Table 1 Methods for positions of interest muscles and EMG signals

Transversus Abdominis (TA)

Subjects were seated upright against the wall with one hand holding the sphygmomanometer gauge and both feet rested on the floor. The pressure cell was placed behind the lumbar spine. Subjects slowly pulled their lower abdomen and navel towards the back to contract TA without changing spinal position change [11, 14]. The PBU pressure of 50 mmHg, 60mmHg and 70mmHg were selected in random order.

Multifidus (MF)

Subjects were seated uprightly against the wall with one hand holding the sphygmomanometer gauge and both feet rested on the floor. The pressure cell was placed behind the medial edges of the shoulder blades. Subjects slowly extended the lumbar spine to contract MF [18, 20], until the PBU pressure reached 50 mmHg, 60mmHg or 70mmHg.