Effects of Traditional Chinese Exercise Yijinjing on Disability and Muscle Strength Among Patients With Chronic Low Back Pain: Protocol for a Randomized Controlled Trial - Lei Guo; Cheng Wang; Xue Bai; Yukui Tian; Mengni Shi; Min Fang; Jing Xian Li; Qingguang Zhu; Junchang Liu (JMIR Research Protocols)