Repeatability of the Mean Power Frequency of the Endurance Level During Fatiguing Isometric Muscle Contractions

A criteria to decide whether the sustained isometric contraction was long enough for reliable determination of the so called "endurance level" (MNFp) were tested. It was shown that if the maximal voluntary muscle contraction is sustained for long enough so that the fitted exponential curve fulfills certain predefined derivative criteria as described in the text, the data could be used for reliable estimation of the MNFp without the experimental MNF data actually reaching the plateau level. Using these criteria it was found that the difference in MNFp values of the two consecutive series of maximal voluntary isometric muscle contractions were not statistically significant.