Friday, 28 October 2011

Children throwing bean bags at targets

Yesterday I spent a couple of hours in the Biomechanics lab here at the Centre for Sport & Exercise Sciences. The lab is fully instrumented, with 10 cameras mounted 360° around the room integrated with a force plate built into the floor. This arrangement allows us to place passive markers (small pieces of reflective plastic) on a person and track these within quite a large volume of space; if one camera loses sight of the marker, one of the others can typically see it. The data from the cameras and force platform come out with a common time stamp, so you can line the data up and see what was happening when.

The reason I was in the lab was to try out a bright idea I've had with a colleague from Leeds Metropolitan for a study. One of the tasks I use to study perception and action is throwing over long distances to hit a target. I ask people to throw overarm to hit a 4ft x 4ft Perspex target from up to 15m away, and we record their throw with high speed cameras to measure the release angle and velocity of the ball. I'm also interested in the development of throwing; this is a very human skill, with all kinds of interesting psychological properties. It's considered a key motor skill for young children to acquire, so much so that it is one of the tasks measured in the Movement Assessment Battery for Children (Movement-ABC). This battery is commonly used to identify children with motor difficulties such as developmental coordination disorder, and throwing is one of the assessment tasks.

In the Movement-ABC, the child is asked to stand with their feet together, look at a target on the floor 1.8m away, and throw a bean bag to hit the target. The assessment battery is designed to be used with a minimum of equipment and fuss, so the outcome measures are simply how often the child hits the target; this score is then related to the battery's published norms. 

To study something as complex as throwing, you have to constrain the task without compromising how iinteresting it is. In order to secure funding to study throwing, I need to be able to show there's a reason other than 'I am very interested in this topic'. The bright idea we've had is to study throwing in children, using the Movement ABC task as the core task. We will then be able to a) take detailed kinematic measurements from the children, including the motion of the beanbag, the coordination and timing between the limbs, and how this relates to the ongoing control of posture, and then b) relate everything we find to performance in a commonly used clinical assessment measure. 

My colleague, Dr Charikleia Sinani, brought in two of her friends and three children aged 3, 4 and 8. We had them stand on the forceplate and placed markers on key points on their upper bodies (shoulders, down both arms, and hips). We then asked them to make a bunch of throws to the target while we recorded them. I wanted to convince myself we could, indeed, measure what we wanted from young children, who are typically enthusiastic but not especially reliable participants in experiments like this! We recorded a lot of data and I'll blog some of what we found as I work my way through it; but for now, I'm happy that we we'll be able to get the kind of data we need. It will be tricky (keeping markers in stable positions on fidgety children is tricky, and getting them into a nice rhythm of throwing when we're recording is a lot harder than with adults) but, importantly, doable.

Why is this interesting? As I said, throwing is a key skill for children to learn, and children with problems such as DCD (or even milder, less specific issues) find this complex task very challenging. This has all kinds of knock-on effects - these children are less likely to play sports requiring throwing, and so are less fit and healthy, plus there is a social cost to not participating in these games. The DCD research community is also very interested in kinematic studies (rather than studies involving simple, qualitative assessment) because these measure provide a lot of useful information about precisely what these children can and can't do. Finally, I'm a big fan of pushing a more recent research agenda, where we don't simply catalogue what children with DCD can't do, but instead, identify more precisely what they can and can't do and look for ways to improve on the things they struggle with. We all know children with DCD have worse movement than typically developing children; the real question is, can we help with these important social skills?


  1. Sounds interesting. Glad to see more research being done concerning fundamental movements, especially with children that have cooridnative disorders. Has there been any prior movement developmental research carried out in people with DCD that will help aid this study?

  2. Not that we've found yet. There are studies on throwing in children, but the vast majority of them use qualitative movement classification schemes, rather than kinematics. I don't think we have any kinematic studies with children with DCD, although my colleague is still looking.

    I've done kinematic analyses on children with DCD before (eg Elders et al, 2010) so at the very least I'm familiar with some of the problems we'll have (their movement data is, by definition, very noisy and erratic!)

  3. Well it's a step in the right direction! I look forward to further findings and wish you all the best.