 During verbal instruction, one investigator will give a verbal instruction and then ask the participant to perform a contralateral-arm task, in which the participant will lift the contralateral arm approximately 5 cm above the table and hold for 5 seconds. The verbal instruction was selected based on our published pilot study which showed that this instruction seemed to activate lumbar multifidus muscle the most: Breathe normally, without moving the pelvis or spine, think about tilting the pelvis forward without actually moving it, and lift the left right arm. 