If you want to benefit from the afterburn effect, you have to ask just a little bit more from your body than it can handle that day. While that’s almost the definition of ‘tough’ (and it has to be if you want to see results), a session isn’t an exercise in torture. There’s certainly no boot camp-style sergeant major screaming at you to push out another rep. But rest assured, it’ll be manageable and safe, regardless of your fitness level.