I

Figure 3.2. Orthopedic and pediatric medicine often calls the lower extremity deviation in (a) genu (knee) valgus because the distal segment (lower leg) deviates laterally from the midline of the body. Normal leg orientation in the frontal plane is illustrated in (b). The use of valgus and varus terminology is often inconsistent in the literature and should be clearly defined when used (Houston & Swischuk, 1980).

see that this little problem of anatomical description is very similar to the multiple kinematic frames of reference (chapter 5) that are all correct descriptions of a single motion and the different units of measurement that can be used. Mechanics and anatomy both share the minor problem that there are several standards that have grown up with these sciences since people all over the world have been working on these same problems. Students should strive to read and write with special attention to the meaning of professional/scholarly terminology.

Joint Motions

Anatomy also has specific terminology describing the major rotations of bones at joints. "Flexion" refers to a decrease in joint angle in the sagittal plane, while "extension" is motion increasing joint angle (Figure 3.3a). Motion into the extremes of the range of motion are often noted as "hyper," as in hyperextension. Motion of a segment away from the midline in the frontal plane is "abduction," while movement back toward the midline is called "adduction" (Figure 3.3b). Joint motions in the transverse plane are usually called inward rotation (rotation of the anterior aspect of the segment toward the midline) and outward rotation (Figure 3.4). Some examples of special joint motion terms are "pronation," which refers to internal rotation of the forearm at the radioulnar joint, or "horizontal adduction," which is drawing the shoulder (glenohumeral joint) toward the midline in a transverse plane. Like the directional terms, anatomical terminology related to the rotations of joints is also used incorrectly. It is incorrect to say "a person is flexing a muscle" because flexion is a joint movement. It is important for kinesiology majors to use anatomical terms correctly. Refer to your anatomy book frequently to keep all

Figure 3.2. Orthopedic and pediatric medicine often calls the lower extremity deviation in (a) genu (knee) valgus because the distal segment (lower leg) deviates laterally from the midline of the body. Normal leg orientation in the frontal plane is illustrated in (b). The use of valgus and varus terminology is often inconsistent in the literature and should be clearly defined when used (Houston & Swischuk, 1980).

Adduction Frontal Plane
Figure 3.3. (a) Flexion and extension movements occur in a sagittal plane about a mediolateral axis; (b) adduction/abduction of the hip joint occurs in a frontal plane about an anteroposterior axis.

the joint motion terminology (this section does not review them all) fresh in your mind.

While there are attempts to standardize anatomical description throughout the world (Federative Committee on Anatomical Terminology, 1998; Greathouse et al., 2004), there remain regional inconsistencies in terminology. For example, some refer to the frontal plane as the "coronal" plane. Applied sciences such as medicine often develop specialized terms that are borrowed from anatomy, but that go against anatomical convention. A good example is related to how the foot acts during the stance phase of running. Medical and biomechanical studies have adopted the terms "pronation" and "supination" to refer to the complex triplanar actions of the subtalar joint. In normal running the foot strikes the ground on the lateral aspect of the foot; the combined anatomical actions of eversion, plantar flexion, and abduction in the first part of stance is called pronation. This pronation serves to absorb the shock of the collision of the foot with the ground (Figure 3.5). The opposite motion (supination) stiffens the foot for the push off phase of stance. Here is another example of how anatomical terms are not always used in a consistent way. In your studies of biome-chanics and other kinesiology disciplines, remember that adaptations and variations in anatomical terminology make it important to read carefully and often check background information. Modern biomechani-cal studies often assume quite a bit about reader expertise in the area and may not cite sources giving necessary terminology and background information. This saves

Figure 3.4. Inward and outward rotation of the shoulder joint occurs in a transverse plane about a longitudinal axis.
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