Introduction 1954 1996 1995 2003 2001 2001 2004 2003 2003 2003 1997 2003 2001 1993 2004 2003 2003 1997 2005 2006 2005 2001 1999 1994 2005 2006 1999 1981 2001 1993 1986 2004 2004 1999 1999 2000 1982 1983 2000 Methods Subjects Seven healthy male subjects (23–32 year, 69–83 kg, and 1.73–1.93 m) volunteered to be subjects for this investigation. Before participation, each subject was thoroughly informed about the procedures and provided written informed consent prior to testing. Only subjects capable of >95%VA across knee angles (see below) were included in the present study. The study was performed according to the Declaration of Helsinki and approved by the local ethics committee. Subjects did not perform any fatiguing exercise 48 h prior to measurements. Experimental procedures 2004 2005 Torque measurements 2005 −4  Electrical stimulation Discussion 2005 Discussion Voluntary activation 1 1995 2001 2006 2001 2005 2005 2003 1992 2003 2003 \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{VA(}}\% {\text{) = }}100\, - \,{\text{[(triplet torque increment}}\,{\text{/}}\,{\text{resting triplet)}}\, \times \,{\text{100}}] $$\end{document} Fig. 1 vertical arrows vertical dashed lines  1 2001 2003 1993 2004 2003 2003 1997 2 3 2001 1994 2003 1997 R 2 3 Fig. 2 empty circles black triangles dashed and solid lines dotted lines R 2  Fig. 3 a y x open circles filled triangles dashed and solid lines dotted lines b x open circles filled triangles linear regression line R 2  Surface electromyography 2 Statistics P Results R 2 3 4 Fig. 4 black triangles solid line white squares dashed line grey circles dotted line  P 1 P 1 1 Table 1 Torque  Knee angle 30° 60° 90° ICC MVC (Nm) 186.1 ± 36.6 278.4 ± 44.5* 189.6 ± 19.7 0.99*** Triplet torque (Nm) 65.9 ± 10.0** 91.6 ± 15.8 80.1 ± 10.8 0.96*** n P P *** Significant ICC, the intraclass correlation coefficient (ICC) was calculated for the measurements made on experimental days 1 and 2 and is shown in the last column Voluntary activation 5 P 6 Fig. 5 black triangles white squares grey circles horizontal dotted line  Fig. 6 grey squares open circles 5  EMG P 7 7 7 7 7 Fig. 7 a black triangles white squares grey circles P 1 2 2 b white circles black circles black circles  7 7 Discussion In the present study, the relationship between calculated VA and voluntary torque was assessed in subjects with high ability for maximal VA at different knee angles. At the same time, the EMG–torque relationship in these selected subjects was examined. The first and main finding of the present study was that when VA is calculated to be ∼90% (as in regular healthy subjects), this probably represents a considerable overestimation of the subjects’ ability to maximally drive their quadriceps muscles. An additional finding was that, although resting triplet torque was lower at 30° versus 90°, this was of minor influence on the calculated maximal VA in our subjects. Furthermore, a relatively large increase in normalized rsEMG was observed as MVC was approached, making the shape of the normalized EMG–torque relationship of the knee extensors curvilinear. Maximal voluntary activation and knee angle 5 2001 2003 1993 2004 2003 2003 1997 1986 1986 1994 1988 2001 1 1997 2004 2+ 2+  2001 1 2 3 1997 2004 1997 2003 2003 2001 Calculated voluntary activation in relation to relative voluntary torque 1996 2001 2003 1993 2004 2003 2003 1997 3 3 5 6 Experimental and methodological factors 1996 1999 1997 1999 8 2005 2004 2003 1993 Fig. 8 upper panel lower panel left panel top right lower right  The EMG–torque relationship 7 1983 2000 2000 1993 1999 1999 2001 1999 1993 1997 7 EMG, superimposed torque and voluntary activation 1999 7 1999 1999 2004 How can we be certain that our selected subjects did indeed approach their true MTC? The only way to truly determine the MTC of a muscle is by the use of tetanic nerve stimulation. In two subjects with exceptional ability for maximal VA (>99%), supramaximal tetanic nerve stimulation (2 s, at 150 Hz) of the knee extensors was performed and torque levels showed no further increase above MVC (data not presented). Applying supramaximal tetanic nerve stimulation is not recommended, however, as it is highly unpleasant and could be harmful to certain vulnerable subject groups (e.g. subjects with an ACL deficiency). 1995 2003 2001 1996 2001 2004 1992 2003 2003 1997 1999 2006 2000 In conclusion, when maximal VA is calculated to be ∼90% (as in regular healthy subjects), this probably represents a considerable overestimation of the subjects’ ability to maximally drive their quadriceps muscles. Moreover, the effect that the length dependent size of the resting triplet has on the calculation of VA with the conventional method is only minimal when VA is greater than 95%. Furthermore, a curvilinear shape of the EMG–force relationship may be caused by a disproportionately large increase in normalized rsEMG when MVC is approached in subjects with very high capacity to drive their muscles maximally.