Differences in the muscle activity patterns of trunk extensors based on active straight leg raising test scores: a pilot study

Abstract

The purpose of this pilot study was to investigate the minimum sample size required to determine whether the muscle activity patterns of the superficial trunk extensor muscles differ among individuals when distinct active straight leg raise (ASLR) test scores are measured using a functional movement screening (FMS) system. Eighteen and nine individuals with FMS–ASLR test scores of 1 (with dysfunction) and 3 (without dysfunction), respectively, were included in the analysis. None of the participants had back or leg pain. For the right ASLR test, we calculated the differences in muscle activity delay among the right and left longissimus thoracis, right and left iliocostalis lumborum, and right and left multifidus muscles in relation to the onset of muscle activity in the right rectus femoris muscle. We also calculated the effect size (Hedges’ g) and the required sample size at α = 0.05 and β = 0.2. Our results demonstrate that the group with an FMS-ASLR test score of 1 had a shorter delay in the muscle activities of the right and left longissimus thoracis, right and left iliocostalis lumborum, and right and left multifidus muscles relative to the right rectus femoris muscle than the group with an FMS–ASLR test score of 3. Analysis revealed that the study required a sample size of at least 28 participants (14 with an FMS–ASLR test score of 1 and 14 with an FMS–ASLR test score of 3).