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What does the index of coordination (IdC) have to do with swimming faster?

The IdC is a measure of arm coordination in freestyle. Specifically, the IdC indicates if the arm coordination is less effective by producing gaps in propulsion or if the arm coordination is more effective by producing a more consistent source of propulsion. The main benefit of more continuous propulsion is faster swimming.

An effective freestyle with “no gaps in propulsion” has been supported by research since at least 1955 (Counsilman). Since then, numerous other studies concluded that gaps in propulsion were counterproductive and should, in fact, be considered a technique error (e.g., Chollet, Millet, Lerda, Hue, & Chatard, 2003; Schnitzler, Ernwein, Seifert, & Chollet, 2006; Seifert, Boulesteix, & Chollet, 2003).

The IdC was developed in 2000 to quantify the relative position of the arms throughout the stroke cycle, (Chollet, Chalies, & Chatard). A zero IdC occurs when one hand begins to pull at the same time that the opposite hand completes the push (middle image). With a zero IdC, the arms are in opposition throughout the stroke cycle.

Index of Arm Coordination

A negative IdC occurs when the entry arm does not begin to pull when the opposite arm completes the push (top image). The failure of the entry arm to begin to pull causes gaps in propulsion. A negative IdC is also called catch-up stroke.

A positive IdC occurs when the entry arm begins to pull before the opposite arm completes the push (bottom image). A positive IdC is also called superposition, as there is an overlap in arm propulsion for a more continuous source of propulsion.

The science overwhelming supports a positive IdC for the fastest swimming. Yet, swimmers are almost always using a negative IdC, often -5% to -10% and even lower. A swimmer cannot maximize velocity with a negative IdC.

Swimmers usually only use a positive IdC at velocities above 1.8 m/sec. Even at the fastest swimming velocities (over 2.0 m/sec), an IdC above 5% is rare. An IdC over 10% and probably over 20%, however, is possible and also essential for the fastest human swimming.

Unfortunately, typical training promotes a negative IdC. Swimming longer distances at a slower stroke rate, fatigue, and an arm entry parallel to the water surface all encourage a delay in beginning propulsion with the entry arm. The result is that swimmers are usually practicing an arm coordination that is counterproductive to swimming fast.

Fortunately, there are strategies that can help a swimmer learn to swim with a positive IdC and make use of the arm coordination that produces the fastest swimming. Optimizing the IdC requires 1.) mastering an effective downward angle on the arm entry, 2.) maintaining primarily backward hand motion as the torso rotates upward on the push phase, and 3.) gradually increasing the speed of the arm recovery with an increasing stroke rate. Any swimmers who hope to optimize performance would do well to evaluate their own IdC and work to improve it.


Interested in IdC? Follow the links below to learn more!

https://www.youtube.com/watch?v=DYn51lJxO6U

https://www.iat.uni-leipzig.de/datenbanken/iks/bms/Record/4019193

https://www.iat.uni-leipzig.de/datenbanken/iks/bms/Record/4032674

By | September 23rd, 2019|blog|0 Comments

Can Less Mean More?

How Triathletes Can Get the Most Out of Limited Time in the Water

We get it: There is a limited amount of time that a triathlete can spend training in any one sport. It doesn’t help that swimming is most likely not a triathlete’s favorite event – or that access to water for training might be a significant impediment to training year-round.  So how can you make your swimming more effective and improve your finish times – without increasing swim training times?

For starters, science doesn’t push for ever more time/distance in the water as the best way to improve your swim times. In fact, just the opposite is true: research suggests that even a limited time in the water can produce a substantial improvement in performance time. Obviously, no one is advocating that swim training isn’t required to be successful. Instead, this post – and the significant research behind it – suggests 5 ways you can make the most out of every swim.

  1. Dedicate a large portion of your time in the water to swimming slow. This allows you to avoid fatigue and focus more on technique.  Your goal is to establish a regular routine of short, slow swims with the priority on skill improvement.  (Your endurance training with your biking and running make this focus on technique swimming possible.)
  2. Practice breathing less frequently to improve visual input. When swimming slower, a swimmer can minimize the number of breathing strokes. If the head is motionless on nonbreathing strokes, swimmers can better focus on visual input. They will be more certain of what they see and be better able to control their movements using visual feedback. This will also help when you are swimming in open water when conditions are less than ideal.
  3. Set a goal and work towards improving technique on every swim. Strokes performed with an ineffective technique (because of fatigue, speed, breathing, etc.), are not likely to improve or reinforce effective technique. It is essential to practice your technique to develop skills that enable you to swim faster. It’s far better to swim more slowly while focusing on technique elements like arm entry, head position, pulling through to the thigh on each stroke, etc., than it is to swim as fast as possible for as long as possible.
  4. When possible, practice in race-specific conditions. The ultimate goal of skill-learning is to maintain the most effective technique throughout an entire race. A reduced distance regimen allows more time for swimmers to practice under simulated race conditions (i.e. choppy water, swells, transitions). For example, training sets that include a start from shore provide swimmers with the opportunity to practice starts.
  5. Get feedback from a coach or fellow triathlete. While many triathletes work regularly with both sport and strength coaches, many do not. For both, asking for feedback on some aspect of your swimming technique can provide valuable information. For example: Is your head level when not breathing? Do you raise your elbows the same way on left/right hand strokes? Are you “dragging” your legs or is your body position basically level? Are you rolling your body excessively when you begin your stroke? This kind of feedback is essential to improving technique. If you are fortunate enough to have a swim coach, don’t be shy about asking for a regular short technique assessment. Getting a friend to video record your stroke for you to see can also be an eyeopener.

The bottom line: A limited amount of time spent swimming results in fewer stroke cycles and allows a triathlete to focus on technique in a way that enables lasting change.  Fewer cycles also mean less shoulder stress and pain. Shoulders that are not stressed and not suffering from inflammation are not as likely to interfere with swimming, biking or running. Which means: you can get the most out of your practice swims, swim faster with better technique, and devote more time to the rest of your packed schedule.

By | June 21st, 2019|blog|0 Comments