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Why HIIT Improves Cardiorespiratory Fitness More Than Low-Intensity Exercise

High intensity interval training (HIIT) contributes to better improvements in cardiorespiratory fitness as opposed to moderate intensity continuous training (MICT) – or alternatively – low-intensity exercise, according to a review which was published in Frontiers in Cardiovascular Medicine.

Investigators said slowly introducing – as well as progressing – HIIT exercise on a case-by-case basis. This is as opposed to trying a one-size-fits-all model which can reduce musculoskeletal discomfort while maximising safety, adherence, enjoyment in addition to physiological outcomes.

Exercise-based cardiac rehabilitation (CR) is a class 1 clinical practice recommendation for patients with select cardiovascular diseases (CVD) and heart failure with reduced ejection fraction (HFrEF). For patients who have coronary heart disease and heart failure (HF), cardiorespiratory fitness is a very strong predictor of mortality. Owing to this, exercise prescription which optimises improvement in cardiorespiratory fitness and exercise capacity is an extremely critical consideration for the efficacy of CR programming.

Between 2004 and 2011, systematic reviews on coronary heart disease showed that exercise-based CR reduced hospitalisations by 31%, CV mortality by 26% as well as all-cause mortality by 20%, compared with standard medical care. Since then, however, outcomes from RAMIT (the Rehabilitation After Myocardial Infarction Trial) and ensuing systematic reviews questioned the success of exercise-based CR for reducing those outcomes.

What Does A HIIT Routine Look Like?

What distinguishes HIIT (or SIT) from the steady-state, continuous types of exercise — jogging at an even pace or walking, for instance — is the intervals, those periods of heart-pounding intensity. If you would like to try it, you can simply take a HIIT class, or run or even walk in a way which involves higher-speed – as well as higher-incline bursts.

If you would like a routine which has been lab-tested, there’s the 4-by-4 from Norway. It includes a warm-up, followed by four four-minute intervals (again, where your heart rate goes past 80% of its maximum capacity), each interspersed with a three-minute recovery period, and ended off with a cool-down.

So, for instance, you’d jog for 10 minutes to warm up, then perform four four-minute intervals of faster running, with three three-minute intervals of moderate jogging or brisk walking in between, and a five-minute cool down at the end. And you can substitute jogging with other aerobic exercises, such as biking or swimming. The whole routine should take 40 minutes.

A shorter, and also heavily studied, example of an interval routine is the 10-by-1, which involves 10 one-minute bursts of exercise each followed by one minute of recovery.

How Does HIIT Work?

Irrespective of the type of HIIT, it’s thought the health improvements are caused by the rate – as opposed to the amount – at which skeletal muscle glycogen (carbohydrates that are stored by the body for energy) is used. Muscle glycogen is a very important fuel reserve – so our body attempts to replenish it as a priority.

HIIT workouts reduce muscle glycogen at such a rate that the body increases the number as well as activity of mitochondria (powerhouses of cells) in our muscles in order to allow us to meet the energy requirements of exercise. This in turn leads to increases in fitness, metabolic function as well as health.

Again, these routines look pretty different from what’s on offer at chains such as Virgin Active and Planet Fitness, or even the seven-minute workout. Even though they’re frequently referred to as HIIT, they mix cardiovascular exercise with strength training.

Contact Trifocus Fitness Academy

If you would like to become a HIIT trainer then you need to do our HIIT and Functional Trainer Course. Follow this link to find out more.

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