The rise of Virtual Reality (VR) sports has been driven by evolving work patterns, limited access to physical exercise spaces, and a growing focus on health and wellness. Beyond the enjoyment and convenience offered by VR exercise, we aim to enhance users' athletic performance through this medium. Prior research on the Proteus Effect in VR sports has demonstrated the potential of customized, stronger, or younger avatars to improve exercise outcomes. However, such effects are limited for users who already perceive themselves as strong and youthful. To address this, we propose a more general approach: representing perceived avatar capability through facial expressions and vocal cues to influence user performance. In this study, we examined how manipulating the perceived capability level of virtual avatars (high, neutral, low) during dumbbell lateral raises in a VR gym affected exercise performance. Results indicated that avatars with high-capability expressions significantly enhanced performance and motivation compared to low-capability avatars. These findings underscore the promise of using facial and auditory cues to represent perceived capability, offering new directions for designing emotionally intelligent fitness applications.