Objectives: To assess the effects of ankle injury status on intrinsic foot muscle (IFM) size at rest and during contraction in young adults with and without a history of lateral ankle sprain (LAS) and chronic ankle instability (CAI).
Methods: Foot Posture Index (FPI), Foot Mobility Magnitude (FMM), and ultrasonographic cross-sectional area of the abductor hallucis (AbdH), flexor digitorum brevis (FDB), quadratus plantae (QP), and flexor hallucis brevis (FHB) were assessed at rest, and during non-resisted and resisted contraction in 22 healthy (13 females, BMI: 22.5±3.2, FPI: 4.2±3.9, FMM: 2.5±1.8), 17 LAS (9 females, BMI: 24.1±3.7, FPI: 2.5±3.4, FMM: 2.7±1.7), 21 Copers (13 females, BMI: 23.7±2.9, FPI: 3.6±4.1, FMM: 1.8±1.3), and 20 CAI (15 females, BMI: 25.1±4.5, FPI: 4.4±3.6., FMM: 2.3±1.1).
Results: A multiple linear regression analysis assessing group, sex, BMI, FPI, and FMM on resting and contracted IFM size found sex (p<.001), BMI (p=.01), FPI (p=.05), and FMM*FPI interaction (p=.008) accounted for 19% of the variance (p=.002) in resting AbdH measures. Sex (p<.001) and BMI (p=.02) explained 24% of resting FDB measures (p<.001). Having a recent LAS (p=.03) and FMM (p=.02) predicted 11% of non-resisted QP contraction measures (p=.04), with sex (p<.001) explaining 13% of resting QP measures (p=.02). Both sex (p=.01) and FMM (p=.03) predicted 16% of resting FDB measures (p=.01). There were no other statistically significant findings.
Conclusions: IFM resting ultrasound measures were primarily determined by sex, BMI, and foot phenotype and not injury status. The clinical utility of these IFM ultrasonographic assessments in young adults with LAS and CAI may be limited.