Trunk Postural Muscle Timing Is Not Compromised In Low Back Pain Patients Clinically Diagnosed With Movement Coordination Impairments

Abstract

Trunk muscle timing impairment has been associated with nonspecific low back pain (NSLBP), but this finding has not been consistent. This study investigated trunk muscle timing in a subgroup of patients with NSLBP attributed to movement coordination impairment (MCI) and matched asymptomatic controls in response to a rapid arm-raising task. Twenty-one NSLBP subjects and 21 matched controls had arm motion and surface EMG data collected from seven bilateral trunk muscles. Muscle onset and offset relative to deltoid muscle activation and arm motion, duration of muscle burst and abdominal-extensor co-contraction time were derived. Trunk muscle onset and offset latencies, and burst and co-contraction durations were not different (p > .05) between groups. Patterns of trunk muscle activation and deactivation relative to arm motion were not different. Task performance was similar between groups. Trunk muscle timing does not appear to be an underlying impairment in the subgroup of NSLBP with MCI.

Keywords: Low back pain; feedforward postural adjustment; motor control; trunk muscle function.

Figures

Figure 1

Schematic representation of automatic determination of muscle onset, offset and kinematic phases (BIN I-III) of arm perturbation for an individual trial. The filtered EMG signal is displayed for all 14 muscles in red with individual onset and phasic offset times; Ips, ipsilateral; Cont, contralateral (with respect to dominant arm); TrA/IO, transversus abdominis/ internal oblique; EO, external oblique; EO2, external oblique 2; RA, rectus abdominis; LM, lumbar multifidus; LES, lumbar erector spinae; TES, thoracic erector spinae; Arm DIS, arm displacement; Arm VEL, angular velocity segmented into 3 phases: Bin I - auditory trigger to onset of arm movement, Bin II - onset of arm movement to maximum arm velocity, and Bin III - maximum arm velocity to zero arm velocity at maximum arm flexion angle.

Figure 2

Mean and standard deviation of individual trunk muscle onset latencies by group. Y-axis represents onset latency in ms and X-axis represents trunk muscles (TrA/IO, transversus abdominis/ internal oblique; EO, external oblique; EO2, external oblique 2; RA, rectus abdominis; LM, lumbar multifidus; LES, lumbar erector spinae; TES, thoracic erector spinae). 0 ms represents anterior deltoid onset time. Red line at 50ms denotes feedforward cut off. Any trunk muscle onset latency below 50ms is considered feedforward activation and above 50ms is considered feedback activation. Yellow line represents the start of arm movement for NSLBP group and Green line represents the start of arm movement for Controls with respect to anterior deltoid onset.

Figure 3

Mean and standard deviation for trunk muscle offset latencies by group. Y-axis represents trunk muscle offset latencies in milliseconds and X-axis represents trunk muscles (TrA/IO, transversus abdominis/ internal oblique; EO, external oblique; EO2, external oblique 2; RA, rectus abdominis; LM, lumbar multifidus; LES, lumbar erector spinae; TES, thoracic erector spinae)

Figure 4

Mean and standard deviation for trunk muscle phasic burst duration by group. Y-axis represents phasic burst duration in milliseconds and X-axis represents trunk muscles (TrA/IO, transversus abdominis/ internal oblique; EO, external oblique; EO2, external oblique2; RA, rectus abdominis; LM, lumbar multifidus; LES, lumbar erector spinae; TES, thoracic erector spinae).

Figure 5

Illustration of phases (BIN I [feedforward], II, and III [feedback]) and individual trunk muscle onset (black circles) and offset (white circles) times, by group mean and standard deviation. X-axis represents time in seconds. (A) Control (B) NSLBP. Sagittal component of the angular velocity was segmented into 3 phases: BIN I, BIN II/acceleration phase, and BIN III/deceleration phase; Deltoid Bin (−150ms to +50ms from deltoid onset); (TrA/IO, transversus abdominis/ internal oblique; EO, external oblique; EO2, external oblique2; RA, rectus abdominis; LM, lumbar multifidus; LES, lumbar erector spinae; TES, thoracic erector spinae).