The accuracy of measurements of muscle length change, particularly with regard to the timing of peak length, has been called into question (Katz and Shadwick 1998, 2000).Katz and Shadwick suggest that a number of studies have miscalculated muscle length change because lateral displacement of the body, instead of body curvature, was used as an indicator of muscle length. Since lateral displacement and backbone curvature are out of phase (Jayne and Lauder1995b), such reliance would lead to error