Swim efficiency

Choosing a swim style and distance is very personal, it depends on many psychological and physiological factors. For example, everyone does not feel the need to cross the Channel in swimming...

Depending on the distance practiced, one of the three energy sources: alactic anaerobic(A), lactic anaerobic(B), aerobic(C), becomes dominant and requires a specific technique (Ref.).

Swim styles

The most common swim styles are the following:
• Front crawl stroke : it's the faster swim
• Butterfly stroke : it's the most technical swim
• Back crawl stroke : it's the less technical swim
• Breast stroke : it's the slower swim

The comparison of mean speeds for the world records, give a good overview of the possibilities of each stroke.

Men (pool of 50m)
Distance (m)	Mean speed (km/h)				Source
	Crawl	Butterfly	Back	Breast
50	8.57	7.83	7.50	6.67	A
100	7.66	7.20	6.92	6.21	A+B
200	7.06	6.49	6.43	5.67	B
400	6.55	-	-	-	B+C
800	6.37	-	-	-	C
1500	6.20	-	-	-	C

Women (pool of 50m)
Distance (m)	Mean speeds (km/h)				Source
	Crawl	Butterfly	Back	Breast
50	7.50	7.20	6.67	6.21	A
100	6.92	6.43	6.21	5.63	A+B
200	6.37	5.90	5.81	5.18	B
400	6.03	-	-	-	B+C
800	5.83	-	-	-	C
1500	5.77	-	-	-	C

Fluid dynamics

Water is a viscous fluid which requires an excellent technique to minimize the friction.

The swimmers have very different morphologies depending on each stroke (breast, butterfly, freestyle, etc.) as well as the distance (a short-distance swimmer does not look like to a long-distance one).

Even if this situation is common to other sports (running, cycling, etc.), in swimming it takes a huge importance. A swimmer should adapt his technique to his morphology and will be able to compensate in glide his lack of power.

The two main dynamics phenomena to consider for a movement in the water are the viscous resistance and the front wave resistance.

The viscous resistance is the most important phenomenon. It depends on the water viscosity which generates a friction. The "pull-push" chains allow decreasing this resistance from a perfect synchronism.

The front wave resistance is a phenomenon coming from the head and the shoulders as for a boat stem which generates a wave which opposes to the movement. The position of the body is fundamental to limit this resistance.

Swimming techniques

For aerobic crawl, the swim style of Sun Yang during his 1500m world record, is very revealing. Note the energy savings achieved with the legs for 6.20km/h of mean speed...

For butterfly stroke, the swim style of Michael Phelps is also very interesting.

J.L