# Reliability of a New Portable Dynamometer for Assessing Hip and Lower Limb Strength
## 4 Discussion
Results are similar despite the following differences in body positions and lever arm lengths: HFLX was measured in 90\({}^{\circ}\) hip flexion with short lever arm compared to our measurement of HFLX in neutral position with long lever arm; HEXT in prone position in 4-point support and 90\({}^{\circ}\) knee flexion with short lever arm compared to prone lying position with neutral knee position and with long lever arm; HADD and HABD in supine position with 45\({}^{\circ}\) knee and hip flexion with short lever arm compared to supine position and neutral position in hip and knee joint with long lever arm; and HIR and HER in supine position with hip and knee in 90\({}^{\circ}\) flexion compared to prone position in 4-point support. Furthermore, [PERSON] et al. (2018) [14] found similar low within-individual variation (CV < 10%) and excellent reliability using the GroinBar device for bilateral HADD peak force compared with results from our study. In addition, hip strength measurements using hand-held dynamometry displayed comparable (moderate to excellent) reliability [25, 26, 27]. Based on the abovementioned findings, it can be concluded that the externally fixated dynamometer MuscleBoard(r) analyzed in our study could be a reliable alternative for assessing hip and lower limb strength compared to hand-held dynamometry, as it is not dependent on examiner's strength. Additionally, handling this dynamometer requires less knowledge and experience compared to hand-held dynamometry. When measuring HADD, HABD, HIR, and HER, bilateral contractions had systematically better (good to excellent) intra- and inter-session test-retest reliability compared with unilateral contractions. There could be two main reasons that made maximal voluntary isometric contractions (more) difficult to perform during unilateral contractions: (i) lack of stabilization/fixation of body position and (ii) participants' division of attention. Participants were instructed to abduct or rotate the non-measured leg outside of sensor braces and to maintain this position during unilateral measurements in addition to generating maximal isometric torque with the measured leg. This seemed even more difficult during unilateral abduction and adduction in the supine position, as the peak torque generated with the measured leg was partly dependent on strong fixation of the trunk, upper body, and non-measured leg. Thus, in our case, participants resisted with the non-measured leg at the outer edge of the dynamometer to improve stabilization during unilateral adduction. During unilateral abduction, participants tried to stabilize themselves by pushing the non-measured leg into the ground, which occasionally caused a slight movement of the dynamometer in the direction of abduction of the measured leg. To prevent this movement, the examiner had to provide additional external stabilization (by holding the dynamometer in place). Moreover, the absence of bilateral deficit (reduction of the produced force from a single leg during maximal bilateral contraction) could be explained by the same two factors (lack of body position stabilization/fixation and division of attention during unilateral measurements). The sum of peak torques for the unilaterally measured left and right leg was lower than peak torques for the bilaterally measured test in all three sessions (e.g., for the adduction in the first session: 2.09 Nm/kg for bilateral test, >0.77 Nm/kg for the right leg, + 0.77 Nm/kg for the left leg). To our knowledge, this is the first study in which both the reliability of bilateral and unilateral contractions was tested on this type of externally fixated dynamometer. It would be interesting to see if the participants would achieve comparable results in terms of bilateral deficit on similarly designed dynamometers (e.g., GroinBar device). An advantage of the MuscleBoard(r) compared to other recently introduced portable, externally fixed dynamometers, is its ability to measure the strength of knee extensors and plantarlexors.