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Trials in COPD have shown that HIIT leads to the same positive outcomes as constant load training but causes less breathlessness and leg discomfort during training. However, HIIT protocols in existing trials have all been different and use relatively long interval durations (30 s) and short rests. This is sub-optimal because long interval durations lead to greater breathlessness and patients may fear that they will not fully recover during short rests, potentially decreasing adherence. A novel HIIT protocol involving very brief intervals (e.g. 10 s) with longer rests may provide the same benefits with less distress due to breathlessness.

Chronic Obstructive Pulmonary Disease (COPD) is a common and disabling smoking-related lung disease that is predicted to become the 3rd leading cause of death world-wide by 2030 (WHO, 2017). The economic burden of COPD in the United Kingdom is estimated by the British Lung Foundation (BLF) to be around £48.5 billion per year - higher than all other respiratory diseases, including lung cancer. Although widespread, Hull is a COPD 'hot spot' (BLF), with prevalence and mortality rates 36% and 75% higher than the national average, respectively. COPD is characterised by symptoms of breathlessness and cough that typically progress over time.

As a consequence of these symptoms, physical activity (PA) is reduced in COPD patients, with lower levels associated with higher symptom burden, hospital admissions and mortality. Breathlessness is the most commonly reported barrier to PA in COPD, resulting in a cycle of deconditioning that ultimately leads to greater breathlessness and disability.

Pulmonary rehabilitation (PR) improves symptoms and increases exercise capacity in COPD but uptake and adherence are poor. Patients with greater breathlessness are less likely to complete PR programmes which is unsurprising given that exercise-induced breathlessness can be distressing in COPD.

One potential solution is high-intensity interval training (HIIT). HIIT involves short bursts of high-intensity exercise interspersed with periods of rest. The short duration of high-intensity exercise can reduce distressing breathlessness during exercise in COPD, mitigating the most common barrier to exercise.

As mentioned above, PR participants benefit from increased exercise capacity. However, what patients can do (exercise capacity) does not always translate into what patients do (PA) and the effect of PR on PA has been disappointing.

Interventions that aim to improve PA in COPD patients have been trialed, but the quality of evidence is low and results inconsistent. Physical inactivity is the strongest predictor of mortality in COPD patients and therefore, effective interventions that increase PA are desperately needed.

Inclusion Criteria:

• Mild, Moderate and severe* COPD forced expired volume (FEV-1) ≥30 with an FEV-1/ forced vital capacity (FVC) ratio <70%) confirmed on spirometry within 6 months of recruitment.

  • Chronic breathlessness that limits exercise capacity (mMRC ≥2).
  • Using inhaled therapy for COPD including a long-acting bronchodilator agonist (LABA and/or long acting muscarinic agonist (LAMA) with or without inhaled corticosteroids (ICS).
  • Oxygen saturations ≥90% breathing room air.
  • Willing and able to undertake study procedures.
  • Has provided informed consent. * Mild and Moderate COPD patients will be recruited from the start of the study. A review of exercise session completion rates and adverse events will be performed after 10 patients have been recruited to assess the tolerability and acceptability of the different HIIT protocols prior to beginning recruitment of people with severe COPD

Exclusion Criteria:

• Significant physical or psychological comorbidity considered by the investigator likely to affect study outcomes.

  • Active cardiovascular disease or recent significant cardiovascular event (myocardial infarction within 6 months, cardiac arrhythmias including atrial fibrillation/flutter within 6 months, unstable angina within 6 months, stable angina with current symptoms).
  • Moderate or severe COPD exacerbation within 4 weeks of screening (an exacerbation requiring treatment with steroids and/or antibiotics or leading to hospitalisation).
  • Unable or unwilling to undertake exercise as set out in the study protocol

Random order of the delivery of the HIIT protocol