There are several bits of teaching advice that hold true for all strokes, such as keeping your face and head in the water as much as possible. The head is at one end of a seesaw that is the body, which pivots around the center of buoyancy, located roughly in the lower chest.

The legs are at the other end of the seesaw, and they help to keep the seesaw level by kicking. They go up and down. The knees go up and down. The shoulders go up and down, either together or rotated side-to-side. And so does the head.

What, then, if anything, stays steady?

Keeping your hips on the surface is the key to efficient stroking. If the hips drop, the body’s front creates huge resistance to forward motion. This is true for all strokes.

It would seem intuitive for the front and back crawls and possibly even for the breaststroke. But the butterfly?

Actually, I have analyzed the “fly” of an Olympic champion against a grid background for a graduate school paper. The head, shoulders, knees, and even the center of gravity made a wavelike pattern through the stroke. The latter determination was particularly tough in the days before computers.

But the hips maintained a steady line through the stroke, and my observations since then of top butterflyers have confirmed this. So all the strokes are swum better when the hips remain at the water surface.

Knowing this, how can you perform your strokes to keep your hips where you want them to be? For front crawl, you need to keep a steady kick, not a hard or fast kick, with relaxed legs from the hips down. The goal is not increased propulsion, but reduced resistance. This is easier to do if your face is in the water.

Obviously, the same holds true for swimming on your back, just an easy kick with head back up to your goggles. For breaststroke, keep the hips at the surface by keeping your face under water after taking your breath and during your kick. And for butterfly, feel your hips rise behind you with your head underwater after stroking and breathing.

The purpose of keeping your hips at the surface is to enable you to extend your glide position as long as possible so that you take fewer strokes each pool length, which is the best self-measure of stroke efficiency.

Dr. Bob Colyer of Bluffton is an actively retired college professor, coach and author of “Swim Better: A Guide to Greater Efficiency for Swimmers & Instructors,” directed primarily to non-competitors.