Movement Control and Motor Unit Behavior Responses to Different Types of Stimulation

The subject will receive the tDCS using 5X7 cm electrodes. The anodal electrode will be placed on M1 representing the back muscles (1 cm anterior and 4 cm lateral to the vertex), while cathodal electrode will be placed on contralateral supraorbital area. The intensity will be set at 2 mA with 10-second fade in/out. The subject will be stimulated by tDCS for 20 minutes

The participants will receive the NMES using interferential mode (6000 Hz, beat frequency 20-50 Hz, scanning effect) on bilateral LM. The intensity will be set at the subject's maximum tolerance. Stimulation will be set at 10 seconds on and 60 seconds off to minimize muscle fatigue. The total NMES time is 20 minutes.

The participant will be instructed to perform co-contraction of transverse abdominis and lumbar multifidus muscle, while performing self-selected pace forward bend. Emphasis will be given to move in control manner (smooth and symmetrical movement). The participant will perform 4 minutes of continuous movement for 4 sets with 1 minute rest between sets.

The participant will be instructed to perform isometric back extension exercise in modified Sorensen position. The participant will hold 60 seconds in neutral position for 5 repetitions with 3 minutes rest between repetitions.