In this study, we analyzed facial expressions during muscle strain using a head mounted display (HMD)-based virtual arm wrestling system designed for facial electromyography measurement. We found that facial expressions during muscle strain are characterized by tension of the corrugator supercilii and zygomaticus major muscles. In addition, facial expressions of laughter, anger, and fear, and those during muscle strain can be distinguished based on the active pattern of the corrugator supercilii and zygomaticus major muscles. These findings are useful in the evaluation of emotions based on facial expressions during muscle strain using the HMD-based virtual reality system.