Video Coaching of Physical Activity in Axial Spondyloarthritis

The primary objective of the study is to demonstrate the beneficial effect of a 3 months home-based physical exercise program supervised by online videos, in addition to the usual recommendations, in comparison with usual physical activity as recommended by the WHO. The secondary objectives of the study are : 1. to compare the following criteria between 2 groups at 3 and 6 months: * quality of life; * other measures of disease activity ; * sleep quality ; * walking ability * muscle strength of; * professional activity; * cost of cares; * evolution of weight, BMI and waist. 2. to evaluate the observance of physical activity program and its tolerance at 3 and 6 months.