Strength and endurance of the lumbar extensor muscles and their predictors: A cross-sectional study in healthy subjects

The purpose of this cross-sectional study was to present the values of maximal isometric lumbar extensor muscle strength (MILEMS) and lumbar extensor muscle endurance (LEME) in healthy subjects and to study the influence of physiological factors on these parameters. MILEMS using a hand-held dynamometer in three positions (prone, sitting, standing) and LEME using the Biering-Sørensen test were assessed in 115 healthy volunteers. The MILEMS measurements for the specific positions were correlated with each other (Pearson correlation coefficients 0.31-0.87, p < 0.001). In univariable linear regression, sex showed the highest effect on MILEMS prediction in sitting position (higher strength in men, P < 0.001, R² of 20.4 %). Multivariable linear regression led to construction of a calculator to estimate predicted MILEMS in the sitting position in relation to sex, age and BMI with R² of 32.2 %. LEME was mostly predicted by BMI (decrease of LEME with increasing BMI, P < 0.001), but multivariable regression analysis did not allow the construction of a reliable calculator to predict this parameter. In conclusion, we provided values for MILEMS and LEME. A calculator was developed to predict MILEMS and to determine the percentile of measured MILEMS in an individual. It is expected to be particularly useful in assessing patients who are likely to have lumbar extensor muscle impairment.