Outcome measures
Each outcome variable and its measurement method were described in detail in the study protocol paper [Back extensor muscle strength was the primary outcome measure. This was measured using an isokinetic dynamometer (Biodex Multi-Joint System; Biodex Corporation, Shirley, NY, USA). Briefly, the examination was performed by comfortably seating the participant in the device, fixing both the legs and back to the machine using a strap. Subjects were instructed to flex and extend their backs five times at an angular velocity of 60°/s as a warm-up before the examination. During the test, subjects were instructed to perform maximum effort back flexion and extension 10 times, with a 60°/s angular velocity. The back range of motion was limited to 50° with 30° (− 30°) flexion and 20° (+ 20°) extension relative to the anatomical reference position (0°) [Secondary outcome measures were performed as follows [