A new reliable device to assess trunk extensors strength

Purpose: This study aimed to examine the reliability of trunk extensor strength assessment with a functional electromechanical dynamometer (FEMD). Methods: Thirty-one men performed strength assessment at different velocities (V) (V₁ = 0.15 m·s⁻¹, V₂ = 0.30 m·s⁻¹, V₃ = 0.45 m·s⁻¹) and range of movement (R) (R₁ = 25% cm; R₂ = 50% cm), and isometric contraction at 90º. Reliability was obtained through the intraclass correlation coefficient (ICC), typical error (TE), and coefficient of variation (CV). Results: The absolute reliability provided stable repeatability of the average eccentric strength in the V₁R₁ condition (CV = 9.52%) and the maximum eccentric strength in V₁R₁ (CV = 9.63%) and V₂R₂ (CV = 9.66%). The relative reliability of the trunk extensor’s average strength was good (ICC = 0.77–0.83) for concentric and good (ICC = 0.78–0.85) and moderate (ICC = 0.67–0.74) for eccentric contraction. Also, good (ICC = 0.77–0.81) and moderate (ICC = 0.55–0.74) reliability of the maximum strength were obtained for concentric and eccentric contraction. The most reliable manifestation to evaluate the concentric (CV = 11.33%) and eccentric (CV = 9.52%) strength was the average strength in the V₁R₁ condition and the maximum strength (CV = 10.29%) to isometric assessment. The average concentric strength in the V₂R₂ condition (r = 0.69) and the maximum eccentric strength in the V₁R₁ condition (r = 0.65) were the best related to the maximum isometric strength. Conclusions: FEMD is a highly reliable device to evaluate trunk extensors strength.