Purpose While motor unit recruitment may be impaired for some clinical populations, and while all-out testing procedures involve repeated maximal contractions to accurately estimate critical torque (CT), no previous study has precisely examined the relationships between voluntary activation percentage (VA%) and difference in CT estimation according to common methods. The aim of the current study was to investigate whether the VA% influences the CT estimated according to the two reference methods.  Methods CT was estimated in 68 participants who completed a 5-min all-out test involving plantar flexors (PF; <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">$n=38$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>=</mo> <mn>38</mn> </mrow> </math></EquationSource> </InlineEquation>) or knee extensors (KE; <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">$n=30$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>=</mo> <mn>30</mn> </mrow> </math></EquationSource> </InlineEquation>), using both the exponential method (i.e., the exponential regression asymptote [CTexp]) and the end-test method (i.e., the average of last 6 torque peaks [CTend-test]). For both muscle groups, participants performed 60 maximal isometric contractions (3 s of contractions/2 s of rest) and VA% was estimated before, after every six contractions and after the all-out test. Results The major findings were that the lower the baseline VA%, the higher the difference in CT estimations between both methods (<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="133" /> </InlineMediaObject> <EquationSource Format="TEX">${r}^{2}=0.43 ; p<0.01$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>r</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.43</mn> <mo>;</mo> <mi>p</mi> <mo><</mo> <mn>0.01</mn> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="133" /> </InlineMediaObject> <EquationSource Format="TEX">${r}^{2}=0.31; p<0.01$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>r</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.31</mn> <mo>;</mo> <mi>p</mi> <mo><</mo> <mn>0.01</mn> </mrow> </math></EquationSource> </InlineEquation> in PF and KE, respectively) and that CTexp was lower than CTend-test (<InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq5.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="TEX">$p<0.001$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo><</mo> <mn>0.001</mn> </mrow> </math></EquationSource> </InlineEquation> for both), in both muscle groups. Moreover, results showed that the higher the curvature constant from the exponential regression (i.e., the slower the fatigue development), the higher the difference in CT estimation (<InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="141" /> </InlineMediaObject> <EquationSource Format="TEX">${r}^{2}=0.43 ; p<0.001$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>r</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.43</mn> <mo>;</mo> <mi>p</mi> <mo><</mo> <mn>0.001</mn> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11332_2025_1382_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="141" /> </InlineMediaObject> <EquationSource Format="TEX">${r}^{2}=0.53; p<0.001$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi>r</mi> </mrow> <mn>2</mn> </msup> <mo>=</mo> <mn>0.53</mn> <mo>;</mo> <mi>p</mi> <mo><</mo> <mn>0.001</mn> </mrow> </math></EquationSource> </InlineEquation> in PF and KE, respectively). Conclusion The current study demonstrates the inconsistency between two common CT estimation methods and shows that the differences are linked to the ability to produce maximal voluntary contractions. While CT is an important parameter for quantifying neuromuscular fatiguability in clinical populations, the all-out test is limited in its current form. We suggest new ways for estimating CT that rely less heavily on VA% capacity, which would therefore be more adapted to participants subject to neuromuscular deconditioning.

Associations between voluntary activation and difference in critical torque estimation between common methods in untrained participants

期刊论文
发表日期：

2025年4月1日

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Antonin Le Corre,
Nicolas A. Turpin,
Jérémie Begue,
Florian Chouchou,
Antoine Mariani,
Nathan Caron,
Georges Dalleau

摘要

Purpose

While motor unit recruitment may be impaired for some clinical populations, and while all-out testing procedures involve repeated maximal contractions to accurately estimate critical torque (CT), no previous study has precisely examined the relationships between voluntary activation percentage (VA_%) and difference in CT estimation according to common methods. The aim of the current study was to investigate whether the VA_% influences the CT estimated according to the two reference methods.

Methods

CT was estimated in 68 participants who completed a 5-min all-out test involving plantar flexors (PF; $n=38$ $n = 38$ ) or knee extensors (KE; $n=30$ $n = 30$ ), using both the exponential method (i.e., the exponential regression asymptote [CT_exp]) and the end-test method (i.e., the average of last 6 torque peaks [CT_end-test]). For both muscle groups, participants performed 60 maximal isometric contractions (3 s of contractions/2 s of rest) and VA_% was estimated before, after every six contractions and after the all-out test.

Results

The major findings were that the lower the baseline VA_%, the higher the difference in CT estimations between both methods ( ${r}^{2}=0.43 ; p<0.01$ $r^{2} = 0.43; p < 0.01$ and ${r}^{2}=0.31; p<0.01$ $r^{2} = 0.31; p < 0.01$ in PF and KE, respectively) and that CT_exp was lower than CT_end-test ( $p<0.001$ $p < 0.001$ for both), in both muscle groups. Moreover, results showed that the higher the curvature constant from the exponential regression (i.e., the slower the fatigue development), the higher the difference in CT estimation ( ${r}^{2}=0.43 ; p<0.001$ $r^{2} = 0.43; p < 0.001$ and ${r}^{2}=0.53; p<0.001$ $r^{2} = 0.53; p < 0.001$ in PF and KE, respectively).

Conclusion

The current study demonstrates the inconsistency between two common CT estimation methods and shows that the differences are linked to the ability to produce maximal voluntary contractions. While CT is an important parameter for quantifying neuromuscular fatiguability in clinical populations, the all-out test is limited in its current form. We suggest new ways for estimating CT that rely less heavily on VA_% capacity, which would therefore be more adapted to participants subject to neuromuscular deconditioning.