The nature of our research with tactical personnel requires that we conduct most of our work in dynamic and often austere environments while these personnel are doing highly physical tasks. While capturing energy expenditure is often a key requirement, pragmatically we have not been able to do this given the requirement for bulky, generally static, equipment. The VO2 Master has been a game changer. Being so small and portable we have been able to use it in a variety of projects, from mounted police on horseback to specialist police conducting occupationally specific capability testing. Best of all it works easily with some of our other equipment (e.g., polar HR monitors) and iPads and allows use to monitor and show other researchers and personnel data in real-time.