I don't know of any clear evidence that this is trainable. Very recent research in molecular biology have isolate the basic biological motors that produce muscle contraction. This correlates well the macroscopic measurements of muscle contraction. It appears that the muscle speeds are set by the basic biological motors. See article in Reviews of Modern Physics on molecular motors, the ultimate determining factor on muscle contraction.
Tendons can have very fast contraction times.
Nerve Conduction Velocity From head to muscle. Fast with big nerves and slow with small peripheral nerves. Shorten the path for fast response. Reduces nerve conduction velocity Frequency of signal. High Frequencies cause higher contraction rates.