few other things...
calcium is released from the sarcoplasmic reticulum, and then relaxation occurs when calcium is pumped back into the sarcoplasmic reticulum. So if calcium unable to be released or unable to be pumped back, then there's going to be a problem.
then some people don't like learning like this, but H and I are the important things to remember (both get smaller during contraction)
myosin, longer word, thicker fragment- H zone, only myosin (thicker letter)
actin, shorter word, thinner fragment- I band, only actin (thinner letter)