DANGER ZONE

Orangetheory classes are split into running intervals, rowing and resistance circuits (see the box opposite for details of my first class). Everyone is strapped up to Polar HRMs, with big TVs above the treadmills highlighting our individual bpm so you and everyone else can see how hard you’re pushing.

There are five heart rate zones, ranging from grey for very light to red for maximum. Your orange zone starts at 84% of your max heart rate, and it’s above this mark that you’re meant to spend 12-20 minutes of the 60-minute session. According to instructor Emmanuel Olaojo, this sparks your body’s excess post-exercise oxygen consumption (EPOC) effect, ‘helping you burn between 400-500 extra calories over the following 36 hours’.

I’m surprised at how hard I have to work to hit the orange zone. The class is seriously fast-paced, with the intensity high on the treadmill and circuit stations, although a block of isolation exercises allows me to catch my breath. At the end of the hour I’m given my stats: I spent 39min of the time in the orange and red zones (you’re likely to spend more time in them if you’re less fit) and torched 813 calories.

THEORY OF EVERYTHING

My body might have turned into a calorieincinerating furnace for an hour, but it’s the ensuing 36-hour afterburn I’m intrigued about. If my body were to consume a further 400 calories while it recovered, that would equate to 50% of total energy expenditure during the class. However, a 2006 review of the research published in the Journal Of Sport Science suggests the EPOC from intense exercise only ranges between 6-15%. And if you’re already mighty fit, it can be as low as just 1% because you recover quicker.

Fat-burning zones are a contentious area.