A coach stands on the deck and tries to teach stroke technique while not being able to see exactly what the swimmer is doing underwater. Even worse, swimmers never see their stroke either, and just assume they are doing what their coach has told them. In addition, stroke instruction is based on subjective opinion. Some coaches prefer this theory, some that.
Nothing is measured.
Since each stroke in swimming is less than one second, you can imagine the difficulty of training a large group of swimmers while standing on the deck, unable to see what is happening underwater. As a result, most swim training is just training, with very little instruction. Swimmers get faster as a result of ever increasing yardage, greater intensity of training, and weights. This unusual program grew out of 1500 hours of research Somax has conducted since 1985 on underwater tapes of World Record swimmers, as well as measuring many Olympic swimmers and training 17 elite swimmers. Many of our findings were at variance with wide-spread assumptions about swimmers and swimming.