Adverse changes in fibre type and myosin heavy chain compositions of humanjaw muscle vs. limb muscle during ageing

This review shows that human jaw muscles not only have unique fibre type an d myosin heavy chain (MyHC) compositions but also undergo muscle and region -specific changes in fibre composition during ageing. Alterations in the ma sseter and the lateral pterygoid muscles in the elderly are opposite to tho se reported for limb and trunk muscles, whereas changes in the anterior and posterior bellies of the digastric muscle resemble those of limb and trunk muscles. We conclude that age-related alterations in fibre type compositio n and MyHC expression are muscle and region specific, probably reflecting m uscular differences in genetic programs and epigenetic influences.