Static posture tasks

Firstly, main static postures in daily living were chosen. Two of them including standing and sitting are commonly used in clinical practice when chiropractors record the surface EMG signal from paraspinal muscles (Kelly & Boone, 1998; Kent & Gentempo, 1995; Marcarian, 2002). Four point kneeling posture is commonly used to activate the lumbar paraspinal muscles in rehabilitation programs (Richardson & Jull, 1995). Therefore, four point kneeling posture could be more appropriate than standing and sitting postures to investigate lumbar multifidus muscle activity by surface EMG. Posture-monitoring equipment (Figure 3 – 3) was designed to allow the reproduction of specific static postures in sagittal plane, frontal plane or horizontal plane including four point kneeling, sitting, and standing.

Standing Four point kneeling

Sitting

Figure 3 – 3 : Posture-monitoring equipments

One way to evaluate the functional status of the lumbar paraspinal muscles is to observe the pattern of activity. However, these postures are associated with a low level of muscle contraction in the lumbar region. In order to observe the pattern of muscle activity in the lumbar paraspinal muscles, it is necessary to increase the level of muscle contraction. In this study, subjects were required to raise one arm or both arms during the experiment. This arm raising activity increases the load on the spine. The pattern of activity can be observed at different segmental levels when one or both arms are raised. Consequently, in this study,

eleven static postures were used to record the surface EMG signal from the lumbar paraspinal muscles including four point kneeling with the left arm raised flexion to 90 degrees (4PL), four point kneeling with no arms raised (4PN), four point kneeling with the right arm raised flexion to 90 degrees (4PR), sitting with bilateral arms raised flexion to 90 degrees (SITB), sitting with the left arm raised flexion to 90 degrees (SITL), sitting with no arms raised to 90 degrees (SITN), sitting with the right arm raised flexion to 90 degrees (SITR), standing posture with no arms raised (STAN), standing posture with bilateral arms raised flexion to 90 degrees (STANB), standing with the left arm raised flexion to 90 degrees (STANL), and standing with the right arm raised flexion to 90 degrees (STANR) (Table 3 – 2).

Table 3 – 2: Static posture tasks

Posture Code Posture setting

1 4PL Four point kneeling with the left arm raised flexion to 90 degrees 2 4PN Four point kneeling with no arms raised

3 4PR Four point kneeling with the right arm raised flexion to 90 degrees 4 SITB Sitting with bilateral arms raised flexion to 90 degrees

5 SITL Sitting with the left arm raised flexion to 90 degrees 6 SITN Sitting with no arms raised

7 SITR Sitting with the right arm raised flexion to 90 degrees 8 STAN Standing with no arms raised

9 STANB Standing with bilateral arms raised flexion to 90 degrees 10 STANL Standing with the left arm raised flexion to 90 degrees 11 STANR Standing with the right arm raised flexion to 90 degrees

For all standing postures (STAN, STANB, STANL, and STANR) (Figure 3 – 4), subjects were required to stand on the board naturally with their back against a wall and to lightly touch the wall. Therefore, they were not supported by the wall with their feet approximately shoulder-width apart. Thus, the anatomical point most convex from the body (scapulae and/or thoracic spine) lightly touched the wall. Arms were positioned beside their body. Foot position was marked on a piece of paper using a highlighter pen in order to reproduce the standing posture at the second recording session.

Standing with no arms raised (STAN) Standing with bilateral arms raised flexion to 90 degrees (STANB)

Standing with the left arm raised flexion to 90 degrees (STANL)

Standing with the right arm raised flexion to 90 degrees (STANR)

Figure 3 – 4: Standing posture

For all sitting postures (SITB, SITL, SITN, and SITR)(Figure 3 – 5), subjects were required to sit on the flat platform of chair with no back support which was height adjustable so that the angle formed between the thigh and calf measured 90 degrees. The mechanical pointers were positioned at three anatomical landmark points including the iliac crest, the acromion, and the mastoid process in order to reproduce the positions of these body segments in the sagittal plane during sitting. Hands were placed on their thighs. Foot position was marked on

Sitting with bilateral arms raised flexion to 90 degrees (SITB)

Sitting with the left arm raised flexion to 90 degrees (SITL)

Sitting with no arms raised (SITN) Sitting with the right arm raised flexion to 90 degrees (SITR)

Figure 3 – 5: Sitting posture

For the standing and the sitting postures (STANB, STANL, STANR, SITB, SITL, and SITR), subjects were also required to position the level of flexion 90 degrees on shoulder joint.

Another mechanical pointer was used to reproduce the arm raised position for the second session, and two distances between this pointer and the board against which subjects were lightly touching while standing, and between this pointer and the chair which subjects were sitting. The purpose of one arm or bilateral arms raised flexion to 90 degrees during sitting and standing was to vary the muscle activity of the lumbar paraspinal muscles in order to increase the muscle load. At the end of one minute recording, there may be no muscle fatigue for normal subjects. In this study, firstly initial recording was examined reliability between

different days. When this recording period is reliable, comparison analysis between initial and end recording will be carried out.

Four point kneeling (4PL, 4PN, and 4PR) (Figure 3 – 6) involved the subject assuming a posture where knees and hands were positioned vertically underneath the corresponding shoulder and hip joint. The torso was maintained as flat as possible. Mechanical markers were used to guide the position of the thighs, knees, shoulders and hands. In addition, for 4PL and 4PR, each subject was required to flex their shoulder joint (with a straight arm) to 90 degrees.

In order to reproduce this shoulder flexion for the second session another mechanical pointer was used to measure this height, and distance between this pointer and the board which subjects maintained four point kneeling. The purpose of this arm movement was to alter the lumbar muscle activity, as was the case with the sitting and standing postures.

Four point kneeling with no arms raised (4PN)

Four point kneeling with the left arm raised flexion to 90 degrees (4PL)

Four point kneeling with the right arm raised flexion to 90 degrees (4PR)

Figure 3 – 6 : Four point kneeling posture

In all postures, subjects were required to visually focus on one specific point in order to avoid neck movement during recording.