1. Biomechanics and Motor Control, University of Münster, Horstmarer Landweg 62b, 48149 Münster, Germany
2. Department of Mathematics, Mantell Building, University of Sussex, Falmer, Brighton, BN1 9RF, UK
3. Biomechanics Group, Institute of Sport Science, Friedrich-Schiller-University Jena, Seidelstr. 20, D-07749 Jena, Germany