Kicking is a skill where the foot is used to impart force to a ball so that it is directed towards a target. The ability to kick a stationary ball begins around 18 months of age, and children can kick a moving ball soon after they learn to begin to run. Kicking involves segmental and limb coordination. It involves interception coordination. And it also involves movement coupling that is running with kicking. The goal is to interface segmental and limb coordination with interception coordination and movement coupling to ensure the optimal body and foot positioning along with the appropriate power. The accuracy component involves the coordination variables, and the power component involves the control variables. Accuracy and power can work against each other, unfortunately. So typically, training begins with teaching accuracy. This is the coordination component and the easiest to learn, and then the focus is on enhancing power, the control component. And it's important to realized that practice and not chronological age correlates with effective coordination and control. Research done by Anderson and Sideaway demonstrates how practice of a skill affects both coordination and control. Novice players performing a soccer right-footed instep drive at a two-meter target placed five meters from the ball where compared with expert players. The red solid line shown here illustrates the knee and hip angle interaction and indicates the patterns of coordination of the expert player. This is the approximate point of ball contact. And here is the plot of the hip and knee angles of novice players before practice. That is the straight blue solid line. And this is the angle profile after ten weeks of practice, the dotted blue line. And this is the approximate point of ball contact for the novices. Now you can see that after ten weeks, the novice players were already showing a similar knee and hip angle pattern as the experts, although there was a slight difference in the magnitude of knee flexion and hip extension. The novices still don't have the same range of movement as the experts do after ten weeks of practice, but the overall coordination pattern is similar. And this is a common phenomenon. Ranges of movement at the joints of the legs and torso are small at the early stages of practice and increases with practice. In essence, the novice hip and knee sequence becomes more expert-like after practice. Now here's a graphic illustrating the angular velocity of the novice hip and knee. This is a control variable. And this is the plot of the data for the hip and knee angular velocities before practice. Ball contact occurs about this point here. Now we're going to add the expert hip and knee velocities that are shown in red. And the dotted line are the plots of the knee velocities, and the solid red line are the plots of the hip velocities. I faded the novice plots into the background here. Before practice, novices are less than optimal when you compare them with the experts. The knee velocity of the novices is particularly slow. This is the black dotted line, remember, is the novice, and the red dotted line is the expert. And here are the data after ten weeks of practice. This time I've faded the experts into the background, and the novice are in solid black plots. The novices remain relatively slow with the knee speed, and their hip speed slows down when it should be accelerating. In other words, the timing of the hip and the knee of the novice is not even close to being optimal even after ten weeks of practice. Faster learning of the coordination pattern followed by a slower learning of the control pattern is why beginners improve very quickly into the intermediate stage, but then they become stuck there. They have the pattern of the movement skill down, but improving the control so the power is optimized is a more difficult task. It is the control factor that distinguishes novices from the skilled performer.