Fig 1.
Placement of surface electromyography electrodes on abdominal muscles and an accelerometer on the thigh.
This figure presents the placement of sEMG electrodes and the accelerometer used in the study. Electrodes were positioned as follows: rectus abdominis (RA), 1 cm superior and 2 cm lateral to the umbilicus; external oblique (EO), 1 cm superior to the horizontal umbilical line and 1 cm lateral to the RA border; and internal oblique/ transversus abdominis (IO/TrA), 1 cm medial to the anterior superior iliac spine (ASIS) and 0.5 cm inferior to the ASIS line. Electrodes were placed on both the right and left sides, giving a total of six sEMG channels. The accelerometer was positioned on the anterior mid-thigh of the right femur.
Fig 2.
Experimental setup and lower limb lowering task performed under three velocity conditions.
This figure presents the testing posture and movement sequence used in the study. Participants lay supine with both hips and knees flexed to 90°, with an inflatable pressure-biofeedback unit (PBU) secured around the L4–L5 region and inflated to 40 mmHg (starting position). While keeping the PBU reading within 40 ± 10 mmHg to maintain lumbar alignment, each participant lowered the right leg until the heel hovered 12 cm above the floor. The descent was executed at three preset velocities—slow (5 s), medium (3 s), and fast (1 s)—administered in randomized order.
Table 1.
Phase segmentation for each movement velocity condition (slow, medium, fast).
Table 2.
Surface electromyography amplitudes expressed as a percentage of maximal voluntary contraction (%MVC) for trunk muscles across velocities and time windows.
Table 3.
Three-way repeated-measures ANOVA: Interaction effects. Factors: Velocity, Phase, and Side on log10-transformed %MVC data for each muscle (IO/TrA, EO, RA).
Table 4.
Three-way repeated-measures ANOVA: Main effects. Main effects from the same three-way repeated-measures ANOVA (Velocity, Phase, Side) presented in Table 3.
Fig 3.
Representative raw surface electromyography (sEMG) waveforms This figure presents representative raw surface electromyography (sEMG) waveforms from a single participant during the Sahrmann Core Stability Test (SCST) Level 3, performed at three different movement velocities (slow, medium, and fast).
The vertical axis represents muscle activity amplitude (mV), while the horizontal axis denotes time (ms), with 0 ms defined as the onset of limb movement. Waveforms are divided into five phases: pre-500 ms (−500 to −251 ms), pre-250 ms (−250 to −1 ms), and three post-movement phases corresponding to the first third (post 1), middle third (post 2), and final third (post 3) of the movement. Each phase is marked by solid lines. Muscle abbreviations: RA (rectus abdominis), EO (external oblique), IO/TrA (internal oblique/transversus abdominis). These waveforms illustrate the performance of a single participant and do not represent the group average.