The mechanism of astronaut injuries inside rigid spacesuits is not well understood, due to difficulty visualizing intra-spacesuit body motions. An alternative method is to record muscle activation signals with electromyography (EMG); however, the conventional EMG procedure requires bulky, extensive electrode/wire setup and is susceptible to signal noise. To address these challenges for aerospace applications of EMG, we designed a garment-based system to collect EMG data from upper body muscle activities inside spacesuits. Constructed with form-fitting textiles and careful management of on-garment tensions, our garment provides a viable non-invasive EMG study solution that maximizes applicability and subject mobility while resisting motion artifacts. The functionality and usability of our design was also validated with a human subject test, which showed standard-quality signal, easy don/doff process, minimal electrode/wire setup, and simple wire bulk management, as opposed to the conventional methods.