Jo Armour Smith
Background During voluntary limb movement, feedforward postural activation of the trunk and hip musculature occurs to maintain postural stability. This is called an anticipatory postural adjustment (APA). Onset of trunk muscle APAs is delayed in symptomatic individuals with persistent low back pain (LBP). It is not clear how spatial APA organization is affected, or if adaptations in APAs persist between symptomatic episodes. We used two versions of a supine active leg raise task to examine central modulation of APAs. One version of the task, the supported leg raise (SLR) does not elicit trunk/hip APAs. The other, the unsupported leg raise (ULR) elicits APAs in the bilateral abdominals and in the hip musculature contralateral to the moving limb. We hypothesized that individuals with a history of LBP would demonstrate increased amplitude of APA activation in non-fatigued muscles following fatiguing exercise. Methods 40 right-limb dominant adults between the ages of 18 to 35 years participated. The LBP group (n = 25) had a greater than one-year history of functionally limiting low back pain but were in symptom remission at the time of the data collection. The back healthy control group (n = 15) had no history of back pain. Surface electromyography electrodes were placed bilaterally on the internal obliques (IO), external obliques (EO), biceps femoris (HS) and rectus femoris muscles. Ten repetitions of the SLR and the ULR were performed before and after paraspinal fatigue was induced by the isometric Biering-Sorensen endurance test. For the SLR, participants lay supine with the left upper leg supported and extended the knee to touch the ankle to a target. For the ULR, participants raised the entire leg to touch the ankle to the target. The ULR was performed both at self-selected speed and as fast as possible following an auditory cue. Root mean square amplitude of the APAs and speed of task performance (raise time) was calculated. Mixed model ANOVA were used to test for main effects of task (5 levels, SLR, ULR SLOW and FAST pre-fatigue, ULR SLOW and FAST post-fatigue) and group and task*group interactions. Results Raise time was faster for the ULR FAST than the ULR SLOW. Raise time did not differ between groups and remained the same post-fatigue. For all muscles, APA amplitude increased with task difficulty and with task speed. For right and left EO there was a significant task*group interaction. For both muscles, amplitude of activity increased for ULR FAST pre-fatigue, but this speed-dependent increase in amplitude did not occur in the LBP group post-fatigue. Conclusion Central modulation of APAs in non-fatigued muscles occurs in response to fatiguing exercise. This likely facilitates maintenance of postural stability and task performance. The ability to modulate abdominal muscle APAs in response to fatigue and task demands is impaired in young adults with a history of LBP even during symptom remission.
Soliman, Jolene Kay and Smith, Jo Armour, "Central Modulation of Postural Control in Response to Task Demands and Fatigue in Individuals with and without a History of Low Back Pain" (2023). Student Scholar Symposium Abstracts and Posters. 571.