During eccentric contractions, passive muscular tension
develops because of lengthening of extramyofibrillar elements,
especially collagen content in extracellular matrix and
titin (182). This augments the active tension developed by the
contractile elements, enhancing the hypertrophic response.
Both the amplitude and duration of excitation coupling is
determined by motor unit (MU) firing frequency, the extent
of which are believed to encode signals to various
downstream pathways including Ca2+ calmodulin phosphatase
calcineurin, CaMKII, and CAMKIV, and PKC (26).
These pathways help to determine gene expression, coupling
muscle excitation with transcription (182)