Simply doing your normal speed drills with an aquabag on your shoulders will improve your speed.
By adding an unstable load (eg: aquabag) to your shoulders, your body naturally responds by co-contracting key muscles acting around the spine, so as to produce a “stiffer” body, and hence better force transfer.
Make sure you do not “over-fill” the aquabag. The water needs to move a lot to create the unstable stimulus. Between 5-11kg of water in a
large sized bag is good for speed drills.
You also need to hold the bag firmly, so that the movement of the water is traferred directly to the body. This maximises the stabilising response of the body.
Simple. Effective. Fun.