title: Trunk muscle reactions to sudden unexpected and expected perturbations in the absence of upright postural demand.
abstract: The aim was to increase the understanding of the multifunctional role of the trunk muscles in spine control, particularly transversus abdominis (TrA). In 11 healthy males, intramuscular fine-wire electromyography (EMG) was obtained bilaterally from TrA, obliquus externus (OE), rectus abdominis (RA) and erector spinae (ES). The subjects lay on their right side on a horizontal swivel-table with immobilized pelvis and lower limbs and the trunk strapped to a movable platform. Unexpected or expected release of loads attached to the table by steel cables produced a perturbation inducing either trunk flexion or extension. The timing and the amplitude of activation of TrA were independent of direction of induced trunk movement. Furthermore, timing of TrA activation was simultaneous to or later than that of the more superficial abdominal muscles. Expectation of the perturbation caused a general shortening of onset latencies. The results indicate a direction independent function of TrA in lumbar spine control. Balancing the trunk vertically appears to add specific demands, since the recruitment of TrA in relation to the other abdominal muscles differed from earlier experiments in standing.
authors.affiliation: School of Health and Medical Sciences, Family Medicine Research Centre, Orebro University, Box 1613, 701 16, Orebro, Sweden. martin.eriksson-crommert@orebroll.se
authors.forename: A E Martin
authors.initials: AE
authors.lastname: Eriksson Crommert
authors.forename: Alf
authors.initials: A
authors.lastname: Thorstensson
mesh_terms: D000009:Abdominal Muscles / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D004576:Electromyography / Q000379:methods; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult