Muscle activation during stride: Presentation of time normalized grand averaged amplitude curves of left multifidus muscle and the pooled activity of all investigated back muscles in polar diagrams: ipsilateral heel strike occurs at noon, relative stride time proceeds clockwise. The black circle represents ipsilateral, the grey circle contralateral stance phases. Control shoes ¼ black, optimal cushioned test shoes ¼ grey. Please note the reduced and counter clockwise shifted amplitude peak while wearing the test shoes with optimal cushioning