Interindividual variability of isometric endurance with regard to the endurance performance limit for static work.

In literature there are doubts concerning the 15% MVC (maximal voluntary contraction) level and invariability of isometric endurance, as described by ROHMERT (1962) as a "biologische Konstante". Therefore, 3 experimental sets using different levels of relative loads from approximately 2.9% (individual weight of forearm) to 50% MVC and different holding times (up to 1 hr) were performed concerning elbow flexion and knee extension. Measurements of the times until exhaustion and muscular fatigue (EMG) underlined the great variability of the holding times and showed that the mean endurance performance limit for isometric exercise lies neither at the 15% MVC level nor can it be used as a "biologische Konstante". The muscle fibre composition is discussed as the main reason for the observed variability.