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. Katz and Shadwick (2000) argued that this error leads to inaccurate determination of the phase of EMG activity relative to peak muscle length. Further, they suggest that phase does not vary along the length of the animal. Instead, the electrical and mechanical waves travel down the body of a swimming fish at the same rate (Katz and Shadwick 2000).This would have an important impact on patterns of power production (discussed below). Katz and Shadwick’s assertions might be true for a few species (e.g. skipjack tuna). However, there are at least three lines of evidence that the problem, as they describe it, is of limited interest. First, many datasets on muscle length change were not collected with a reliance on lateral displacement but accurately determine muscle length change and thereby, muscle phase via local backbone curvature (e.g. Jayne and Lauder 1995a;Gillis 1998). Second, recent work using sonomicrometry
has clearly shown that differences in the electrical and mechanical wave speeds are, at the least, common
(e.g. Coughlin and Rome1996a; Hammond et al. 1998; Coughlin 2000). Lastly, some datasets called into question by Katz’s theoretical work (e.g.work on saithe and mackerel, Wardle and Videler1993) have been recently verified as accurate using sonomicrometry (J. Altringham, personal communication).