Inclusion Criteria:  Age: 18-70 BMI: 18.5-40 Inflammatory joint disease verified by physician Able to walk unaided and continuously for ≥ 15 min. Norwegian or English speaking  Exclusion Criteria:  Sustained lower extremity injury ≤12 months, including surgery Neurological disease Absolute contraindication to maximal exercise test Cognitive impairment Participation in structured high-intensity exercise ≥ 1/week in the last 3 months