Fig. 7. Contraction force (% max. voluntary contraction; MVC) at which the initial intensity peak occurred during each graded contraction as a function of the center frequency for each wavelet domain. Rectus femoris, open triangles; vastus lateralis, solid diamonds; vastus medialis, open diamonds; lateral gastrocnemius, solid circles; medial gastrocnemius, open circles; soleus, open squares. Values are the mean ± S.E.M. (30N50 for f_c<250 Hz and 6N50 for 250f_c400 Hz). The third order polynomial regression lines (Table 3; P<0.001) were calculated from the mean points for each muscle and for 1k13 (19f_c542 Hz).