There's an optimal coordinated pattern to performing movement units of all skills. Some seemingly diverse skills for have a common goal such as launching and implement, have a similar optimal movement pattern. Throwing and striking for example, involve roughly the same order of moving the appropriate body parts. The sequence begins with the ground and feet and then the hips followed by the shoulders the arms. And then the hands with the implementers finally ejected it's a bit like launching a satellite on top of a five stage rocket the hardest work is done immediately at launch and for this reason the biggest thrust of force is needed for this stage. When throwing or hitting the legs are analogous to the rocket's main stage to provide the initial force for setting the entire mass of the body into motion. Stage two are the hips, stage three is the shoulders, stage four the arms and stage five the hand. Each sequential body part is slightly lighter than one preceding it. The precise timing of the forces produced at each stage sum together to produce the final high velocity needed to project the implement toward its target. Now, this chart here illustrates the correct sequence of body movements for a baseball swing. The correct sequence includes hip rotation first, and this is followed by shoulder rotation, and then, the arm, and finally wrist extension. A bad swing begins with shoulder rotation and then hip rotation, and then extension. And this is a common pattern seeing with novice staff, athletes. The tennis serve, the golf swing, and throwing all use the same sequence of hips first, shoulder, and then arm extension. However, coordinating the correct sequence of body parts is just one aspect of performing a skill effectively. There is also a control component. Performing the correct relative pattern of body parts and movement units is the coordination aspect. And optimizing the motor unit firing so the velocity of each body part is summed at each stage to ensure maximum velocity at the final stage is just as important. And this is the control component, an effective outcome of a skill requires both coordination and control. The counter movement vertical jump provides an example of how both coordination and control is used to maximize the jump. This jump begins with a downward motion and this is followed by the vertical jump. So here's the counter movement. And this is the propulsion phase. The correct relative motion between the body segments for the counter movement vertical jump begins with simultaneous flexion of the hips, knees and ankles in the counter movement phase. And this is followed by simultaneous extension of the hips, knees and ankles in the propulsion phase. Now a normal three to four year old child can easily perform the sequence when asked to jump really high when starting from a standing position. However, a child lacks the muscular control, and is unable to precisely time motor unit firing to produce maximum takeoff velocity. A more skilled performer can optimize body segment movement so that velocity at takeoff is maximized. And therefore the height jumped is maximized. And for this to happen, two things must occur. The first is to ensure a maximum center of gravity height at takeoff. And this is H1 in this graphic. And this occurs if the range of motion of the hips, knees, and ankles is maximized during the counter movement phase to optimize the time of force application against the ground. The second is to obtain maximum vertical velocity of the center of gravity at the very instant of takeoff. And there's a direct relationship between takeoff velocity and how high the center of gravity lifts off the ground. The height the center of gravity rises off the ground is indicated here by H2. And this in turn is dictated by the strength of the extensor muscles of the hips, knees, and ankles. The longer the time producing the force, the higher the takeoff velocity will be. Time of force application depends on the extent to which the available range of motion of the hips Knees and ankles as used. A restricted range of motion adversely affects the ability of the athlete to produce vertical forces. And the result is a lower than optimal jump height. When comparing children with experienced athletes, there's no difference in the coordination variables. However, there are significant differences in the control variables. Children are not able to optimize motor unit firing pattern to achieve the ultimate goal of maximizing their jumping height. A comparison of highly skilled athletes with lesser skilled athletes reveals the same pattern. There is no difference in their coordination, that is their ability to perform the correct sequence of movements are the same. Their performance difference is due to the inability of the less skilled athlete to optimize the relative motion of the body segments due to ineffective motor uniform firing patterns within the appropriate muscles.
