The strength of a crab's claw is very important in determining which prey items are accessible to it.  If a crab can increase the strength of its claw, it can eat a wider variety of foods, which is important because of the migratory lifestyle of the blue crab.  I experimented with the response of crabs' claw strength to exercise--crushing glass vials with fish inside.  I measured strength in two ways; one, a simple fiberglass and spring machine which measured the force of a crab's pinch, and two, a bioassay of success rate in crushing a hard clam, measured on the first and last day of the experiment.  I found a statistically significant increase in the change of the total strength of the vial-crushing crabs, when analyzed for day by diet interactions.  Thus, vial-crushing crabs got stronger than fish-eating crabs.