Poster Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION:  Individuals with low back pain (LBP) have impaired lumbopelvic muscle activity and deficits in motor control. A pressure biofeedback unit (PBU) has been used to evaluate and treat the lumbopelvic region in patients with LBP. Previous efforts primarily employed isometric tasks that do not necessarily challenge patients across the range of frequencies encountered during functional activities, which makes inferences into lumbopelvic dynamics difficult. Therefore, this study aimed to assess the test-retest reliability of lumbopelvic motor control performance and muscle activity during both isometric and dynamic pressure tracking tasks, hypothesizing excellent reliability for these tasks.

METHODS:  Sixteen individuals (n=9 women, n=7 men) without LBP participated. All participants signed an IRB-approved informed consent form prior to participation. Participants performed two trajectory tracking tasks: 1) Abdominal Hollowing and 2) Pelvic Tilt. These tasks required participants to track a displayed target (input) by modulating pressure on a PBU using their lumbopelvic muscles. Pressure measurements from the PBU projected the participants’ applied pressure (output) onto a computer monitor for feedback. For both tasks, participants tracked five different target trajectories (inputs): isometric, sine, single-step, multi-step, and chirp. Surface electromyography (EMG) was used to assess the following bilateral muscles: rectus abdominis, external obliques, internal obliques, and lumbar erector spinae. Abdominal Hollowing was performed in the prone position with the PBU placed at the level of the anterior superior iliac spine and Pelvic Tilt was performed in the supine position with the PBU under the lumbar spine. Participants performed all five trajectory-tracking tasks twice during a single visit. These tasks were repeated on a second visit, separated by a minimum of 24 hours, to assess test-retest (between-day) reliability. Performance was measured by the root mean square error (RMSE) of the target (input) and participant’s response (output). Peak EMG was expressed as a percentage of the maximum voluntary isometric contraction (%MVIC). Between-day performance and EMG measures were assessed using dependent t-tests, while test-retest reliability was assessed using Intraclass Correlation Coefficients ICC(3, k). The ICCs were classified as poor (<0.40), fair (0.40-0.59), good (0.60-0.74), or excellent (0.75-1.00). Statistical analyses were performed in SPSS (V.27, Armonk, NY, IBM Corp.) with a significance level set at p<0.05.

RESULTS:  Test-retest reliability for performance ranged from fair to excellent for pelvic tilt (ICC=0.52-0.83; mean ICC=0.72) and poor to excellent for abdominal hollowing (ICC=0.15-0.81; mean ICC=0.56) (Table 1). Test-retest reliability for muscle activity ranged from poor to excellent during pelvic tilt (ICC=0.24-0.92) and poor to excellent during abdominal hollowing (ICC=0.05-0.94) (Table 2). Across both tasks, there was a trend toward significantly better performance (lower RMSE) on the second day for the sine and multi-step input/target trajectories (p=0.001-0.087), suggesting learning effects. In general, lower ICCs were observed in muscles where muscle activity was low.

DISCUSSION:  Reliable measures of lumbopelvic motor control are essential for clinical and biomechanical applications. Based on these findings, the test-retest reliability is dependent on the tasks, input trajectories, and muscles involved. Further research is needed to determine which combination of tasks and inputs are most sensitive to treatment interventions.