Cyclic upper body perturbations caused by a flexible pole: Influence of oscillation frequency and direction on trunk muscle co-ordination

Abstract

Objective: The effect of a newly developed training device on trunk muscle co-ordination patterns was investigated. Design: A cross sectional survey of 30 healthy volunteers was executed. The task was to maintain position and motion of a flexible pole that was set into oscillation. Oscillations were applied at three frequencies (3, 3.5, 4.5 Hz), in horizontal and vertical directions. SEMG signals of five trunk muscles were measured. Co-ordination was assessed by calculating mean relative amplitudes and mean, as well as, grand averaged muscle ratios during oscillation cycle for front over back (F/B), internal over external oblique (OI/OE), and multifidus over erector spinae (MF/ES) muscles. Results: Vertical oscillation evoked increased mean MF relative amplitudes and mean F/B and MF/ES muscle ratios in comparison with horizontal oscillation. Grand averaged F/B ratio was phase shifted about 180 ◦ of relative cycle between both oscillation directions. With increasing oscillation frequency mean F/B ratio increased, but OI/OE ratio decreased. Amplitude range of grand averaged muscle ratios during oscillation cycle was augmented with increasing frequency. Conclusions: The gathered normative data can serve as an initial data basis for further investigations on low back pain patients. Relative to oscillation direction and frequency, demands on trunk muscles vary from primarily stabilizing towards mobilizing activities.