Abstract Purpose The aim of this study was to evaluate whether unilateral and bilateral assessments display comparable results during the isometric long-lever bridge and to examine the directionality of asymmetry fluctuations across testing occasions. Methods Forty-four participants comprising of 30 men (age: 19.4 ± 1.3 years; height: 179.8 ± 6.3 cm; body mass: 80.4 ± 10.3 kg) and 14 women (age: 20.0 ± 1.3 years; height: 166.9 ± 7.2 cm; body mass: 64.4 ± 7.4 kg) volunteered to participate in the study. All participants completed two separate testing sessions consisting of two maximal bilateral and unilateral repetitions respectively of the isometric long-lever bridge performed at a knee angle of 30° degrees. All data were analyzed to assess the limb symmetry index (LSI) between testing procedures at 50-, 100-, 150-, 200-, 250 ms and at peak force (N). Results Large differences in variance were observed within and between unilateral and bilateral tasks, particularly for rapid force and peak force asymmetry measures, as revealed by principal component analysis. Fair to slight agreement was observed between unilateral and bilateral assessment methods ( k = 0.05 – 0.24) and large to very large relationships were observed between early force (≤ 100 ms) and late force (150-, 200- and 250 ms) within the same assessment category. Conclusions These findings suggest that asymmetries assessed bilaterally do not carry over well to asymmetries assessed unilaterally, therefore displaying poor convergent validity. Furthermore, rapid asymmetry measures (asymmetries within 250 ms) and peak asymmetry measures (maximum during the trial) appear to demonstrate differing constructs.
Sundh et al. (2026) studied this question.