Activation characteristics of trunk muscles during cyclic upper-body perturbations caused by an oscillating pole

Objective: To evaluate the effect of a new device on trunk muscle activation. Design: Cross-sectional survey of trunk muscle activation characteristics. Setting: Physiologic laboratory at university institute. Participants: Thirty healthy subjects (15 men, 15 women) were recruited from a university campus. Interventions: A simple flexible pole that applies rapidly alternating forces on the trunk when set into motion was used. The device was held horizontally in both hands, in front of the body. It was used at 3 different oscillation frequencies (3, 3.5, 4.5Hz), in horizontal and vertical plane, respectively. Main Outcome Measures: Surface electromyography of 5 trunk muscles was measured and the data were normalized according to relative cycle time. Time dependent (amplitude curve) and time independent (mean amplitude over cycle) parameters were used for analysis. Results: Rectus abdominis and external oblique muscle amplitudes were directly proportional with oscillation frequency (analysis of variance), and these effects were independent of sex. Multifidus amplitude levels were subject to oscillation plane with increased levels for vertical oscillation in men but not in the women. All abdominal muscles exhibited continuous activation pattern, independent of oscillation plane. Back muscles changed from a continuous activation in horizontal plane into similarly phasic patterns in vertical oscillation plane. The occurring amplitude peak moved forward in relative cycle with increasing oscillation frequency. Conclusions: Back muscle activation patterns were subject to oscillation plane. Abdominal muscle activation was independent from oscillation frequency and oscillation plane. These normative data may be used to identify disturbed trunk muscle coordination patterns and to control success of functional restoration during rehabilitation interventions of back pain patients.