High-intensity interval training (HIT) has been demonstrated to be an effective strategy to improve markers of health and fitness across a wide range of healthy and clinical populations. Currently however, there is only limited evidence which has examined the effectiveness of HIT in older adults (>50 years). HIT is an appealing strategy in this group as it has the potential to impact both cardiorespiratory and muscular fitness, which both play an important role in maintaining functional fitness and quality of life in a time-efficient manner. Developing an understanding of novel strategies for delivering this type of exercise training may ultimately provide a viable alternative to traditional modes of exercise training for a broader range of participants. As such, the purpose of this study is to evaluate the effects of a novel, high-intensity interval training exercise protocol to improve physical fitness in adults aged over 50 years. This research also aims to evaluate if this type of training intervention is feasible in this population, through analysis of adherence and intervention fidelity.