Assessment of Lumbar Extensor Muscles in the Context of Trunk Function, a Pilot Study in Healthy Individuals

A comprehensive assessment of trunk function, including the lumbar extensor muscles, appears to be important in various conditions affecting axial musculature. This pilot cross-sectional observational study aimed to define a battery of tests that comprehensively assess trunk muscle function (strength and muscular endurance). Sixty subjects without low back pain (LBP) underwent measurement of isometric lower back extensor strength using a hand-held dynamometer (HHD) in three positions; measurement of respiratory muscle strength; and Biering–Sørensen, prone-plank, and side-bridge tests. The repeatability, short-term and long-term reliability using the HHD device in different postural positions was confirmed. The greatest isometric lower back extensor strength was generated in the sitting position by male subjects. Time of effort in the Biering–Sørensen test was longer in women and older subgroups than in men and younger individuals, although this was not the case for the other two muscular endurance tests. This pilot monitoring of trunk muscle strength and endurance in healthy volunteers may lead to a better understanding of trunk muscle function. Based on this methodological background, the authors aim to use the defined battery of tests in their further studies in a group of patients with LBP and certain neuromuscular diseases to verify its usefulness in clinical practice.

Reliability and validity of three isometric back extensor strength assessments with different test postures

Objective To compare the test-retest reliability and validity of three simple maximal isometric back extensor strength (BES) assessment protocols with different test postures, and to recommend an optimal clinical protocol to quantify BES. Methods Asymptomatic adults, aged over 45 years, were assessed for maximal isometric BES using external fixation of dynamometers, with the subject in standing, prone and sitting positions, respectively. Measurements were repeated at a one-week interval to examine test-retest reliability. Validation was performed by comparing with results obtained from isokinetic dynamometer assessments. Results Out of a total of 60 included participants, intra-class correlation coefficients (ICC) were 0.92, 0.93 and 0.90 in standing, prone and sitting positions, respectively. Correlation analyses revealed acceptable convergent validity in the standing and prone position (r = 0.50 and 0.54, respectively), whereas tests conducted in the sitting position showed a relatively low validity (r = 0.32). Among the three protocols, measurement error was lowest in the prone position. Conclusions Maximal isometric BES assessment in the prone position was shown to be the most reliable and valid protocol, and may be considered the preferred option for assessing BES in clinical practice.