Exercise therapy is prescribed by physiotherapists and rehabilitation practitioners as part of the treatment programme for many movement impairment disorders. Poor adherence and inadequate exercise technique often result in poor outcomes for these patients and delays their return to full physical function. Therapeutic exergaming, which is the use of computer games and body-worn motion tracking sensors to teach therapeutic exercise programmes to patients, may offer solutions to these problems. In this paper we describe one such system, known as FlyFit, which offers a sensor-driven flight game environment that allows physiotherapists to intuitively design game levels that will induce patients to correctly carry out their exercises programme. A 4-week pilot study to investigate the training effect of the system compared to a conventional exercise training approach is described. Results suggest these exergaming systems may induce improvements in balance and strength similar to the conventional programme along with increased levels of intrinsic motivation but further research is warranted.