16 2.4 Human Dimensions and Joint Angles
It is sometimes important to know the person you are assessing’s height or limb length. The following are brief description of the measurements:
Height (Length)
Height is a common body measurement typically measured in meters (m) or centimeters (cm). These are length measurements, so the SI unit would be meters. Height is typically measured with the participant standing straight, near a wall, with both feet flat on the ground.
Segment Length
Segments are measured in centimeters (cm) or millimeters (mm). Each segment (limb) is measured by identifying bony protuberances on each end of the segment. For example, the length of the tibia is measured from the medial condyle at the knee to the medial malleolus at the ankle. The fibula would be measured from the head of the fibula at the knee to the lateral malleolus at the ankle.
Joint Angles
Biomechanists quantify different types of joint angles:
- Relative – This represents the angle between two segments. It can also be called a joint angle. For example, the angle between the shank (lower leg) and foot is called the ankle angle. There are two sub-types:
- Included: The absolute angle between two segments
- Anatomical: The angle between two segments relative to the anatomical position.
- Absolute – An absolute angle, also called a segment angle, is the angle of a segment relative to the perfect horizontal. It is calculated by drawing a horizontal line at the distal end of the segment and measuring the angle from the right horizontal to the segment in a counterclockwise direction.
Range of Motion
Range of motion is a common body measurement, especially while diagnosing injury or disease, tracking progress during physical therapy, or working to improve flexibility or form. It is usually measured with a goniometer. Range of motion is calculate in each plane of movement respectively (sagittal, frontal or transverse). Range of motion can be defined as an angle measured in degrees (°)through which a joint moves away from a reference position as seen in this video demonstration of how to use a goniometer for range of motion measurement. It can also be measured as the difference between two extremes of motion (relative abduction vs adduction angle for example).
For example, to calculate the total range of motion at the knee in the sagittal plane you measure the angle between the thigh and the lower leg (knee angle) at full extension. You then measure the same knee angle at full flexion. The difference between full extension and full flexion, represents the range of motion at the knee.
Range of motion is an important predictor of injury prevention and performance in many sport. For example, the range of motion at the Hallux (the big toe) should be 75-85 degrees for extension and 35-45 degrees for flexion. A reduction in range of motion can lead to pain (toe, knee and hip) and difficulty with certain activities such as squatting and running. An ideal range of motion was established for each joint and can be found in Physical Therapy manuals.
Reinforcement Activity
What range of motion do you have at the shoulder? Is the range of motion on your left side the same as your right? How could you explain a difference between the range of motion of the right and left side?