Unlocking the Secrets to Faster Swimming: Insights from Jan Prins' Biomechanical Research

Unlocking the Secrets to Faster Swimming: Insights from Jan Prins’ Biomechanical Research

Swimmers looking to improve their freestyle stroke mechanics will find valuable insights in Jan Prins’ updated paper. Prins, a renowned expert in swimming science, delves into the biomechanics of swimming strokes, emphasizing the importance of impulse and asymmetry in generating propulsion. Through his 16-part program, “Freestyle Biomechanics – The Science Behind the Strokes™,” Prins provides a comprehensive guide for swimmers of all abilities, sharing techniques for swimming more efficiently and effectively. In this blog post, Dr. Prins shares his research which highlights his key insights for swimming faster and smarter.

The Biomechanics of Unintended Consequences

Part I

Jan Prins, Ph.D.
Aquatic Research Laboratory, University of Hawaii
Swimming Biomechanics Inc.

The paper “The Biomechanics of Unintended Consequences” was first published in 2009. [1] The impetus for this Update is because we can now examine select areas related to stroke mechanics in more depth, using high-speed videography and motion capture software.

This paper will be divided in to two parts.  In Part I, following an overview of the methods we use to video tape and analyze swimmers in biomechanical research, we will focus on the following areas of interest. (1) Impulse – the ability to apply a force over a period of time – as applied to swimming; (2) Asymmetry – How dissimilar motions between the Left and the Right arm pulls affect overall propulsion.  We continue in Part II discussing (1) The “S-Pull” – Why this is no longer advocated; and (2) the Conscious Repositioning of the Scapula. 

The Freestyle is used as the primary stroke for these discussions.

A video-based version of these topics is available Freestyle Biomechanics – The Science Behind the Strokes™.

High Speed Videography & Motion Analysis in Swimming

The technology used is the result of more than 20 years of research and developmentWe use three synchronized high-speed cameras.  The Frontal View allows us to check essential points such as Hand Entry, Elbow Bend, and the Paths of the Hands.  The Vertical View, where the camera is set directly below the swimmer,allows us to monitor Body Line and Amplitudes of the Arm Pull.  The Lateral View is the most important, because it allows tracking of the swimmer’s Hip Velocities.

Figure 1:  Underwater Videography – We see 2 of the 3 synchronized cameras:  the Frontal camera and the Vertical camera (pointing straight-up to the surface from the bottom of the pool).

After filming, motion analysis software is used to study the swimmer’s stroke.  We track the movement of the hip in the longitudinal plane of motion.  The software generates a Report, matching the three synchronized videos with a graph.  The vertical bar in the graph tracks the light on the swimmer’s hip and shows the swimmer’s velocity (Figure 2).

Figure 2:  Freeze frame of video-based “Report.”  The software allows simultaneous viewing of the synchronized videos with an active graph.


Focus 1: Impulse as applied to swimming

Impulse is the ability to apply a force over a period of time.

In swimming, it is not necessary to exert the highest possible forces during the underwater pull.  Instead, we must try to exert sufficient force to maintain peak swimming velocities over a longer period of time during each stroke cycle.

Typically, swimmers will try to accelerate the hands during the last third of the underwater pull.  Using motion capture technology, we can track the changes in hip velocity in response to these rapid changes in hand speed.  

Figure 3:  Report displaying freeze-frame of left hand in the underwater pull. The vertical bar in the graph is paused at the “push-phase.”  Peak hip velocity was maintained for approximately 16% of total underwater pull.

As expected, in this example we see a surge in this swimmer’s velocity occurring as the left hand is completing the “push phase.”  We can also see that this period of peak hip velocity is brief. 

The approximated durations of peak velocity, when the body is moving at its fastest, is sustained only briefly.  In this example, for only about 16% of the total period of the underwater pull for the left arm.

The question is … Can we do better?

The answer is Yes—increasing Impulse means reaching a higher swimming velocity earlier in the stroke, and trying to maintain it until the completion of the underwater pull in the “push phase.” 

Here’s a Report of a swimmer doing better with maintaining peak velocities for longer periods of the underwater pull—we see flatter portions of the velocity curve.

Figure 4:  Report showing more sustained periods of peak velocities exerted by both arms.

The final example demonstrates what a elite swimmer is capable of in terms of the ability to reach peak hip velocities early—starting a little after the Catch—and sustaining it for a good portion of the of the underwater pull.  Peak velocity in this example was held for approximately 58% of the total duration of the pull.

Figure 5:  Peak hip velocity maintained for approximately 58% of total underwater pull.

The swimmer in this example is James Magnussen, two-time World Champion in the 100m Freestyle, and Olympic Silver Medalist in the same event.

In conclusion, we need to remind ourselves that we increase impulse in swimming by ensuring that the “Catch” begins with a firm hold on the water, with the intent of maintaining this pressure as the pull progresses.  It is just as important to not wait until the final phase of the stroke to dramatically increase hand speed, expecting that this late application of force will maximize overall swimming speed.


Focus 2:  Asymmetry in the Freestyle

When focusing on symmetry in swimming, the general expectation, what we would like to see, is that both sides of the body perform similar pull patterns and exert similar propulsive forces.  Unfortunately, we know that when it comes to human motion, regardless of the level of ability, this is not possible.  We will always have some degree of asymmetry in all four competitive strokes: Unilateral arm motions (Freestyle and Backstroke) and Bilateral arm motions (Breaststroke and Butterfly).  This is easily seen when viewing the frontal view, of the swimmer swimming directly towards the camera.  

Two excellent papers are available on Swimming Symmetry by Dr. Ross Sanders, published in the ASCA Journal of Swimming Research:

  • How Can Asymmetries in Swimming be Identified and Measured?  Ross H. Sanders, et al. Journal of Swimming Research: Volume 19:1 (2012)
  • How Do Asymmetries Affect Swimming Performance?  Ross H. Sanders, et al. Journal of Swimming Research: Volume 21:1 (2013)

It’s safe to say that most swimmers, after swimming regularly for some time, can detect—either intuitively, or following an underwater video analysis—that asymmetry does exist in their pull patterns and both hands are not performing uniformly.  The important question is how much do these variances actually affect swimming speeds? 

Presented here is an excellent example of how much asymmetry does affect performance.  We had the opportunity to analyze Michael Weiss, a world-ranked Freestyler (U.S. National Team member, World University Games Record Holder, and World Championships Relay medalist).

Having been video-taped and tested extensively, Michael was aware that his left hand, was performing more efficiently, but was unclear of just how much. The ensuing results turned out to be useful, insofar as we were able to quantify the difference in pulling efficiency between each arm.

Shown here are the two freeze-frames of the peak velocities generated by the two pulls.  As anticipated, we see a difference, and what is revealing is the degree of variance.  The calculated difference in peak hip velocities was a significant 19%.

Figure 6:  Peak hip velocity generated by the right arm pull.

Figure 7:  Peak hip velocity generated by the left arm pull.

Michael addressed this imbalance by increasing his awareness of the changing pressures of the water on his palms, especially on his right side.


Jan Prins

Director – Aquatic Research Laboratory, University of Hawaii
Freestyle Biomechanics – The Science Behind the Strokes™

[1] The Biomechanics of Unintended ConsequencesJan Prins, American Swimmer: Vol 2 (2009)

Courses and Webinar on WOWSA

Freestyle Biomechanics is designed to assist Coaches, Teachers, and all Freestylers, with special tips for Triathletes and Open Water Swimmers. The 16-Section program covers all aspects of the Freestyle Stroke in detail.

Video recording of the Improve Your Freestyle – Swim Faster and Smarter – Freestyle Biomechanics Webinar!

Freestyle Biomechanics covers the freestyle stroke from all angles and shows the most efficient techniques for swimming fast and safely – highlighting exactly what you want to do and what you want to avoid!

Jan Prins, Ph.D

Jan Prins is currently a member of the Faculty at the University of Hawaii where he directs the Aquatic Research Laboratory and teaches Sports Biomechanics.

He has been involved with swimming for over 40 years.  His primary focus is assisting Competitive & Masters Swimmers, and Triathletes with improving their swimming stroke mechanics.


  • For the past 22 years, he has been involved with unique swimming research, analyzing the stroke mechanics of elite swimmers, including Olympic Gold Medalists, FINA World Swimming Champions, and former World Record Holders.
  • He has presented his research at national and international swimming conferences, including the ASCA World Swim Coaches’ Clinics.
  • He was the Editor-in-Chief of the Journal of Swimming Research and the recipient of the American Swimming Coaches Association “Bob Ousley” Award for contributions to the sport.


  • He has conducted Video Workshops for Competitive & Masters Swimmers, and Triathletes for over 35 years — filming and analyzing above- and underwater stroke mechanics.
  • He was the Head Assistant Coach under the legendary “Doc Counsilman” at Indiana University, where he received his Ph.D. in Human Performance.
  • He served as Head Men’s Swimming Coach at the University of Hawaii. During his tenure his teams placed in the “top 20” at the NCAA “Division I” Championships, and in the “top 10” at the USS Senior Indoor Championships.
  • He was the coach for Sri Lanka in the 1984 Olympics in Los Angeles and the 1986 Asian Games in Seoul.
  • He was a member of the United States Paralympic Swimming coaching staff at the 1992 Paralympic Games and the 1994 World Paralympic Games.
  • He worked with the United States Armed Services Wounded Warrior Program and was a member of the coaching staff of the United States Team at the inaugural “Invictus Games” held in London, U.K. (2014).


“What Jan Prins has developed in Freestyle Biomechanics is a step beyond what anyone has done before. It is an excellent teaching tool that I can use in coaching my Masters swimmers and Triathletes, especially those beginners eager to improve. The underwater video quality is superb.
Jan breaks down the Freestyle stroke into the most concise format possible.”

~ Jim Montgomery Coach – Master’s and Triathlon Swimming. Olympic Gold Medalist & Former World Record Holder. First swimmer to break 50 seconds in the 100-meter Freestyle.

“Dr. Jan Prins has developed a series of instructional videos for the Freestyle that are “state of the art.” The photography is exceptional, showing underwater and above-water views of swimmers from a wide range of skill levels. His descriptions of the strokes are delivered concisely and accurately in understandable language that is always supported by video that clearly demonstrates the point he is making.

The Freestyle Biomechanics videos also include a section on common mistakes. The knowledge gained during his many years of coaching and teaching swimming are definitely on display here. The swimmers making these mistakes are not swimming “wrong” for the camera. They are actual Club, Masters, and Triathlon swimmers who are the embodiment of those in your pool who are making the same mistakes. Thus, making it easier for the coach and teacher to spot those mistakes and correct them. I can promise you, that this set of videos will be an invaluable aid to any Coach or Teacher of swimming who uses them.”

~ Ernie Maglischo, Ph.D. Internationally recognized authority on swimming stroke mechanics. Author of the “Swimming Faster” textbook series.