Children diagnosed with Developmental Coordination Disorder (DCD) (DSM IV; APA, 2000) exhibit motor issues that are due to factors other than known medical or cognitive condition, but are substantial enough to prevent them from meaningful participation in age-appropriate physical activities. This condition affects approximately 10 to 15 percent of school-age children, and it is more prevalent in boys as compared to girls (Crawford & Dewey, 2008). One of the most important characteristics of this population is its heterogeneity. For the clinical and research purposes children with DCD have been often classified based on their performance on formal assessment tests, such as Movement Assessment Battery for Children (MABC) (Henderson, Sugden, & Barnett, 2007). Those whose scores fall at or below 5%ile, in terms of normative data, are classified as having serious motor problems, whereas those whose performance places them between 10th and 15%ile are considered as having moderate movement problems. Regardless of the degree of their movement deficit, majority of them exhibit problems with many fundamental skills such as ball catching.
Background
It is known that typically developing children master one-handed catching around 10-11 years of age when 80% success rate emerges across a multitude of task demands such as different ball velocities and trajectories (Fischman, Moore, & Steele, 1992; Savelsbergh & van Santvoord, 1996). From the behavioral standpoint, mature one-handed catching is reflected in the tendency to contact the ball away from the body by actively extending the shoulder and elbow joints towards the ball (Savelsbergh & van Santvoord, 1996). This phase of one-handed catch is referred to as gross orientation or transport phase, and it precedes the orientation phase involving more refined adaptions of the wrist and hand leading to ball contact and catch. In terms of children with DCD due to limited research, the developmental trajectory for these individuals is unclear. Thus far only three studies examined this issue (Deconinck et al., 2006; Estil, Ingvaldsen, & Whiting, 2002), but only one used an ecologically valid catching task (Asmussen, Przysucha, & Zerpa, 2014). The study examined the nature of spatial and temporal coordination and control between 10 - 12 year old children with DCD, who exhibited serious movement problems (1-2% ile) and their typically developing peers. Functionally, children with DCD caught fewer balls, and exhibited a large degree of variability in the success rate (0% to 60%), despite the fact that all exhibited serious movement problems. In terms of coordination, both groups organized their actions in a similar manner at the proximal joints (shoulder-elbow), but not when the elbow-wrist relations were examined. Also, the differences between the groups were evident in both spatial (e.g., angular displacement of the wrist) as well as temporal aspects of control (e.g., linear velocity of the wrist).
It remains unclear why children with DCD fail to catch a ball, as from the motor control perspective a number of different perceptual and motor issues may contribute. Children with DCD exhibit deficits in temporal and spatial parameterization, especially when the movement preparation and execution requires a feedforward control strategy (e.g., Smits-Engelsman, Wilson, Westenberg, & Duysens, 2003). Also, a general motor planning deficit has been proposed as a possible information processing constraint (Schoemaker, Hijkema, & Kalverboer, 1994), resulting in less than optimal ability to scale force and time parameters of movement execution (e.g., Williams, Woollacott, & Ivry, 1992). As it stands, no research has examined how to change the status of these internal mechanisms in order for these children to place the hand in the right place, at the right time to intercept an oncoming object.