2.2.1 Basic postures
In the basic standing posture, the subject stands erect with feet together (see Fig. 2.7A). The shoulders are relaxed, and the arms are hanging down naturally.
The head is oriented in the Frankfurt plane; that is, the Frankfurt plane of the subject is horizontal. The Frankfurt plane is defined using three landmarks of the head, the right tragion, left tragion, and left orbitale (Fig. 2.2). The orientation of the head affects the accuracy of measurements such as the height and neck girth. The tragion is the notch just above the tragus. The orbitale is the lowest point on the lower edge of the orbit (eye socket), which can only be located by palpation. The three landmarks should be marked in advance, and the measurer should confirm that the line Fig. 2.1 Flow diagram of anthropometry. Manual procedures are shown initalics.
connecting the left tragion and the left orbitale is horizontal just before taking a mea-surement. In the basic sitting posture, the subject sits erect with thighs fully supported by a hard horizontal plane. The head is oriented in the Frankfurt plane. Proper instruc-tions are necessary to ensure that the subject maintains the proper posture during the measurement.
2.2.2 Measuring instruments
The instruments that are used in traditional anthropometry are calibrated in millime-ters. Measurements are read to the nearest millimeter except small measurements of the head, hand, or foot. Fig. 2.3 shows the main instruments used in traditional methods.
The anthropometer and tape measure are usually used in anthropometry for gar-ment design. The anthropometer is used to measure a vertical distance from the floor to a specific landmark. Four rods are put together to make an anthropometer (Fig. 2.3A), and a straight arm is inserted into the cursor. The measurer holds the rod of the anthropometer vertical, slides the cursor, and places the tip of the arm on the target landmark. The measurer should keep the tip of the arm away from the eyes of the subject.
A large sliding caliper consists of one or two rod(s) of the anthropometer and two arms (Fig. 2.3B, left). It is used for measuring large distances between two landmarks and for breadth and depth measurements. Curved arms are used instead of straight arms when necessary (e.g., measuring the chest depth in the midsagittal plane).
The length of the two arms must be the same except when the projected distance between two landmarks is measured.
Fig. 2.2 Frankfurt plane (or, orbitale; tr, tragion).
A sliding caliper is used to measure small breadth measurements and the distance between two landmarks (Fig. 2.3C). Pointed-tip jaws should not be used to measure living people.
A spreading caliper is used to measure the distance between two landmarks when two tips of a sliding caliper cannot touch the landmarks because a part of the body is in the way, such as chest depth in the midsagittal plane and head length (Fig. 2.3D). The large sliding caliper with curved arms can be used for the same purpose.
A tape measure is used for measuring the girth and surface distance. The material of a tape measure should not stretch by tension or by wetting. The tape measure should be cleaned with alcohol as necessary. When a tape measure is wrapped around a subject,
(E)
(C) (D)
(A) (B)
Fig. 2.3 Traditional instruments: (A) anthropometer, (B) large sliding caliper, (C) sliding caliper, (D) spreading caliper, and (E) tape measure.
(A) and (B) are from Mochimaru, M., Kouchi, M., 2006. Biomechanism Library. Measurement of Man: Size, Shape and Motion. Tokyo Denki University Press, Tokyo (in Japanese).
the zero point of the tape measure should overlap the scale on the tape measure as shown in the left image inFig. 2.3E.
An inclinometer is used to measure the shoulder slope. Place the inclinometer on the shoulder line (see “Armscye line” inSection 2.5.5) with an end of it at the side neck point, and read the angle. Prepare two inclinometers, and measure the right and left sides simultaneously when both sides are measured.
2.2.3 Role of the measurer
In traditional methods a measurer and an assistant work together to take measure-ments. The measurer and assistant must be female when the subject is a female. When the subject is a male, a measurer of the same sex is preferable. Measurers should be properly trained before starting a survey to obtain accurate measurements in minimal time. The training includes lectures on basic anatomy for understanding landmark locations, definitions of landmarks and measurement items, measurement errors, and physical training of landmarking and measurements with several subjects with different body shapes.
The measurer is in charge of the measurement process. She/he must decide and mark the locations of landmarks, give proper instructions to the subject for maintaining the correct posture, give proper instructions to the assistant, and take actual measurements.
2.2.4 Role of the assistant
The assistant records the measured value in the correct cell of a data sheet. She/he should repeat the value aloud before writing it down in order to avoid mistakes. If the assistant realizes that the value is unusual, she/he must ask the measurer to take another measurement. The assistant helps the measurer by checking the posture of the subject that is not visible to the measurer (orientation of the head, rotation of the torso, etc.), checking the orientation of the anthropometer (the anthropometer should be ver-tical), holding the tape measure at the back of the subject, and passing the small arti-cles necessary for landmarking or measurement to the measurer (Fig. 2.4). To minimize the time for measurement, the assistant should be aware of what she/he should do without instruction from the measurer.
2.2.5 Measurement errors
The accuracy of measurements is affected by factors related to the instrument, the measurer, and the subject. In traditional methods the instruments are simple and easy to calibrate. The accuracy in landmarking and measurements depends on the skill of the measurer. A proper measuring posture and its repeatability are subject-related fac-tors. However, posture is a part of the definition of a measurement item and can be controlled by proper instruction from the measurer. Since measurements are taken quickly, the effect of body sway is negligible. Therefore the skill of the measurer is the main cause of errors in traditional methods.
Suppose a measurer performed a 1-D measurementx of N subjects. The measure-ment of theith subject, xi, is described as Eq.(2.1), whereM is the mean of N subjects, siis the characteristic of theith subject, o is the effect of the measurer, and eiis the random error.
xi¼ M + si+o + ei (2.1)
Since the mean of the random error is 0, the mean of the subject population will be M + o; that is, the effects of random errors are canceled out, but the effect of the observer remains as a bias. On the other hand the variance of random errors is not 0. Therefore the variance of x is larger than the between-subject variance.
One of the purposes of training measurers is to reduce the random error of each measurer. The variance of random errors by a specific measurer can be calculated from two repeated measurements ofN subjects using Eq.(2.2), wherex1andx2are the first and the second measurement of each subject, respectively:
V e½ ¼X x1 x2
ð Þ2=2N (2.2)
The square root of the random error variance is called the technical error of measure-ment and is one of the indicators of the degree of repeatability of measuremeasure-ments by a measurer.
When multiple measurers participate in an anthropometric survey, systematic dif-ferences (or biases) between measurers also increase the variance. Interobserver error, the difference between measurements taken by two different measurers, depends on the magnitude of the bias and the magnitude of the random error by each measurer.
The interobserver error is larger than the intraobserver error due to the systematic bias between the two measurers. Another purpose of training is to reduce the bias between Fig. 2.4 Possible roles of the assistant: check the posture of the subject and orientation of the instrument, record measurements, and hold the tape measure.
measurers to an allowable range when plural measurers participate in an anthropomet-ric survey. A common understanding of locations of landmarks on the body between measurers is most important for reducing the bias. A practical protocol for locating a landmark helps to reduce both bias between measurers and random error within a mea-surer. A protocol established in ISO 20685-1 (seeSection 2.5) can be used for eval-uating if the differences between measurements taken by two measurers are within an acceptable range.