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.

It makes sense that a longer stroke would consume less energy than a shorter one, but in water the efficiency of a longer stroke is especially valuable. First, there is the energy cost of a higher SR. When you double your SR, you burn energy four times faster. Second, a higher SR - and the higher heart rate it brings - hurt your form. As SR and heart rate increase, your stroke becomes more ragged and energy cost increases even more. And finally, you create far more turbulence when stroking at a high rate.

There are a few advantages in improving your SL instead of your SR and these are that in SL you use your knowledge, body awareness, and concentration to maintain sleek, efficient positions in the water. You train your nervous system instead of your aerobic system. Furthermore, you cn improve your SL at any age because it is skill-oriented, your ability to improve your SR is age-limited. Finally, the improvements that you make in your SL are permanent, you won't lose them even if you take a break from training. On the other hand, SR improvements depend on your fitness level. It makes sense that swimmers should invest more time in improving their SL and technique if they want to improve their swimming speed.

However, there is an optimum relationship between SR and SL if you want to achieve your maximum swimming speed. This relationship depends in the swimmers' size. Taller swimmers will typically use slower SR and cover more distance with each stroke than shortew swimmers do. More efficient swimmers use motions that generate more propulsive force with each stroke and reduce drag by taking more effective body positions and using more rhythmic movements and thus they will have a reduced SR. Swimmers with excellent kicks and swimmers with very large hands will propably also use slower SR and have greater SL. Finally, this relationship depends on the swimmind distance. You won't use the same SR and SL when you swim in a 100m race and a 400m race. The goal is not to achieve a single best count, but to learn the range of counts at which you can swim effectively

A few drills that will help improve your SL are:

•  SWOLF: This drill is so named because it involves swimming and is scores like golf. The value of the drill is that it allows each swimmer to discover the best way to improve the relationship between SR and SL to achieve a particular swimming velocity. The drill is performed in tha following manner. The athletes swim a particular repeat distance while counting their strokes. Their times are noted, and the two measures, number of strokes and their time for the swim, are combined for a score. Once they have established a base score, swimmers can use any one of several variations of the game to improve the relationship between SR and SL. The goal is to reduce the score by (a) swimming faster with fewer strokes, (b) swimming faster with little or no increase in the number of strokes taken, or (c) swimming the same time or nearly so with fewer strokes.
• Kick-ins: The kick-in drill works best for increasing SL. To perform it, athletes swim a series of 50 or 100 repeats while counting the number of stroke cycles required to complete each repeat. Before starting, each swimmer should be assigned the maximum number of cycles they are permitted to use for the repeat distance in the allotted time. That number should be one or two cycles fewer than they generally need to complete that distance. The goal, then, is to complete the repeats with fewer strokes. If they do not finish the repeat when they have completed their assigned number of stroke cycles, they must kick the remaining distance to the finish. The send-off time for the repeats should be set so it is challenging but manageable if the swimmers can complete the repeats without kicking in.     
• There are also a few drills where you swim at race speed and you try to reduce your stroke count from the beginning of the set to the end. A base score should be established on the first few repeats. You should try to swim the same time with fewer strokes or swim a faster time without increasing the number of strokes you take. The total distance of these sets should be short, only 150 to 300m, and the send-off time for each repeat should be long enough to allow you to swim at race speed without becoming fatigued.