Guidelines for the delivery and monitoring of high intensity interval training in clinical populations.

High intensity interval training (HIIT) is now recognized in international clinical-based exercise guidelines as an appropriate and beneficial adjunct to moderate intensity continuous training. HIIT involves alternating periods of high intensity aerobic exercise with light recovery exercise or no exercise, allowing for greater physiological stimulus and adaptation than moderate intensity continuous training (MICT) for cardiorespiratory fitness and other cardiometabolic processes. However, there is no universal criteria or framework for the prescription and monitoring of HIIT in clinical populations, and safety concerns remain a common barrier for implementing HIIT as standard care. Historically, exercise intensity has been prescribed using heart rate (HR) targets derived from either a predicted maximal HR (HRmax) or from an attempt to objectively measure HRmax. However, using this approach alone has a number of limitations. Here we provide guidelines to improve the delivery of HIIT in cardiometabolic populations using 1) a framework for HIIT prescription using a combination of objective and subjective measures of exercise intensity, and 2) clinical considerations for assessment and monitoring to maximize patient safety. The framework involves an individualized step-by-step process to calculate, validate, and calibrate HR target zones for HIIT training to allow for appropriate workload prescription and progression. We strongly recommend this framework be used in future clinical trials investigating HIIT.