Sufficient physical activity and a good cardiorespiratory fitness level (CRF) are central in cardiovascular disease (CVD) risk reduction. However, many people remain inactive, partly because current exercise recommendations fail to address important barriers to exercise. A novel exercise protocol has previously been developed called 'reduced-exertion high-intensity interval training' (REHIT), which can remove several common perceived barriers to exercise. REHIT 1) improves CRF and other key CVD risk factors, 2) is genuinely time-efficient (total time-commitment of just 2x10 min per week), 3) is well-tolerated, manageable, and not associated with negative affective responses, and 4) can be done in the workplace, in work-clothes and without a need to shower afterwards. To date, this intervention has only been investigated in a lab-setting. Therefore, in the present randomised controlled trial, the 'real-world' effectiveness of REHIT in improving maximal aerobic capacity (V̇O2max; a key risk factors of CVD) will be investigated in a workplace setting. Participants' attitudes and psychological responses to REHIT will be assessed to evaluate the likelihood of successful implementation. In 2 study centres, a total of up to n=50 physically inactive male and female office workers will be recruited to perform 6 weeks of unsupervised, computer-guided, office-based REHIT (n=25) or act as a control (n=25).

Inclusion Criteria:

• Employee at participating workplace

Exclusion Criteria:

• Aged < 18 years or > 60 years
• History of type 2 diabetes
• Insulin therapy
• Use of β-blockers
• Use of inhaled steroids (e.g. for asthma)
• Any cardiovascular condition with the exception of well-controlled uncomplicated hypertension (systolic >140 mm Hg and/or >90 mm Hg after at least 5 minutes of seated rest), which is treated with no more than two drugs (either an ACE, ARB, calcium channel blocker, or diuretic)
• Cerebrovascular disease including previous stroke or aneurysm
• History of exercise-induced asthma
• History of type 1 diabetes mellitus or a history of ketoacidosis
• History of other specific types of diabetes (e.g., genetic syndromes, secondary pancreatic diabetes, diabetes due to endocrinopathies, drug or chemical-induced, and post organ transplant)
• History of respiratory disease including pulmonary hypertension or chronic obstructive pulmonary disease
• History of musculoskeletal or neurological disorders
• Active inflammatory bowel disease
• History of renal disease
• Other metabolic diseases, including hyper/ hypo-parathyroidism, hyper/hypo-thyroidism, and Cushing's disease.
• BMI>35 kg/m2
• A clinically significant resting ECG abnormality at the pre-screening visit which in the opinion of the cardiologist exposes the participant to risk by take part in the main trial.
• 'Yes' to any questions on a standard physical activity readiness questionnaire (PARQ)
• Classification as moderately or highly physically active on the International Physical Activity Questionnaire (IPAQ)
• Current participation in another research study
• Inability to fully understand the verbal and written descriptions of the study in English, and the instructions provided during the study

data will be disseminated / published as means +- SD. no individual data will be presented.