Trunk neuromuscular pattern alterations during a controlled functional task in a low back injured group deemed ready to resume regular activities.

Background: Trunk neuromuscular alterations have been found in those with chronic low back pain, but less well studied are whether responses are altered in those deemed recovered following an injury. Furthermore, coordinated trunk muscle responses are deemed important for normal spinal function, but there are no studies of temporal patterns early after a low back injury. Determining whether altered trunk muscle patterns exist early after injury could improve our understanding of recovery by providing an objective assessment of functional recovery and risk of re-injury.

Objective: To determine if amplitude and temporal characteristics of trunk neuromuscular patterns differ during a dynamic functional task in a group of participants with recent (within 12 weeks) low back injury (LBI), but deemed ready to resume normal activities, when compared to those with no similar history of injury (ASYM).

Participants: 35 participants in each group (17 females) were matched for age and body mass index (BMI); (ASYM 36 yrs, BMI 26, LBI 39 yrs, BMI 27).

Methods: Participants performed a controlled lifting task (2.9 kg) in a standing maximum reach position, which altered frontal and sagittal plane moments of force. Electromyographic activity of 24 trunk muscle sites, as well as thoracic and pelvis position via an electromagnetic sensor was collected. Principal component analyses extracted the temporal and amplitude waveform patterns. Mixed model ANOVAs tested for effects (p< 0.05) in the main patterns. Preliminary data regarding re-injury status after 1 year was included.

Results: Three principal patterns explained 97% of the variance, with the LBI group demonstrating increased amplitude and a more constant level of activity compared to the ASYM group. The LBI group also demonstrated more thoracic motion in all 3 axes during this highly constrained task. The no re-injury group had lower activation than the re-injury group, but similar temporal patterns.

Conclusions: Despite the perception of readiness to return to work and low pain scores, the temporal and amplitude muscle activation patterns were altered in this LBI group indicating that differences exist compared to a non-low back injured group. The differences are not just relative amplitude differences among muscles but include differences in the temporal response to the flexion moment.