The aim of the study was to examine the intra-observer reliability and criterion validity of the Back
Check® linear dynamometer (model 607; Dr. Wolff®, Sports & Prevention GmbH, Arnsberg,
Germany) against the gold standard Biodex® isokinetic dynamometer (Model 2000, System 4 Pro;
BiodexCorporation, Shirley, NY, USA) for the measurement of peak torque of trunk flexors and
extensors under isometric conditions. The study included 43 individuals (25 women and 18 men).
Participants performed three measurements in random order during the same visit, two on the
linear dynamometer (in the sitting and standing positions) and one on the rotator dynamometer.
The highest value of the three measurements was used for analysis.
Intra-observer reliability was assessed using the intraclass correlation coefficient (ICC) and the
coefficient of variance (CV). Criterion validity was calculated using a paired t-test for dependent
samples (Wilcoxon rank test where the assumption of normal distribution of differences was not
met, normality of distribution was checked with the Shapiro-Wilk test) and Bland-Altman
analysis.
The results showed statistically significant differences between measurements with the Biodex
dynamometer in all tests except the trunk flexion test on the Back Check® sitting dynamometer
(p=0.32). Bland-Altman analysis showed the highest agreement in the same test.
Based on this, we can conclude that the measurements of maximum trunk torque on the linear
dynamometer have the highest agreement with the gold standard in measuring trunk flexion in
sitting. The other measurements showed, despite good repeatability, systematic differences that
make it impossible to use both devices interchangeably.
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