Stroke length and swimming speed

Swimming speed is determined by two factors, stroke rate (SR) and stroke length (SL). SR is represented as the number of strokes a swimmer takes per minute and as you have already found out reffers to how fast you can move your arms. This is something that is predermined due to hereditary factors and it takes very little improvement through training. The other factor that determines swimming speed is SL which refers to how far your body travels during each stroke cycle and not how far your hand moves. What a swimmer does between strokes affects SL more than how he pushes the water back. Thus minimizing drug will improve SL far more than an increase in propulsion.