Üsen A, et al. - The experts attempted this study to compare abdominal muscle thickness in ankylosing spondylitis (AS) patients with healthy subjects and to evaluate the factors affecting these muscle thickness. They disclosed that in AS patients, muscle thickness of the internal oblique (IO), external oblique (EO), and transversus abdominalis (TrA) muscles were similar to healthy subjects. However, they also reported the reduced thickness of IO and TrA muscles in AS patients who had a lower level of physical activity.

• This study enrolled 35 male patients with a previous diagnosis of AS according to the Modified New York criteria and a control group consisting of 35 healthy male individuals. 
• With the aid of ultrasound (US), thicknesses of the internal oblique (IO), external oblique (EO), and transversus abdominalis (TrA) muscles were measured.
• According to the International Physical Activity Questionnaire (IPAQ), AS patients were classified.
• There were 35 AS patients with a mean age of 35.17 ± 8.05 years and 35 healthy subjects with a mean age 32.57 ± 7.05 years.
• Between the groups, no significant difference was observed in terms of abdominal muscle thicknesses (p > 0.005). 
• When the AS patients were classified according to the IPAQ scores, thicknesses of the IO and TrA muscles were significantly lower in patients who had the low level of IPAQ scores (p < 0.05).