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- isotropic band is designated the I band;
- this is composed of thin filaments - composed only of actin;
- at higher magnification, each I band is bisected by a dark line, Z line;
- a sarcomere, extends between two successive Z lines & is approximately 2.2  long in resting muscle.
- w/ max contraction, sarcomere shortens 20-50% of its nl resting length.
       - I band becomes shorter & H zone usually disappears.