Agreement Between Handheld and Fixed Dynamometry for Hip Strength Assessment in Young Soccer Players and Non-Soccer Controls: An Exploratory Study

Background/Objectives: Handheld dynamometers are increasingly used for muscle strength assessment because of their low cost, portability, and ease of implementation in clinical and sports settings. However, it remains unclear whether measurements obtained using handheld and externally fixed dynamometers can be used interchangeably in young soccer players. This exploratory cross-sectional study compared measurements of hip adductor and abductor strength obtained using a handheld dynamometer (DynaMo) and an externally fixed dynamometer (ForceFrame) in young soccer players and non-soccer controls. Methods: Forty healthy men (20 U-21 soccer players and 20 non-soccer controls) were included. Isometric hip adduction and abduction strength were assessed bilaterally using DynaMo and ForceFrame during a single testing session. Agreement between measurement methods was evaluated using Bland–Altman analysis, and associations between methods were determined using Spearman’s rank correlation coefficients. Results: Moderate to very strong positive correlations were observed between DynaMo and ForceFrame measurements (r = 0.44–0.96), although the correlation for left hip abduction in soccer players did not reach statistical significance (p = 0.052). Nevertheless, Bland–Altman analysis revealed a systematic bias, with ForceFrame producing higher normalized hip strength values than DynaMo across all assessments. The mean bias ranged from 2.02 to 3.34 N/kg (95% LoA 0.21 to 4.83 N/kg) in the soccer group, and 0.92 to 2.00 N/kg (95% LoA 0.18 to 2.93 N/kg) in the non-soccer group. Conclusions: Although moderate to very strong correlations were observed between the two dynamometry systems, systematic differences in recorded strength values indicate that the two systems may not be considered directly interchangeable for assessing hip abductor and adductor strength. For longitudinal monitoring and clinical decision-making, repeated assessments should preferably be performed using the same measurement system, and caution is warranted when interpreting absolute hip muscle strength values. Given the exploratory design and relatively small sample, these findings should be interpreted cautiously and confirmed in larger studies.