Muscle stability deficits are strongly associated with musculoskeletal complaints in football (soccer) players: Adaptive Force ratio outperforms conventional strength parameters—a cross-sectional study with preliminary follow-up
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Introduction
Given the documented limitations of strength-based screening, novel approaches are warranted. Adaptive Force (AF)—being closer to injury-prone movements than conventional strength assessments—offers an alternative. This study examined the association between AF-based muscle stability and musculoskeletal complaints in football players and compared AF-derived and conventional strength parameters in their discriminative capacity, complemented by a preliminary prospective follow-up.
Methods
AF and maximal voluntary isometric contraction (MVIC) were measured in 23 male football players across five bilateral muscle groups (knee extensors/flexors; hip flexors/adductors/abductors). AF parameters (maximal isometric AF, maximal AF, AF-Ratio), MVIC and hamstrings-to-quadriceps (H:Q) ratio were compared between players with and without complaints assessed via questionnaire at baseline and six-month follow-up (n = 13).
Results
Stability deficits were strongly associated with complaints (OR = 54.0, 82% side concordance). AF-Ratio discriminated clearly between players with and without complaints ( d = −1.47, AUC = 0.93), strongest for hip abductors ( d = −1.64). Players with follow-up complaints showed lower baseline AF-Ratio ( d = −1.45, AUC = 0.86) and more stability deficits ( d = 1.67). MVIC and H:Q ratio discriminated in neither analysis ( p > 0.500, AUC ≤ 0.44); AF-Ratio significantly outperformed both in discriminative capacity at baseline ( p ≤ 0.002) and follow-up ( p ≤ 0.028).
Conclusion
The findings suggest that muscle stability assessment outperforms conventional strength parameters in discriminating players with and without complaints, with preliminary follow-up data providing tentative support for predictive value. The concept of functional instability syndrome (FIS) provides a mechanistic framework for non-contact injuries and musculoskeletal complaints. AF-based stability assessment may hold potential for screening and return-to-sport decisions—pending prospective validation.
