HIIT it hard

It’s the most popular trend in fitness – and the most misunderstood. Use the latest science to rethink your high-intensity training and make big gains

Fight fat more effectively with highintensity workouts. Our feature tells you all you need to know

It may have achieved unprecedented popularity in the past few years but whatever you’ve heard, high-intensity interval training (HIIT) isn’t new. In 1912, Finnish athlete Hannes Kolehmainen used interval-style training in his preparation for the Olympics, and came away with three golds in the 5,000m, 10,000m and cross-country events. In 1952 Emil Zátopek, one of the most celebrated distance athletes of all time, won the Olympic marathon on a regime that included 400m interval sprints. And in the 1970s, Sebastian Coe’s father Peter used HIIT principles to create sessions of repeated 200m sprints that shaped his son into one of Britain’s best ever middle distance runners.

What’s changed since then is the science. You’ve probably heard of the Tabata regime – eight sets of 20 seconds’ high-intensity work with ten seconds of rest, based on a 1996 study by Professor Izumi Tabata – but that research is just the tip of the iceberg. In recent decades, there’s been a huge amount of research into exactly how different work-rest intervals, levels of intensity, and movements affect the results you get from HIIT.

And yet, when a lot of trainers explain it, the only description given is “hard work, short rests”. In short, there’s a better way to do HIIT.

HIGH ENERGY

First, it’s important to understand that while HIIT is an effective fat burner, it has a host of other benefits: upping your VO2 max (the amount of oxygen your body can use and an indicator of cardio fitness), reducing lactate accumulation (so you can train harder, for longer), and increasing enzyme activity to reduce fatigue. When you start, almost any format will work, but as you get better adapted to the workout method, tweaking your routine will help you focus on what you need to improve.

It starts with your body’s energy pathways. There are three: the ATP-PC, which fuels high-power, short-lived activities like explosive weightlifting or sprints; the glycolytic, which takes over for moderateduration activities; and the oxidative, which is in control for anything beyond that. The first two are anaerobic, which means they don’t use oxygen, and the last is aerobic because it does. HIIT works both your aerobic and anaerobic systems, but how it works the different energy pathways depends on the work/rest ratios you’re using.

In a 2001 study, for instance, researchers found that the aerobic system’s contribution to energy rockets from 6% after ten seconds of exercise to 45% after 60 seconds. But the same happens during repeated sprints: in one Loughborough University study, the anaerobic systems provided all of a test subject’s energy for the first of ten sixsecond sprints (with a 30-second rest), but by the end they were supplying around 35%, with the rest coming from aerobic fitness.

What does that mean? Well, it means that 30 seconds’ rest isn’t enough to improve power, but the main takeaway should be that your workout doesn’t have to leave you in a pool of sweat on the floor (depending on your aim). A 2011 study published in the Journal Of Strength And Conditioning Research found that test subjects doing a “descending” sprint protocol, which was rated easier than an “ascending” protocol that used the same distances, experienced a higher rise in growth hormone and testosterone. Sometimes, it’s not about how exhausted you feel.

FEEL THE BURNOUT

If you’re feeling worn down in the first place, of course, HIIT isn’t the session to go for. “A common mistake with HIIT is the assumption that it trumps steady-state cardio at all times, which isn’t true,” says trainer David Jordan (thefittingrooms.com). “HIIT is highly effective because it requires less time and burns calories during recovery. However, to reap the benefits of HIIT you need to attack it with a lot of energy. On days when you’re feeling less than 100% or, more importantly, you’re sore from your previous workout and are at risk of pulling a muscle, then steady-state cardio is probably more effective – and safer.”

Finally, it’s important to consider how often you can do “real” HIIT. “It’s true that HIIT can trigger protein synthesis but it also causes protein breakdown,” says Jordan. “Doing several HIIT sessions a week would be catabolic so while you’d lose weight overall, some of that loss would be muscle mass. If building muscle is a goal, proper weight training still needs to be your primary focus with HIIT as a supplement. A training split of two weights sessions and two HIIT a sessions a week would keep you lean, while making sure you aren’t overtrained.”

Remember: it’s supposed to be short, intense and infrequent, not an everyday effort. Read on to find out how to structure your HIIT workouts.