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Improving Goal-Directed Limb Movement: Don't Overthink This!

  • 7/18/2013 5:27:00 AM
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Improving Goal-Directed Limb Movement: Don't Overthink This!

Jason Boyle, Ph.D

Our nervous system is highly adaptable in perceiving, analyzing and executing movements in relation to an ever-changing perceptual environment. We use vision, knowledge of limb location, and anticipation of force production while simultaneously recognizing variability in our judgment to execute movements through the world around us. Whether it is simple (reaching for a door knob) or complex (threading a needle), goal directed movement has been repeatedly shown to follow a speed/accuracy tradeoff.


It has been shown that with aging, almost all human neural events become reduced in our cognitive and motor functioning. In goal-directed movement studies, elderly participants (65-95) compared to young (18-35) show decreases in a number of areas: overall movement time, smoothness, amount of corrections made, velocity and acceleration. The two groups do not however differ in movement accuracy, and interestingly elderly participants show increased brain activity when executing movements. This increased activity, however, seems to be more related to cognitive monitoring and effort than to functional control of activation. 


Recently, in a study investigating goal-directed limb movements, college-aged participants first practiced harmonic sine wave hand movements, then were given a test of rapid limb movement between two difficult targets (target widths = .05 o). The control group, which practiced the target task the entire time, did not have the sine wave practice and did not perform as well. These results are unique in that movements between equivalent targets have been repeatedly shown to follow a pattern of movement that is very slow, inaccurate and in-harmonic (i.e. not smooth) at any age. The authors conclude that the participants developed this enhanced form of performance not because they had learned the specifics of tracing the path but because the practice aided them in learning a new form of control to approach the targets. This strategy, to a degree, lessoned the “noise” on the nervous system and allowed them to smoothly and quickly move the limbs between the targets.   


Advancing this research to an aging paradigm, a recent pilot study has shown that following an optimized path not only improves movement times in the elderly, it does not sacrifice accuracy or movement variability. In other words, the elderly participants are developing a strategy similar to that of college-aged participants. These findings are important because the improved performance happens after the removal of the training feedback (the sine wave template) when the participants are free to move at the pace they choose. It is important to note that the participants used in the pilot study were recruited specifically from an active community of senior citizens who exercised at least three days a week in a local fitness club. It is highly likely that their active lifestyle of health and wellness played a role in their ability to adapt to the task demands and improve so significantly. These findings point out that exercise is an effective preventative measure to slow and even improve the natural declines associated with aging.


Finally, these findings transfer better if the sine wave is designed to promote an optimized path of performance, i.e., a sine wave that requires fast and accurate motion of the limb transfers well to a self-paced target task. In other words, just tracing or moving through a defined space is not enough. The movement has to be deliberate and through a motion that promotes optimized motor learning. These findings suggest that aging limb function can benefit from exercise, but maximally so from exercise that promotes these types of movements, for example yoga or tai chi.


Further Reading:

  1. Ketcham, C. J., Seidler, R. D., Van Gemmert, A. W., & Stelmach, G. E. (2002). Age-related kinematic differences as influenced by task difficulty, target size, and movement amplitude. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 57(1), 54-64.
  2. Boyle, J.B., Kennedy, D., & Shea, C.H. (2012). Optimizing the control of high ID single degree of freedom movements: Re-thinking the obvious. Experimental Brain Research, DOI 10.1007/s00221-012-3266-6.



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