Fig. 1

Measurement procedure. (A) Flexion phase trunk extension task. (B) Measurement time point t1. (C) Fully extended position of trunk extension task. (D) Measurement time point t2. The left white cross on the measurement line marks the LD/TLF junction. The white cross on the right marks the center of the artificial reference created by a reflective tape on the skin. TLF, thoracolumbar fascia; LD, latissimus dorsi muscle.