Handball is one of the Olympic sports with the highest incidence of injury and chronic ankle instability is a common injury among handball players. Strong evidence shows the relevance of the core system in lower limb biomechanics and injury risk; however, few research has been published regarding the role of the active subsystem of the core on chronic ankle instability. The objective has been to compare abdominal wall morphology and function between young handball players with and without chronic ankle instability. Case–control study with 100 young handball players, 50 males participants and 50 females participants, was recruited and divided into athletes with chronic ankle instability (case group, n = 50) and healthy athletes (control group, n = 50). Main outcome measures were morphology and function of abdominal muscles and the inter-recti distance assessed by ultrasound examination. Significant between-group differences were found in the resting assessment of right rectus abdominis (case group 1.12 cm; control group 1.04 cm; p = 0.049), left rectus abdominis (case group 1.16 cm; control group 1.06 cm; p = 0.037), left internal oblique (case group 1.00 cm; control group 0.88 cm; p = 0.012), left transversus abdominis (case group 0.38 cm; control group 0.34 cm; p = 0.039) and inter-recti distance (case group 1.20 cm; control group 1.40 cm; p = 0.049). Moreover, significant between-sex differences were found in almost all morphological outcomes; muscle size at rest was larger in male handball players than in women counterparts. By contrast, no significant differences were found for function outcomes. Young handball players with chronic ankle instability had greater resting thickness of some abdominal muscles and lower inter-recti distance when compared to healthy athletes.
