©2015 Japanese Society for Magnetic Resonance in Medicine. We constructed an arm holder for muscle exercise from a forearm-shaped plastic shell and magnetic resonance (MR) imaging position markers and determined the echo time (39ms) for T2-weighted spin-echo MR imaging from T2 values of the exercised (50ms) and resting (32ms) muscle at 0.2 tesla. The smallest detectable muscle was the extensor digiti minimi muscle (cross-sectional area 25mm2). This combination could be useful to monitor finger exercise in patients undergoing physical therapy.