Heart failure (HF) is a condition associated with high levels of morbidity and mortality. For people with this condition, exercise training is recommended as part of standard management as it improves exercise capacity, symptoms and quality of life and has been shown to reduce hospital readmissions. Guidelines recommend that all people with stable HF undertake 150 minutes of moderate intensity activity per week. For many years, centre-based exercise programmes, such as cardiac rehabilitation or HF rehabilitation, have been the traditional approach to assist individuals to meet these guidelines, however, uptake at these programmes is poor and recent studies suggest that fewer than 40% of people with HF meet recommended physical activity targets. This has led clinicians to deviate from the traditional “one size fits all” exercise model in search of strategies which assist individuals to attend these programmes, and to explore alternative exercise opportunities to increase exercise adherence at scale. This thesis aims to examine exercise participation in people recently hospitalised with HF and to explore aquatic exercise training as a potential exercise option for this population. The thesis was developed in two parts. Section one (Studies 1 and 2) aimed to describe and identify variables associated with exercise participation and exercise capacity measured by six minute walk distance (6MWD). Study 1 was a sub-study of the EJECTION-HF trial, a multicentre randomised controlled trial which investigated the impact of supervised exercise training in addition to a disease management programme, in people recently hospitalised with HF. Primary outcomes of this trial were death or readmission at 12 months. The objectives of Study 1 were to describe exercise participation in this clinical HF population and to identify variables related to exercise participation which are associated with improvements in 6MWD. Data were available from 140 participants for exercise programme attendance variables and 117 participants for self-reported physical activity undertaken outside of the health facility. Results confirm that exercise participation is poor in this cohort and also identify that frequent exercise programme attendance (at least weekly) and being physically active (meeting exercise guidelines), are independently and strongly associated with improvements in functional exercise capacity. Following on from these findings, Study 2 sought to identify predictors of these important variables (frequent programme attendance and meeting exercise guidelines). This study was also a sub-study of the EJECTION-HF trial. Variables entered into logistic regression models included common participant and clinical characteristics such as age, gender, HF aetiology, disease severity, new versus decompensated HF, presence of comorbidities and baseline physical activity. Findings indicated that a new diagnosis of HF was strongly associated with exercise participation, including both frequent programme attendance as well as meeting exercise guidelines. Baseline physical activity was also associated with being physically active at 12 weeks. Results from Studies 1 and 2 provide new insight into the exercise behaviour of people recently hospitalised with HF and identify opportunities for clinicians to target exercise services more specifically for greatest effect. Section two of this thesis (Studies 3, 4 and 5) aimed to explore the safety, efficacy and acceptability of aquatic exercise training, thus determining if this mode of exercise is a suitable option for people with HF seeking alternative exercise opportunities. Study 3 produced a systematic review and meta-analysis of existing literature with particular focus on the impact of aquatic exercise training interventions on exercise capacity, muscle strength, quality of life, haemodynamics and B-type natriuretic peptide. Compared to no exercise controls, aquatic exercise training was associated with significant improvements in exercise capacity, muscle strength and quality of life. Based upon the absence of serious adverse events in any of the small studies included in this review, aquatic exercise training was deemed to be safe for people with stable HF. Study 4 expanded on these findings by examining the feasibility and efficacy of aquatic exercise training, compared to a land-based exercise programme in a clinical environment. This randomised 2x2 crossover design trial enrolled people with HF who were in an exercise training maintenance phase at two metropolitan hospitals and compared six weeks of aquatic and land-based exercise training with respect to 6MWD, grip strength and measures of balance. Data from 51 participants with stable HF confirmed that aquatic exercise training is safe and feasible in a clinical environment and is equally effective as land-based exercise training for maintaining each of the outcome measures listed above. This study also identified biventricular HF as a potential contraindication for this type of exercise training. Study 5 aimed to explore individuals’ experiences with aquatic and land-based exercise training using a mixed methods approach to determine acceptability of aquatic exercise training in a clinical HF population. A purpose designed questionnaire gathered information about experiences and preferences and was provided to participants at the completion of Study 4. Semi-structured interviews further explored perceptions, experiences, motivators and barriers to exercise participation in 14 participants, seven of whom had chosen not to participate in the aquatic programme. Results confirmed that people with HF perceive aquatic exercise training to be a safe, acceptable and enjoyable mode of exercise, similar to land-based exercise training. Latent fatigue was identified as a common symptom of the aquatic programme, however was not associated with the landbased programme. Important motivators for exercise participation were identified and included a skilled and compassionate workforce, sense of safety, perceived benefit, programme tailored to the individual and sense of inclusiveness and enjoyment. These themes were common to both exercise interventions. This thesis, in two sections, examines concepts relating to exercise adherence in a clinical HF population. Section one describes exercise behaviour in people recently hospitalised with HF and explores variables associated with both exercise participation and outcomes. These studies identified potentially vulnerable groups who are less likely to meet recommended exercise guidelines, thus presenting opportunity to tailor services for best effect. Section two presents a comprehensive report of aquatic exercise training in people with HF. Based upon these results, this mode of exercise is safe, effective and acceptable for people with stable HF and thus provides an additional and viable option for these individuals to be physically active.