Iliopsoas strengthening increases hip joint forces during gait: A simulation study.

Femoroacetabular impingement syndrome (FAIS) is a common source of hip pain in young, active individuals and treatments have yielded variable success rates. Weakness of the hip flexors in individuals with FAIS often fails to be resolved during treatment and has been correlated to worse patient reported outcomes and joint damage. This study used musculoskeletal modeling to investigate the differences in iliacus and psoas force production and JCFs during walking between individuals with FAIS and healthy controls (HCs) and to simulate hip flexor strength and weakness in participants and evaluate the resulting changes in JCFs during walking. Five conditions of iliacus and psoas strength were evaluated: 50%, 75%, 100%, 125%, and 150% of the model's default strength. Statistical parametric mapping was used to compare outcomes between groups and between flexor strength conditions. There were no significant differences between the FAIS and HC groups. Increased flexor strength caused higher resultant JCFs and directional components of the JCF throughout the gait cycle. Decreased flexor strength caused lower JCFs across most of the gait cycle; there was no difference in the resultant or superior JCF during preswing and the medial JCF was higher during a small percentage of preswing. These findings indicate that increasing hip flexor strength may have a more uniform effect on JCFs while decreasing flexor strength results in more varied effects between individuals and across the gait cycle.