This is very difficult to objectivize in phy­sical terms because it is not usual'y possible to gauge the forces against which certain muscles have to react by resorting to continuous contraction. ###>Cette in­tensité est extrêmement difficile à objectiver physiquement car il n'est généralement pas possible d'évaluer les forces auxquelles certains muscles doivent opposer une force contraire par une contraction continue.