or upper door seal. This is reduced by curtain airbags, and a proper height of a seating position. A half-opened window is particularly dangerous, as it's sharp topmost portion can hit the side of the head quite forcefully. Other injuries include small glass shards of untempered glass, from aftermarket mirrors or screens inside the car, and even smaller shards that go into the eyes and face.
Done. My point was to survey what I believe is a neglected realm in the world of driving. This is one article of a line of articles which will also touch psychological elements, and physical aspects of car design and road construction.
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