In the sliding filament model of muscle
contraction, the (thin) actin myofilaments [red] (attached to the Z-line) slide (actually, are
pulled) inward along the (thick) myosin myofilaments [blue], and the
sarcomere (measured from one Z line to the next) is shortened.
Note on the measuring scale that as contraction is occuring, both
the sarcomere length and the I band (area where thin filaments
do not overlap with thick filaments) length decrease, but the
A band (area containing thick filaments) length remains constant.
animation ©1998 Mark Meyer / 3 Dot Studio