In video 1: if you have low back pain, please be careful and not

In video 2:  When you horizontally adduct your arm, it doesn't have any help, instead, it will create discomfort and dysfunction to the upper back or shoulders and make it worse. In fact, we live in flexion everyday. Moving your arms in horizontal abduction position will release and lenthen the muscles in the chest, in the mean time, strengthening the muscles in the upper back.