Many kinesiology professionals are interested in the coordination of movement. Coordination is commonly defined as the sequence and timing of body actions used in a movement. Unfortunately there is no universally agreed-upon definition or way to study coordination in the kinesiology literature. A wide variety of approaches has been proposed to describe the coordination of movement. Some approaches focus on the kinematics of the joint or segmental actions (Hudson, 1986; Kreighbaum & Bartels, 1996), while others are based on the joint forces and torques (kinetics) that create the movement (Chapman & Sanderson, 1990; Prilutsky, 2000; Putnam, 1991, 1993; Roberts, 1991; Zajac, 1991). This section presents the Coordination Continuum Principle, which is adapted from two kinematic approaches to defining coordination (Hudson, 1986; Kreighbaum & Bartels, 1996), because teachers and coaches most often modify the spatial and temporal aspects of movement. While teaching cues that focus on muscular effort may be used occasionally, much of the and coaching of movement remains in the positioning and motions of the body.
Kinematic coordination of movements can be pictured as a continuum ranging from simultaneous body actions to sequential actions. The Coordination Continuum Principle suggests that movements requiring the generation of high forces tend to utilize simultaneous segmental movements, while lower-force and high-speed movements are more effective with more sequential movement coordination. A person lifting a heavy box simultaneously extends the
hips, knees, and ankles (Figure 5.14). In overarm throwing, people usually use a more sequential action of the whole kinematic chain, beginning with the legs, followed by trunk and arm motions.
Because coordination falls on a continuum and the speed and forces of movement vary widely, it is not always easy to determine what coordination pattern is best. In vertical jumping, resistance is moderate and the objective is to maximize height of takeoff and vertical velocity. While a vertical jump looks like a simultaneous movement, biomechanical studies show that the kinematics and kinetics of different jumpers have simultaneous and sequential characteristics (Aragon-Vargas & Gross, 1997a; Bobbert & van Ingen Schenau, 1988; Hudson, 1986). Kinesiology professionals need to remember that coordination is not an either/or situation in many activities. Until there is more research determining the most effective technique, there will be quite a bit of art to the coaching of movements not at the extremes of the continuum.
The motor development of high-speed throwing and striking skills tends to begin with restricted degrees of freedom and simultaneous actions. Children throwing, striking, or kicking tend to make initial attempts with simultaneous actions of only a few joints. Skill develops with the use of more segments and greater sequential action. In high-speed throwing, for example, the sequential or "differential" rotation of the pelvis and upper trunk is a late-developing milestone of high-skill throwing (Roberton & Halverson, 1984). It is critical that physical educators know the proper sequential actions in these low-force and high-speed movements. Kinematic studies help identify these patterns of motion in movement skills. Unfortunately, the youth of biomechanics means that kinematic documentation of coordination in the wide variety of human movements is not complete. Early biomechanics research techniques emphasized elite male performers, leaving little information on gender, special populations, lower skill levels, or age.
Suppose a junior high volleyball coach is working with a tall athlete on spiking. The potential attacker lacks a strong overarm pattern and cannot get much speed on the ball (Figure 5.15). The kinematics of the preparatory action lacks intensity, stretch, and timing. At impact the player's elbow and upper arm are well forward of her shoulder. The coach suspects that her overarm throwing pattern is still immature and must be developed before skilled spiking is possible. This coach has integrated biome-chanical and motor development information to determine the best course of action to help this player improve. The lack of ball speed (kinematics), and muscle stretch-shortening cycles within a sequential coordination are biomechanical factors missing in this athlete. The forward elbow position at impact is a motor development indicator
of an immature trunk and arm action within an overarm pattern. How coaches work on this problem may vary, but one good strategy would be to simplify the movement and work on throwing the volleyball. Sequential rotation of the trunk, arm, forearm, and wrist is the focus of training.
Strength and conditioning professionals closely monitor training technique, because body position and motion in exercises dramatically affect muscular actions and risk of injury. In strength training, resistances are near maximal, so coordination in most exercises tends to be simultaneous. Imagine someone performing a squat exercise with a heavy weight. Is the safest technique to simultaneously flex the hips and knees in the eccentric phase and then simultaneously extend in the concentric phase? If the resistance is lighter (body-
weight), like in standing up out of a chair, after a person leans forward to put their upper bodyweight over their feet, do the major joints of the body simultaneously act to stand? In the next chapter we will examine variations in conditioning for high-power and high-speed movements that are different than high-force (strength) movements. Do you think high-power movements will also have simultaneous coordination, or will the coordination shift a little toward sequential? Why?
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