Participants
The study included men and women aged 18 years or older who were willing and capable of uploading videos from a smartphone or webcam. People with axSpA were recruited through the local National Axial Spondylosis Society (NASS) network, and people who reported no long-standing back pain were recruited through social media and advertisement. Individuals were excluded from participation if they had surgery within six months, were unable to stand independently, were unable to pass screening questions to participate in physical activity (Physical activity readiness questionnaire, PAR-Q), had a serious neurological condition preventing normal movement or walking ability, or had any severe medical conditions. A minimum of 17 participants were required per group (axSpA and non-back pain groups), assuming 1-beta =0.90, alpha=0.05 and effect size |ρ|=0.50.