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A Kinematic Comparison of Dive Fins

Discussion in 'Force Fin' started by Blair Mott, Jul 22, 2008.

  1. Blair Mott

    Blair Mott Dive Equipment Manufacturer

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    Recently, I had a chance meet and talk with Ryan Lindsey, a master of kinetics and biomechanics.


    [​IMG]
    Ryan Lindsey, his daughter Charisse and Bob Evans all with their new favorite Force Fin.

    In 1996, Ryan finished his Academic Masters at San Diego State University in this discipline. He has been working in the field ever since, but it is his work and the results of his Master’s Thesis Kinematic Comparison of Swimming With Two Different Dive Fin Designs
    that I would like to share with the ScubaBoard members and guests today.

    There are fin studies out there that use air consumption, thrust and distance as units of measure to determine how a particular fin compares with other fins. These studies have their limitation since it is difficult to get a large enough sample and control for the individual subjects’ predispositions, with respect to fin use and overall physical condition. Ryan Lindsey’s Thesis is different. It uses a tool of analysis that quantifies fin use and really gets to the guts of a fundamental reason as to why Force Fins are different and how those differences make Force Fins better.

    The purpose of his study was to determine the difference, if any, in the mechanics of legs only swimming while utilizing two different designs of dive fins. The two designs were conventional fins and Force Fins.

    Conventional fins utilize a flat blade shaped surface to provide propulsion, as well as an enclosed toe foot hold. Force Fin® incorporates a blade surface that is shaped like a whale tail, with a patented up-curved shape and open toe foot hold that rests across the instep of the foot. The toes are free to move independent of the Force Fin blade. It is these two differences that dictates the way the human leg responds as it moves the fin blade through the water.

    Ryan told me, “The body is a perfect machine, but it has design limitations.” The leg can bend, lift and push in many different positions, but the joints are designed to lock when moving forward and bend when pulling back.

    Ryan used a biomechanical analysis software program called Peak5® to digitize video footage of a swimmer moving past a viewing window in a pool kicking conventional fins and when kicking Force Fins. The software translated the range of motion, acceleration and velocity the hip, knee and ankle joints into data points that show the differences in that range of motion to reveal the strain put on those joints of the leg when kicking the fins.

    Ryan was getting real information on the different effects of using different fin designs in the water, a comparison with no room for human interpretation. With the Peak5® software he could translate video footage of a diver’s leg in motion into percentages of range of motions on joints of the body, interpret forces acting on legs using known bio-mechanic norms and limitations of the human leg.

    When I read this I immediately looked up on the wall in the Force Fin® office and saw Bob Evans’ famous painting he did in 1971 of a leg “kicking motion”. This painting is the first thing Bob Evans, inventor of the Force Fin® did when he decided he wanted to make a better pair of dive fins. The drawing shows a human leg going through the range of kicking motion. I took the it off the wall and had Ryan explain a few things to me.
    [​IMG]

    Ryan Lindsey points to a point where normal ankle range of motion stops in a kick cycle.Bob Evans famous painting he did in 1971 of " The Motion of Kicking". First thing he did when he knew he wanted to make better diving fins was to create this painting.


    Ryan explained to me that if a fin forces an ankle beyond its normal range of motion, it causes intense ballistic strain on the front of the lower leg. When you enclose the toes in a foot pocket and push a flat shape fin blade through the water the foot is forced into extreme plantar flexion. This over contraction on the muscles results in micro trauma, which causes muscle spasms that induce cramps over time. In his study the Peak5® software showed the ankle of the diver using conventional fins was forced beyond its normal 90 to 180 degree range of motion.

    In contrast, when wearing Force Fins the toes are exposed. This is why when using Force Fins your ankle never goes past the normal range of motion and you will not experience the intense ballistic strain caused when wearing conventional fins. It is also one reason you do not feel the power of Force Fins.

    [​IMG]

    Force Fins open out during the downward stroke to maximize the surface area pushing against the water. The shape of the Force Fin and its high quality material snaps back to its original shape on the up stoke allowing the diver to use less energy to create forward propulsion. This allows isolation of power output from the quadriceps, and limits strain on all other weaker muscles and the joints of the leg.

    I have used Force Fins for over decade, and talking to Ryan Lindsay was a true honor and very inspiring. He took the time to explain his work and I hope I have interpreted his study for you to have a better understanding of the kinetics and biomechanical differences of using two different types of fin designs. Ryan told me, “using fins underwater traditionally uses a lot of hip, knee and ankle and it hurts! ….. Why does it have to hurt?” Those who don’t like Force Fins might because they can not feel them. Hopefully, this will help some of them understand why, so that they too can free themselves from unnecessary strain!
    It really is a Smart Fin![FONT=&quot]
    [/FONT]
     
    Last edited: Jul 22, 2008
  2. uncleavi

    uncleavi Instructor, Scuba

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    Another great post!
    I consider myself a lay level Force Fin fanatic and do love reading about this stuff.
    Now a bit wiser, I just finished rinsing off my SD-1 Military Fins and did yet another backyard dive. Now to make Dinner.
     
  3. meesier42

    meesier42 Divemaster

    # of Dives: 500 - 999
    Location: Kennewick, WA
    1,267
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    wow, I LOVE IT. thanks for the insight, I love learning something new, especially when it proves that we have been right all along.

    Can I get a copy of the entire thesis paper??
     
  4. Souvy

    Souvy Angel Fish

    # of Dives: 50 - 99
    Location: Boston, MA
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    Great post, thanks Blair!
     
  5. Blair Mott

    Blair Mott Dive Equipment Manufacturer

    881
    16
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  6. Bob Evans

    Bob Evans Manta Ray

    # of Dives: I'm a Fish!
    Location: Santa Barbara, California USA
    1,151
    205
    63
    I must be living in the dark ages. You would think our diving agencie's or insurance companie's would perk up with this post. Fin design that eliminates the number one cause of cramping vs. fins that cause cramps by design. The achilles heel of other fins. Come on this is a better issue than a fin's price.
     
  7. Bob Evans

    Bob Evans Manta Ray

    # of Dives: I'm a Fish!
    Location: Santa Barbara, California USA
    1,151
    205
    63
    No it is not a sad day for Force fins, its a sad day for divers who get leg cramps.
     
  8. meesier42

    meesier42 Divemaster

    # of Dives: 500 - 999
    Location: Kennewick, WA
    1,267
    65
    48
    sad day for ForceFins! , to me it sounds like a good day for ForceFins and those "others" that get leg cramps. As it is today that they finally have academically reviewed evidence that they can eliminate the cramps forever just by changing their fins
     
  9. dumpsterDiver

    dumpsterDiver Instructor, Scuba

    # of Dives: 2,500 - 4,999
    Location:
    8,319
    4,017
    113
    So force fins are good for people that get leg cramps? what about the rest of us?
     
  10. meesier42

    meesier42 Divemaster

    # of Dives: 500 - 999
    Location: Kennewick, WA
    1,267
    65
    48

    as you have seen in the first couple of post, this study was about the mechanics of fin swimming not thrust or power. In the study of the mechanics (or biomechanics as it is) it has shown why convential fins have a higher incidence of cramping and ForceFins act to limit the cramp causing muscle damage. From this an intelligent person would also note that by reducing muscle damage they would also increase their muscle performance under load allowing them to maintain peak performance longer. So when you have to go fast, you can do it longer, while going faster, with less pain. When you don't have to go fast you are more comfortable.
     
    Last edited: Aug 3, 2008

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