sEMG biofeedback: Subjects were instructed to monitor the sEMG signals of the D/UT balances ratio on the screen and maintain the D/UT balances ratio above the threshold during arm elevation and lowering. The threshold was set at 1 standard deviation of the ratio average at baseline (before intervention).

NMES: Two electrode pads were placed on the anterior, middle, and posterior deltoid boundary lines and at a distance of 1cm distal to the lateral margin of the acromion. The operator palpated the deltoid muscle contraction and asked the subjects to perform arm elevation task with NMES. (frequency of 35 Hz and a duration of 250 microseconds.) A verbal cue was given during both th A verbal cue was given during both the sEMG biofeedback and NMES interventions: "Lengthen your arm as if you want to touch the ground, the scapula keeps in the neutral position, and then elevate your arm." Each intervention consisted of 3 sets of 10 repetitions per set, with a 1-minute rest between sets.

NMES: Two electrode pads were placed on the anterior, middle, and posterior deltoid boundary lines and at a distance of 1cm distal to the lateral margin of the acromion. The operator palpated the deltoid muscle contraction and asked the subjects to perform arm elevation task with NMES. (frequency of 35 Hz and a duration of 250 microseconds.) A verbal cue was given during both th

A verbal cue was given during both the sEMG biofeedback and NMES interventions: "Lengthen your arm as if you want to touch the ground, the scapula keeps in the neutral position, and then elevate your arm." Each intervention consisted of 3 sets of 10 repetitions per set, with a 1-minute rest between sets.

Muscle activation The muscle activation of upper trapezius, lower trapezius, serrates anterior, and deltoid were collected during arm elevation task by sEMG at baseline, post- sEMG biofeedback, and post- NMES. Muscle activation was analyzed based on 0°-30°, 30°-60°, and 60°-90° during arm elevation and lowering. The sEMG data was calculated using the root mean square (RMS) based on average of middle three from five trials. The MVIC of UT, LT, SA, and D were used to normalize the sEMG data.

Scapular kinematics The scapular kinematics during arm elevation task was captured using an electromagnetic motion analysis system. The three scapula orientations were described using the Euler angle sequence with an X-axis for scapular posterior/anterior tilt, Y-axis for scapular upward/downward rotation, and Z-axis for scapular internal/external rotation. The average of middle three from five trials on scapular kinematics were analyzed at 30°, 60°, and 90° arm elevation and lowering.

Muscle balance ratios The muscle balance ratios of D/UT, D/LT, and D/SA were calculated based on average of middle three from five trials at the phases of 0°-30°, 30°-60°, and 60°-90° during arm elevation and lowering phase.