This paper describes the design and evaluation of a wearable Personal Wellness Coach system that supports a range of activities including health data collection, interpretation, feedback and self-monitoring. We implemented a wearable computing platform consisting of an array of sensors and application software to motivate users to reach fitness goals and prevent harm in a real-time environment. Evaluation and testing were done on 65 users in four groups: students, health club members, ROTC members and Baby Boomer-age individuals. Comparing the Personal Wellness Coach against an existing exercise product, our results indicate that this system is an effective tool that is less intrusive and in some cases can perform like a personal trainer and help improve user efficiency.