EFFECT OF PAIN ATTENTION/DISTRACTION AND PAIN-RELATED PSYCHOLOGICAL VARIABLES ON NEUROMUSCULAR RESPONSES DURING RAPID ARM FLEXION MOVEMENTS Larivière C 1,2, Butler H 3, Sullivan MJL 2,4, Fung J 2,4, Vadeboncoeur R 2 1 Occupational Health and Safety Research Institute Robert-Sauvé, 2 Centre for Interdisciplinary Research in Rehabilitation of Greater 3 4
Montreal, Canada Montreal, Canada. University of Dalhousie, Halifax, Canada; McGill University, Montreal, Canada E-mail:
[email protected]
AIM: Abnormal (late) feedforward activation of trunk muscles (e.g. transversus abdominus or TrA), has been repeatedly substantiated in chronic low back pain (CLBP) patients using rapid arm flexion movements. The level of pain attention and the psychological profile of the patients are potential candidates to influence these abnormal neuromuscular responses. This study examined the effect of pain attention and variables related to CLBP (pain intensity, kinesiophobia, catastrophizing) on the feedforward activation of trunk muscles. METHODS: 59 patients (30 men) with non-specific CLBP performed rapid arm flexion movements during six conditions (block-randomized; 5 trials per condition) manipulating their attention: (1) self-initiated (control) (2) self-initiated + pain recall (focused on their pain), (3) react to a light stimulus, (4) react to a light stimulus involving a 2-choice reaction (left light = left arm; right light = right arm) (5) two-digit and (6) four-digit recall. Conditions 3 to 6 involved different distraction levels. Surface electromyographic (EMG) signals were recorded on the right deltoid and bilaterally on four back muscles (at L4, L3, L1, T10 levels) and three abdominal muscles (rectus abdominis – RA, tranversus abdominis/internal oblique TrA/IO, external oblique - EO). 3D angular kinematics of the right upper arm and lumbar spine was also measured with inertial sensors. Between-group comparisons were carried out with patients divided in subgroups (high and low scores) based on a median split of scores on pain intensity (10-cm visual analog scale – VAS), fear of movement (Tampa scale of kinesiophobia – TSK), or pain catastrophizing (Pain catastrophizing scale – PCS). RESULTS: The upper-arm kinematics (angular position and velocity) was comparable (P > 0.05) across the different patient subgroups and between the six conditions. Feedforward activation of trunk muscles (relative to right deltoid) was not influenced by focusing attention to pain (condition 2). Among the distraction conditions, the responses were delayed (20-35 ms) for some muscles (L5 right, L1 and T10 left; TrA/IO left) but only in condition 4 (2choice reaction) relative to conditions 1 and 2. Between-group differences were obtained (n = five cases), involving different subgroups (VAS,TSK, PCS) and muscles (L5 right and left, RA, EO and TrA/IO left), the subgroups having the lowest scores always showing delayed activity (16-29 ms) relative to subgroups having higher scores. Lumbar maximal flexion following the perturbation (3.5 ± 2.4°) was not affected by the independent variables. CONCLUSION: Pain-related variables (VAS, TSK, PCS) and pain attention did not affect the task performance (kinematics analyses). EMG results suggest that a part of the delayed feedforward activity previously shown in CLBP patients might be partly explained by attentional disruption. However, it appears that the distraction must be strong enough to have an effect (significant only for the more complex distraction condition). The between-group differences were unexpected and remain to be explained. ACKNOWLEDGEMENTS: Co-funded by the REPAR-FRSQ and IRSST.
