Researchers at the University of Pennsylvania, in collaboration with those at the Marine Biological Lab in Massachusetts, US, have worked out the mechanism behind the fastest muscle among vertebrates. The toadfish's swim-bladder muscle contracts and relaxes 200 times per second as it makes its mating call, compared to 0.5-5.0 hertz for the its locomotary muscles. It is reported that calcium, which triggers contraction, cycles through the bladder muscle 50 times faster than in locomotary muscles ( Science ,