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Between Limb Interference: How Smart is Your Right Foot?

  • 6/18/2014 11:28:00 AM
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Between Limb Interference: How Smart is Your Right Foot?

Deanna Kennedy, M.S.

It is well recognized that coordination is a fundamental aspect of skill related fitness. After all, many sports require some type of coordination between the limbs. Serving a tennis ball, for example, requires one limb to toss the ball while the other limb controls the timing and trajectory of the racket to facilitate contact with the ball. Swimming, on the other hand, requires a complicated pattern of coordination between the upper and lower limbs. While some coordination patterns are relatively easy for us to master, other coordination patterns have proved difficult or near impossible to perform. For example, try this coordination task, which was recently posted as a challenge on the web site: While sitting in a chair, lift your right foot off the floor and move your foot in a clockwise pattern. Then try writing a figure “6” with your right hand while you continue to circle your right foot in clockwise circles. Were you able to coordinate this complicated task? Were you able to get your right foot to continue producing clockwise circles? The answer to these questions is probably, no. Most likely, you ended up moving your foot and hand in the same directions. That is, you switched from producing a clockwise pattern with your right foot to making a counter-clockwise pattern so that both limbs were producing symmetric movements.

            The inability to simultaneously produce a clockwise circle with the right foot and a figure “6” with the right hand is well supported by research that has demonstrated that individuals tend to produce stable symmetric actions and that the performer often transitions from asymmetric actions(Kelso, 1995). That is, people tend to produce similar movements in both time and space with each limb. Furthermore, research has demonstrated that asymmetric coordination patterns (each limb producing a different movement in time and space) are less stable and more subject to spontaneous transitions to symmetric actions (Kelso, 1995). So, when you are trying to pat your head and rub your belly, for example, the right limb is supposed to be making a different movement from the left limb (asymmetric movement) but you end up either patting or rubbing both (symmetric movement).

            One possible explanation that appears to explain aspects of these coordination tendencies is neural crosstalk. Neural crosstalk is interference between the control signals for each limb. To coordinate asymmetric movements, the brain sends a control signal to each limb, but part of the signal is believed to be dispatched to the other limb resulting in interference. The interference is believed to push one limb (e.g., non-dominant) to produce the same movement. Currently, research is looking at factors such as attention and visual feedback manipulations to overcome these neuromuscular constraints to coordinating complex behaviors with the limbs. The hope is that one day we can quickly and effectively teach people to perform complex coordination patterns between the limbs and aid in rehabilitative protocols for stroke patients.

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