Van enkelverstuiking naar chronische enkelinstabiliteit: studie naar de pathomechanische gewrichtsbelasting van de voet tijdens sporttaken en de eigenschappen en functies van intrinsieke voetspieren.

Chronic ankle instability (CAI) is a frequent consequence of lateral ankle sprains, characterized by persistent symptoms and functional deficits, whereas copers recover with minimal impairments. Altered movement patterns, muscle strength, and muscle sizes are thought to contribute to this continuum, yet ankle and foot joint biomechanics during change-of-direction tasks and the role of intrinsic foot muscles (IFMs) remain poorly understood. This PhD aimed to compare ankle and foot joint dynamics among individuals with CAI, copers, and healthy controls during side-step cutting, and to investigate IFM sizes, strength, and fatigue-related effects. Methodologically, it evaluated IFM strengthening interventions, the reliability of low-end ultrasound imaging, and different foot muscle fatigue protocols. Meta-analyses showed that IFM exercises and minimalist footwear may induce trivial to moderate increases in IFM size and foot strength, albeit with very low certainty of evidence. Exercises reduced medial longitudinal foot mobility, whereas minimalist footwear promoted a more forefoot-oriented running pattern. Experimentally, concentric toe flexor contractions induced twenty percent hallux flexion strength decline, indicating fatigue, whereas isometric contractions combined with electrical stimulation did not. Both interventions acutely modified running ground reaction forces. Ultrasound imaging with a low-end device demonstrated moderate to good test-retest and inter-rater reliability when measuring identical images, but poor reliability when image acquisition was included. During anticipated 45° side-step cutting, foot joint kinematics were largely similar across groups, although individuals with CAI showed trends toward altered ankle, midfoot, and hallux kinetics, as well as reduced posterior ground reaction forces. IFM sizes did not differ between groups, but hallux flexion strength was lower in CAI and copers compared to controls. Following isometric contractions plus electrical stimulations, individuals with CAI exhibited a moderate strength decline and changes in ankle and foot joint dynamics. Overall, this PhD highlights the multifactorial and heterogeneous nature of CAI, in which subtle kinetic, neuromuscular, and sensory-perceptual alterations coexist. These findings support investigating CAI using task-specific, integrative, and longitudinal approaches that account for symptom severity, functional subgroups, and neurocognitive demands. Advancing foot assessment methods, refining conceptual models, and evaluating targeted treatment modalities are essential to better understand the mechanisms underlying CAI and to optimize individualized rehabilitation.