The most prominent decline in masseteric activity was recorded in patients aged 75 years and older, which might be due to the reduction in both tendon and superficial reflexes.
[6] A study also reports that 52% of the elderly exhibit an absence of jaw jerk reflex, in an average age of 81.8 years.
[7] Jaw muscles do not display very prominent changes in muscular tissue with age in healthy elderly, as their oral cavities are in constant motor movement (i.e.: performing tasks such as talking and chewing etc.).
This motion delays the decrease in lean body mass and aids protein retention that comes with age, preventing the muscular tissues from wearing and tearing.
In other words, a normal jaw jerk reflex points the diagnosis toward cervical spondylotic myelopathy and away from MS or ALS.