The low back acts as the shock absorber for the trunk, and the neck absorbs the shocks for the skull, but there is little to no shock absorbancy for the Jaw. This means that the pounding of the pavement can directly impact into the friction-reducing discs inside the jaw joint, leading to exercise-induced TMJ syndrome.
The neck tries to nod the head in time with the wagging of the jaw, creating tight sore muscles as well as overloading the co-ordination centre. This condition is seen in high-performance elite athletes as well as those who run recreationally - in fact, it's more commonly seen in patients who have recently picked up the 'healthy habit' of 5 Km a day, as their bodies are yet to become accustomed to this new level of exercise.
The tight muscles in the upper neck and jaw can create toothache, headaches, creaking and popping jaw sensations as well as generalised neck stiffness and aching shoulder muscles. Before you reach for the painkillers, try gently stretching out the neck muscles whilst yawning - opening the mouth as wide as it will go. These aches and pains are only temporary - your neck is getting some exercise too - and it's no reason to splurge on a new pair of running shoes, as the shockwave from the heelstrike maintains bone density. Just make stretching out the neck and jaw part of your post-exercise stretching regime, and use ice on the back of the neck to reduce any residual tension.
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