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• 1 2019-10-13T15:05:21-07:00 Dysfunctional anticipatory and feedback responses 31 plain 2019-11-28T17:33:35-08:00 Effective postural stability requires both sensory organization and motor response organization (Nashner et al., 1989). Grove et al. (2007) examined the sensory organization of postural stability in DCD children by analyzing their ability to rely on changing degrees of somatosensory, visual and vestibular feedback, as seen in the motor control loop.DCD children demonstrated impaired static balance under conditions where vestibular feedback was the only accurate source of orienting feedback, as seen in the graph below (Grove et al., 2007). Moreover, half of the children with DCD displayed static postural instability that was greater during inaccurate visual feedback conditions, in comparison to conditions where visual feedback was reduced (Grove et al., 2007). Geuze et al. in 2003 and 2005 also found that DCD children had trouble with static balance only in challenging or new situations, specifically when they needed to rely on the vestibular system.
  
  
  
  In contrast, feedforward mechanisms such as automatic postural responses (APAs) help maintain postural stability by preventing the perturbation of the center of mass (COM) (Johnston et al., 2002). Johnston et al. (2002) investigated the timing of muscle activity and resultant arm movement during rapid voluntary goal-directed movement. It was observed that the onset of activation of all trunk muscles occurred during the APA period in TD children (Johnston et al., 2002). However, DCD children showed activation of only two out of five trunk muscles at the onset of the APA. To date, most studies on postural muscle functions have focused on maintenance of stability following an external perturbation (Johnston et al., 2002). This study was significant as there is little information on postural muscle function in DCD children. This coincides with Geuze’s (2005) findings, which states that DCD children show inconsistent timing of muscle activation sequences, lack of automation and slowness of response.