Muscle stability deficits and musculoskeletal complaints in football players: Adaptive Force Ratio outperforms conventional strength parameters--a cross-sectional study with preliminary follow-up
- 1Center of Orthopedics, Traumatology and Plastic Surgery, University Hospital Brandenburg, Brandenburg Medical School Theodor Fontane, Brandenburg an der Havel,
Abstract
Strength-based screening has documented limitations. Adaptive Force (AF) offers an alternative--it captures the adaptive holding capacity under rising external load, not addressed by strength testing. This study examined the association between AF-based muscle stability and musculoskeletal complaints in 23 football (soccer) players, comparing AF-derived and conventional strength parameters, with preliminary follow-up. AF and maximal voluntary isometric contraction (MVIC) were measured 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 by complaint status assessed via questionnaire at baseline and six-month follow-up (n=13).
Stability deficits were strongly associated with complaints (OR=54.0, 82% side concordance). AF-Ratio discriminated 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 outperformed both at baseline (p[≤]0.002) and follow-up (p[≤]0.028).
AF-based stability assessment may capture neuromuscular deficits related to complaints that conventional strength testing misses, with preliminary follow-up data suggestive of predictive value. The concept of functional instability syndrome provides a mechanistic framework for non-contact injuries and complaints. AF-based stability assessment may hold potential for screening and return-to-sport decisions--pending prospective validation.
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BibTeX
@misc{schaefer2026muscle,
title = {{Muscle stability deficits and musculoskeletal complaints in football players: Adaptive Force Ratio outperforms conventional strength parameters--a cross-sectional study with preliminary follow-up}},
author = {L. V. Schaefer and F. N. Bittmann and J. Ulrich and R. Prill and R. Becker},
howpublished = {medRxiv},
year = {2026},
month = jul,
doi = {10.64898/2026.07.07.26357205},
url = {https://www.medrxiv.org/content/10.64898/2026.07.07.26357205v3},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Muscle stability deficits and musculoskeletal complaints in football players: Adaptive Force Ratio outperforms conventional strength parameters--a cross-sectional study with preliminary follow-up
AU - L. V. Schaefer
AU - F. N. Bittmann
AU - J. Ulrich
AU - R. Prill
AU - R. Becker
PY - 2026
DA - 2026/07/07
PB - medRxiv
DO - 10.64898/2026.07.07.26357205
UR - https://www.medrxiv.org/content/10.64898/2026.07.07.26357205v3
AB - Strength-based screening has documented limitations. Adaptive Force (AF) offers an alternative--it captures the adaptive holding capacity under rising external load, not addressed by strength testing. This study examined the association between AF-based muscle stability and musculoskeletal complaints in 23 football (soccer) players, comparing AF-derived and conventional strength parameters, with preliminary follow-up. AF and maximal voluntary isometric contraction (MVIC) were measured 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 by complaint status assessed via questionnaire at baseline and six-month follow-up (n=13). Stability deficits were strongly associated with complaints (OR=54.0, 82% side concordance). AF-Ratio discriminated 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 outperformed both at baseline (p[≤]0.002) and follow-up (p[≤]0.028). AF-based stability assessment may capture neuromuscular deficits related to complaints that conventional strength testing misses, with preliminary follow-up data suggestive of predictive value. The concept of functional instability syndrome provides a mechanistic framework for non-contact injuries and complaints. AF-based stability assessment may hold potential for screening and return-to-sport decisions--pending prospective validation.
ER -