How high-intensity interval training will work for you

If you haven’t heard about high-intensity interval training, we’ll assume you’ve been living in a cave or on another planet for the last year. HIIT is hot – and its popularity is growing.

Pete McCall is a huge fan of HIIT. He’s also an exercise physiologist, trainer, group fitness instructor, educator and general fitness guru. Pete recently shared with us his thoughts on HIIT, the science behind it and why it works. This is what he had to say …

High-Intensity Interval Training, which incorporates short intense bursts of effort, followed by recoveries, has become a permanent feature on the training schedule of exercise lovers – and with good reason. It gets results, and gets them fast.

Even the American College of Sports Medicine (ACSM)’s annual survey of thousands of fitness professionals identified HIIT as the top fitness trend for 2014.

HIIT workouts feature periods of high intensity exercise followed by rest intervals. Examples of HIIT include a 40-meter sprint followed by a walk back to the start, ten explosive jumps followed by a plank exercise or medicine ball throws followed by a set of bodyweight squats. The point of HIIT is to go as hard as possible for a brief period, then allow the body to rest and repeat. There is a lot of research which demonstrates that HIIT is effective for both weight loss and improving overall fitness levels. If you’ve ever participated in a HIIT workout then you know how challenging it is, but have you ever wondered why it is so effective? If you’ve never tried a HIIT workout then you should, especially once you see how it can help you achieve the body you want.

‘‘ The higher the intensity, the longer the EPOC effect and the more calories you’ll burn after the workout. ’’

-Pete McCall

Here’s a brief overview of the science behind HIIT. Muscle contractions require energy known as adenosine triphosphate (ATP). ATP can be produced one of two ways: either with oxygen from the aerobic pathways or without oxygen from the anaerobic pathways. The aerobic pathways are efficient when muscles need a consistent amount of force over an extended period of time like when walking, cycling or jogging. The anaerobic pathways produce ATP up to six times quicker and are used when muscles need energy immediately to generate high amounts of force for activities like sprinting or heavy weight lifting. In general the anaerobic pathways can produce enough ATP to fuel approximately 15-90 seconds of work, the higher the intensity-the faster the supply of ATP is depleted. Once anaerobic contractions have exhausted the immediate source of ATP the aerobic system kicks in to help refuel the muscles.

It’s important to note that the human body uses approximately five calories of energy to consume a liter of oxygen to fuel muscle activity; the higher the intensity – the more oxygen used and the more calories burned. In general HIIT works by exhausting the ATP available in the anaerobic pathways during the work interval and then relying on the aerobic pathways to refuel the ATP during the active recovery interval. Here’s one cool feature of HIIT – not only will you burn calories during the high intensity portion, but you will also burn calories during the lower intensity recovery as your body uses oxygen to restore the ATP which will fuel the next phase of anaerobic conditioning.

A second feature of HIIT is that it supports muscle growth. Adults lose lean muscle mass during the aging process and exercise which promotes muscle growth can actually provide an anti-aging effect. If you’ve done HIIT then you know that burning you feel in your muscles? It’s the waste produce (think exhaust) of muscle contraction and includes lactic acid and hydrogen ions technically referred to as acidosis. As your fitness levels improve, then your muscles increase their tolerance and ability to deal with this waste. The really cool thing is that the exercise intensity which increases acidosis also stimulates production of the hormones – Testosterone (T), Growth Hormone (GH) and Insulin-like Growth Factor (IGF-1) which can help you increase your lean muscle mass and retain a more youthful appearance.

The final, and best, benefit of HIIT is that your body continues to burn calories once the workout is over thanks to a physiological feature known as Excess Post-Exercise Oxygen Consumption (EPOC). During the period after HIIT EPOC means the body continues to uses oxygen at the rate of five calories a liter to perform the following functions: restore ATP used during the workout, work with protein to repair damaged muscle tissue and restore body temperature to normal resting levels. The higher the intensity of the HIIT intervals, the longer the EPOC effect and the more calories you’ll burn after the workout.

If you’re keen on experiencing the benefits of HIIT then a LES MILLS GRIT™ workout might be perfect for you. The thirty-minute workouts feature a variety of high-intensity exercises that will challenge your entire body and even though you’ll be exhausted you’ll find yourself looking forward to the next class.

If you want to learn more about the science of HIIT and how LES MILLS GRIT™ get results check out the Les Mills Knowledge hub.

If you want more health and fitness inspiration simply sign up to Fit Planet and get the freshest insights and advice straight to your inbox.