Body mass normalization for isometric tests of muscle endurance

The primary purpose of this study was to derive allometric parameters for normalizing Biering-Sorensen and Plank Test scores (measures of isometric back and abdominal muscle endurance, respectively) to body mass. The secondary purpose was to determine if allometric scaling with derived allometric parameters or the theoretical allometric parameter (b = -0.33) is the more appropriate method for normalizing Biering-Sorensen and Plank Test scores to body mass. A sample of 83 male career firefighters (age = 35.7 ± 9.4 years; body mass = 89.5 ± 14.8 kg) participated in this study. Significant correlations were found between body mass and test scores (Biering-Sorensen Test: r = -0.36, p = 0.001; Plank Test: r = -0.55, p < 0.001). Derived allometric parameters for Biering-Sorensen and Plank Tests were b = -0.932 and -1.369, respectively. Allometric scaling with the derived allometric parameters was deemed appropriate at normalizing Biering-Sorensen and Plank Test scores because it caused the correlations between body mass and test scores to become insignificant (Biering-Sorensen Test: r = 0.10, p = 0.354; Plank Test: r = 0.14, p = 0.173). Allometric scaling with the theoretical allometric parameter was deemed inappropriate for normalizing Biering-Sorensen and Plank Test scores because it was not robust enough to get rid of the significant correlations between body mass and test scores (Biering-Sorensen Test: r = -0.23, p = 0.034; Plank Test: r = -0.43, p < 0.001). Allometric scaling with derived allometric parameters should be used to normalize Biering-Sorensen and Plank Test scores to body mass, particularly when attempting to account for changes in body mass across time intervals and differences in body mass across individuals.