fitness in healthy adults ages 18–45 but HIIT leads to greater improvements in VO2 max. HIIT regimens of one month or longer effectively improve cardiovascular fitness in adolescents and lead to moderate improvements in body composition. HIIT (when defined as four intervals of four minutes at 85–95% of max heart rate with three-minute intervals at 60–70% of max heart rate) is also more effective than moderate-intensity continuous training at improving blood vessel function and markers of blood vessel health. Comparing HIIT to moderate intensity continuous training (MICT) in people with coronary artery disease, HIIT leads to greater improvements in VO2 max but MICT leads to greater reductions in body weight and heart rate. Improvement to cardiorespiratory fitness, as measured by VO2 max, of individuals with lifestyle-induced chronic cardiovascular or metabolic diseases (including high blood pressure, obesity, heart failure, coronary artery disease, or metabolic syndrome) who completed a HIIT exercise program can be nearly double that of individuals who completed a MICT exercise program (19.4% increase and 10.3% increase, respectively). Rehabilitative effects For people suffering from coronary artery disease or heart failure, a HIIT regimen is beneficial for substantially improving both groups VO2 max and overall exercise capacity; with more intense HIIT leading to the greatest cardiovascular improvements. A combination of a proper HIIT program with active recovery instead of passive recovery is most beneficial to improving heart contractibility in people with heart failure. Metabolic effects HIIT significantly lowers insulin resistance compared to continuous training or control conditions and leads to modestly decreased fasting blood glucose levels and increased weight loss compared to those who do not undergo a physical activity intervention. Fat oxidation HIIT can result in modest reductions of subcutaneous fat in young and healthy individuals, but greater reductions for overweight individuals. HIIT, particularly running, is a time-efficient strategy in decreasing abdominal and visceral fat-mass deposits. A 2021 systematic review examined the effects of HIIT combined with resistance training in teens (ages 10–19), without providing a nutritional plan. The study found that 8 to 12 weeks of HIIT combined with resistance training can substantially reduce waist size and body fat percentage. However the study did not find conclusive evidence of HIIT and resistance training being an effective solitary treatment for type 2 diabetes or arterial hypertension, but did find HIIT has the potential to reduce future cardiovascular problems in teens. Brain power HIIT can elicit short term brain improvements