Rangeofmotion Principle

One area where anatomical description is quite effective is in the area of the range of

Application: Muscle Groups

If muscles create movement in complex synergies that are adaptable, should kinesiology professionals abandon the common practice of naming muscle groups according to anatomical function (quads [knee extensors] or calf [ankle plantar flexors])? Such an extreme reaction to the complexity of biomechanics is not necessary. This common terminology is likely appropriate for prescribing general strength and conditioning exercises. It may even be an appropriate way to communicate anatomical areas and movements in working with athletes knowledgeable and interested in performance. Kinesiology professionals do need to qualitatively analyze movements at a deeper level than their clients, and remember that this simplified terminology does not always give an accurate picture of how muscles really act in human movement. Biomechanical and other kinesiolo-gy research must be integrated with professional experience in qualitatively analyzing movement.

motion used in movement. Movement can be accurately described as combinations of joint angular motions. Remember that the biomechanical principle of range of motion, however, can be more generally defined as any motion (both linear or angular) of the body to achieve a certain movement goal. Specific joint motions can be of interest, but so too can the overall linear motions of the whole body or an extremity. Coaches can speak of the range of motion of a "stride" in running or an "approach" in the high jump. Therapists can talk about the range of motion for a joint in the transverse plane.

In human movement the performer can modify the number of joints, specific anatomical joint rotations, and amount of those rotations to tailor range of motion. Range of motion in movement can be imagined on a continuum from negligible motion to 100% of the physically possible motion. The Range-of-Motion Principle states that less range of motion is most effective for low-effort (force and speed) and high-accuracy movements, while greater range of motion favors maximum efforts related to speed and overall force production (Hudson, 1989). A person playing darts "freezes" or stabilizes most of the joints of the body with isometric muscle actions, and limits the dart throw to a small range of motion focused on elbow and wrist. The javelin thrower uses a long running approach and total body action to use considerable range of motion to maximize the speed of javelin release. The great accuracy required in golf putting favors limiting range of motion by using very few segments and limiting their motion to only what is needed to move the ball near the hole (Figure 3.15).

The application of the range-of-motion principle is more complicated when the effort of the movement is not maximal and when the load cannot be easily classified at the extremes of the continuum. A baseball or softball seems pretty light, but where on the range-of-motion continuum are these

Figure 3.15. Very accurate movements like putting in golf limit range of motion by freezing most segments and using only a few segments. Photo courtesy of Getty Images.

intermediate load activities? How much range of motion should you use when the load is a javelin, a shot, or your bodyweight (vertical jump)? Biomechanical studies can help kinesiology professionals decide how much range of motion is "about right." In the qualitative analysis of movement, this approach of identifying a range of correctness (like in range of motion) is quite useful because the professional can either reinforce the performer's good performance, or suggest less or more range of motion be used (Knudson & Morrison, 2002). The continuum of range of motion can also be qualitatively evaluated as a sliding scale (Knud-son, 1999c) or volume knob (Hudson, 1995) where the performer can be told to fine tune range of motion by feedback (Figure 3.16). Let's look at how biomechanical research can help professionals evaluate the range of motion in a vertical jump.

The amount and speed of counter-movement in a vertical jump is essential to a high jump. This range-of-motion variable

Figure 3.16. Range of motion can be evaluated and pictured as an analog scale or a volume knob. If a change in range of motion is appropriate, the performer can be instructed to "increase" or "decrease" the range of motion in their movement.

Range of Motion

Figure 3.16. Range of motion can be evaluated and pictured as an analog scale or a volume knob. If a change in range of motion is appropriate, the performer can be instructed to "increase" or "decrease" the range of motion in their movement.

can be expressed as a linear distance (drop in center of mass as percentage of height) or as body configuration, like minimum knee angle. We use the knee angle in this example because it is independent of a subject's height. One can hypothesize that maximizing the drop (range of motion) with a small knee angle in the countermovement would increase the height of the jump; however, this is not the case. Skilled jumpers tend to have minimum knee angles between 90 and 110° (Ross & Hudson, 1997). The potential benefits of range of motion beyond this point seems to be lost because of poorer muscular leverage, change in coordination, or diminishing benefits of extra time to apply force. The exact amount of counter-movement will depend on the strength and skill of the jumper, but coaches can generally expect the knee angles in this range.

Another example of the complexity of applying the range-of-motion principle would be the overarm throw. In overarm throwing the athlete uses range of motion from virtually the entire body to transfer energy from the ground, through the body and to the ball. The range of motion (kinematics) of skilled overarm throwing has been extensively studied. Early motor development studies show that one range-of-motion variable (the length of the forward stride is usually greater than 50% of height) is important in a mature and forceful overarm throw (Roberton & Halverson, 1984). Stride length in throwing is the horizontal distance from the rear (push-off) foot to the front foot. This linear range of motion from leg drive tends to contribute 10 to 20% of the ball speed in skilled throwers (Miller, 1980). The skill of baseball pitching uses more stride range of motion, usually between 75 and 90% of standing height, and has been shown to significantly affect pitch speed (Montgomery & Knudson, 2002).

The axial rotations of the hips and trunk are the range-of-motion links between stride and arm action. The differentiation of hip and trunk rotation is believed to be an important milestone in mature throwing (Roberton & Halverson, 1984), and these movements contribute about 40 to 50% of ball speed in skilled throwers. In coaching high-speed throwing, coaches should look for hip and trunk opposition (turning the non-throwing side toward the target) in preparation for the throw. The optimal use of this range of motion is a coordination and segmental interaction issue that will be discussed later. Students interested in the skilled pattern of hip and trunk range of motion should look at the research on skilled pitchers (Fleisig, Barrentine, Zheng, Escamilla, & Andrews, 1999; Hong & Roberts, 1993; Stodden et al., 2005).

Arm action is the final contributor to the range of motion used in overarm throwing. The complex joint actions of throwing contribute significantly (30-50% of ball velocity) to skilled throwing (Miller, 1980). To take advantage of the trunk rotation, the shoulder stays at roughly 90° of abduction to the spine (Atwater, 1979) and has been called the strong throwing position (Pla-genhoef, 1971). With initiation of the stride, the elbow angle stays near 90° to minimize resistance to rotating the arm, so the major increase in ball speed is delayed until the last 75 ms (a millisecond [ms] is a thousandth of a second) before release (Roberts, 1991). Contrary to most coaching cues to "extend the arm at release," the elbow is typically 20° short of complete extension at release to prevent injury (Fleisig et al., 1999). Inward rotation of the humerus, ra-dioulnar pronation, and wrist flexion also contribute to the propulsion of the ball (Roberts, 1991), but the fingers usually do not flex to add additional speed to the ball (Hore, Watts, & Martin, 1996).

In overarm throwing it appears that the range-of-motion principle can be easily applied in some motions like stride length using biomechanical research as benchmarks; however, it is much more difficult to define optimal amounts of joint motions or body actions in complex movements like overarm throwing. How range of motion might be changed to accommodate different level of effort throws, more specific tasks/techniques (e.g., curveball, slider), or individual differences is not clear. Currently, professionals can only use biomechanical studies of elite and skilled performers as a guide for defining desirable ranges of motion for movements. More data on a variety of performers and advances in modeling or simulation of movement are needed to make better recommendations on how modifications of range of motion may affect movement.

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