The Importance of Inertia in Swimming Fast


The definition of inertia is the following: a body in motion wants to remain in motion, while a body at rest wants to remain at rest. It was first described by Galileo and later incorporated into the first of Newton’s three laws of motions. What does the law of inertia have to do with swimming? Lots.

Another way of looking at inertia is that it is far more efficient to keep a body moving at the same speed than it is to start it and stop it, or even slow it down, repeatedly. Because of inertia, we get better gas mileage on the freeway driving a constant speed of 70 mph than in town, averaging 35 mph, with lots of starts and stops.

As coaches, I think we often get hung up on the word ‘efficiency’. Efficiency is defined as the number of calories we burn to travel a certain distance in the water; in other words, it is our ‘gas mileage’ in the water. While that is important, efficiency per se does not win races. No one asks the winner of the Indianapolis 500 how the gas mileage was during the race. They don’t care. They just know that he or she got the checkered flag. The same goes with swimming. In order to be swimming fast and win races, we have to burn lots of calories. We simply cannot afford to waste them on unproductive motion.

In the sport of swimming, two of the four strokes conform more to the law of inertia than the other two. I call freestyle and backstroke the ‘freeway strokes’ and butterfly and breaststroke the ‘stop and go strokes’. It is partly due to inertia that the latter are either more difficult or slower than the former. Nonetheless, the law of inertia applies to all four strokes, as well as to starts and turns.

The reason that freestyle and backstroke conform more to the law of inertia than breast or fly is that there are more propulsive efforts occurring during each stroke cycle, particularly with a six-beat kick. In other words, there is less propulsive ‘down time’. The amount of propulsive ‘down time’ is important because as long as we are moving forward, frontal drag has no ‘down time’. That is, with our non-streamlined shape, frontal drag is working to slow us down at all times and quickly. Therefore, the only way we can keep a constant speed is by maintaining constant propulsion, which doesn’t happen with any stroke.

There are three ways to get on the freeway and maintain speed while swimming freestyle and backstroke; six beat kick, increased stroke rate and reducing frontal drag. At The Race Club, we focus on the importance of inertia and how each individual can try to best comply with our universe’s laws that rule us in the pool.

Yours in Swimming,

Gary Sr.

8 Responses to The Importance of Inertia in Swimming Fast

  1. Tom Zeller

    For Gary Sr.: Thanks for your tips. I’m an IU alum (and retired from an IU career) and took up swimming just a few years ago and now I’m hooked. I see Matt Mulligan most days at the IU pool (I think he was a frosh when you were a senior). Assuming you haven’t been to the IU pool in awhile, here’s a snapshot of the giant photo of you I swim below every day.

    Tom Zeller

  2. Tim Allen

    Coach Silvia (Springfield college) always taught inertia in his work. He had all kinds of sayings like the swimmer who is least muscular and more inertial swims faster farther. He also used Newtons third law of motion I believe to teach fly and breast. ACTION REACTION….Silvia and Counsilman were pioneers back in those days.You would enjoy his book….Silvia takes physics and shoulder joint limits and applies them to efficient stroke technique. Coach died in 96….all his films and work was recently discovered at the Hall of Fame…..somebody got it there, Buck Dawson or Sam Freas we suspect…..anyways, enjoy your Race Club Videos Gary….as a stroke tech myself, I love to analyze world class swimmers on your site. What a great knowledge you provide.

  3. Gary Hall Sr.

    Thank you Tom and Tim! Go I.U.! The wrinkles on the canvas in that photo in the Counsilman Natatorium have mysteriously shown up on my actual face.
    I recall Doc talking about Coach Silvia and the contributions he made to the sport of swimming. They were certainly an inspiration to all of us, particularly interested in the science of swimming fast.

  4. Pingback: The Peaks and Troughs of the Swimming Stroke Cycle - The Race Club | The Race Club

  5. Virginia Thompson

    Thanks for the wonderful information. I’m a novice at the age of 62. I look forward to becoming as good as I can at swimming. I enjoyed learning about the Importance of Inertia. I had no idea swimming involved so much.
    Do you know of a good swim snorkel that is silicone free? Apparently I’m allergic to silicone. I love the swim snorkel as I’m learning to roll. Something I never really did before. My coach Joe Biondi here in Florida is amazing. I can already swim up to 60 lengths and possibly more without getting exhausted after two lengths. However, the swim snorkel is keeping me from being able to swim as I got pretty sick from it. I have been searching the web to find a good snorkel but haven’t even been able to find one at all. Please help if you can. Sincerely.

    • Gary Hall Sr.

      Good for you, Virginia! I am not aware of a snorkel that doesn’t use a silicone mouth piece…which is the source of the problem. There are quite a few good snorkels on the market, but I am partial to the DMC snorkel which is smaller and more comfortable than some of the larger ones. It doesn’t create such a drag when pushing off of the walls.

  6. Mark Buchanan

    Hi Gary and coaching staff I recently watched a short video on how to use lane lines to work on setting up the approach to turns by gliding just underneath them. During the description of how to do the drill the coach mentioned a term i had never heard of “double cutting the water” Do you by chance know what he means by this. I would like to take this to my swimmers but not until i know what this means. Any help would be appreciated. I love your articles in aqua notes by the way. Cheers mark Buchanan

  7. Gary Hall Sr.

    That is a new term for me, too, Mark. If you find out, please let me know.


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