One of my regular readers told me she had a problem. It was hard, she said, to keep her thumb close to her other fingers while she was swimming.

I told her I had good news; she didn’t have to do that.

Fifty years ago, Dr. James Counsilman, my mentor, published “The Science of Swimming,” still the bible of the sport – especially its 25th-year revised 1994 edition. Doc (as he was known to all) was the most accomplished aquatics teacher and coach in the world, with an insatiable curiosity about all aspects of swimming.

In his first chapter, Doc wrote about his experiment in a wind tunnel with plaster molds of hand shapes – open, closed and cupped. He wanted to see locomotion.

A relaxed and effective stroke is a worthy goal for any swimmer, recreational or competitive. Maintaining an open hand position, always below a high elbow, can make a big difference in achieving efficient swim strokes.

Getting the most out of each stroke and taking fewer strokes per length makes swimming easier, more relaxed, and comfortable. Be curious and experiment which shape creates the most resistance, which would make it most effective in propulsion against the water.

The cupped hand created the least resistance, using less surface area and a less hydrodynamic shape. The others were essentially equal, having the same surface area, whether the hand was held with fingers and thumb together, with fingers and thumb spread as far apart as possible, or with the fingers and thumb held somewhere between those two extremes.

Because they function equally, is there any reason to prefer one of these three hand positions? Indeed there is.

In order to keep the fingers and thumb close together or far apart, there needs to be tension in the swimmer’s forearm, wrist and fingers. Such a strain will produce fatigue in the hand, especially when swimming longer distances, thus reducing propulsive force over time.

On the other hand (pun intended), if the swimmer keeps a more comfortable open hand, between those extremes, without any strain, there will be less fatigue. Propulsive endurance is increased.

Not only that, but a relaxed hand throughout the stroke, especially during recovery (just dangle the fingers), works toward my goal in these columns – efficiency of aquatic propulsion for yourself. You’ll be happy with the results.

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.