Range of motion (ROM) is an aspect of sports science that assists in the determination of how far a particular joint can move. Joint flexibility as defined by the ROM of the particular structure is essential to both injury prevention, as well as measuring rehabilitative progress after an injury. Joints that are capable of an additional range of motion typically permit the athlete to move with greater grace and power. The archetypal "loose-limbed" athlete is the person who possess a greater ROM than the average individual.
ROM is measured by the number of degrees that a joint can be moved without the application of external force from a determined position. The common tool used to perform the measurement is a double-armed goniometer, an instrument used to calculate geometric angles. Each joint, by virtue of its unique structure, has a different optimum ROM. Particular attention is paid by sports scientists to the ROM of the shoulder, elbow, wrist, hip, knee, and ankle; all joints in the body are capable of ROM measurement.
The measurement of shoulder ROM is a complex one, due to the variety of ways that the shoulder is called on to move in different sports. The ROM of the shoulder of a baseball pitcher will bear different considerations than the ROM of the shoulder of a crosscountry skier. The forces directed into the shoulder joint in each sport are significantly different, both in terms of the degree of the force as well as the direction that the shoulder is required to move. For this reason, the shoulder ROM will be determined from a variety of perspectives: abduction, with the arm extended from the body; adduction, with the arm pulled in toward the body; flexion, in a bending motion; extension, in a straightening or extending motion; hyperextension, extending the joint past 180° of motion; and rotation, the movement of the joint in a circular motion, in both clockwise and counterclockwise directions.
With the ROM determined in each of the aspects of shoulder movement, a definitive picture can be drawn regarding the laxity or flexibility of the joint.
In a hinge joint such as the elbow or the knee, the ROM measurement is simplified. The key determination in these joints is the relationship between the flexion (bending) and the extension (stretching). In the elbow, a normal person can bend the elbow sufficiently back that the wrist approximately reaches the ear. If the wrist is moved from a position with the arm extended parallel to the floor, the angle created by the flexion is approximately 140°. If the person is able to extend the wrist past the point where the arm is parallel to the floor, this is described as a hyperextension of the elbow. A small degree of hyperextension is common; any further flexibility in the joint is often described as "double-jointed."
A hyperextension of a joint can also occur through physical contact and result in an injury to the joint, particularly to the ligaments. A hyper-extended position is generally an unstable position for ajoint, one where the ability of the joint to sustain the forces of movement or a direct blow is much reduced. Given the structure of the knee joint, with six sets of ligaments providing support to the joint, a hyperextension of the knee is often one that compromises the strength of the ligament structures, as the joint is forced through a ROM that the ligaments cannot sustain.
Wrist ROM, like that of the shoulder, is measured in more than one direction. The flexibility of the wrist is assessed first from the perspective of wrist flexion, the degree by which the wrist can extend and flex from a position where the wrist is palm down, parallel to the ground. The joint is also observed from the same position, with the movement measured on the ulnar side (the side opposite the thumb, the location of the ulnar bone), and the radial side (the thumb side).
The ROM in the foot is assessed in terms of the joint's dorsi flexion, the amount by which the front of the foot may be flexed upward, and the plantar flexion, the corresponding measurement of how far the toe may be pointed downward.
ROM will be improved in all joints through a focused and dedicated stretching and flexibility program. All athletes will suffer tightness and reduced joint laxity if muscles are subject to forces but the connective tissues to the joints are not adequately stretched. Reduced ROM will tend to limit both the explosive ability of the athlete as well as the agility in the execution of an athletic movement.
In strength training, greater ROM is achieved through work with free weights as opposed to those carried out with stationary machines that limit the ROM required to carry out the exercise. Free weights, used properly, will compel the athlete to value form, which is an alternative expression of greater ROM.