Reliability and agreement of a novel trunk extension strength assessment device and association to dynamic performance.

BackgroundTrunk extension strength (TES) has been identified as a modifiable risk factor for low back pain, yet measurement solutions that are reliable, accessible, and designed specifically for TES are lacking. Insights between isometric and isokinetic TES metrics are also limited.ObjectiveTo assess the intersession measurement reliability and agreement between a new custom-designed TES dynamometer (CTD) and modified fixed dynamometer (MFD) system, and the relationship between isometric and isokinetic TES.MethodsThe study contained 30 healthy young adult individuals (18F/12 M, 24.4 ± 2.8 yrs, 1.70 ± 0.08 m, 75.1 ± 18.5 kg), respectively. Maximal isometric TES was measured on both dynamometers during two within-day sessions, 15 min apart. Eccentric (E) and concentric (C) isokinetic TES were also measured at 30 and 120 deg/s.ResultsRelative reliability was good to excellent for isometric measurements and excellent across all isokinetic tests. Absolute reliability metrics were higher for the CTD than the MFD, but comparable to other similar devices reported in the literature. Relative agreement between the dynamometers was moderate, while significant mean bias was detected (MFD < CTD). The relationships between isometric and isokinetic TES were small to moderate for the CTD and moderate to large for the MFD.ConclusionThis work presents a new device and approach to TES measurement that are reliable and accessible, along with new insights on how isometric TES relates to dynamic muscle performance. Whether isometric or isokinetic TES provides clinicians with predictive or prognostic insight requires further research.