Rate of perceived exertion (RPE) is a reliable tool for approximating Zone 2 output, especially for individuals who are very out of shape or have type 2 diabetes.

“I think the most important you know tool for for virtually anybody is is rate of perceived exertion I think that will almost never let you down um in fact I would argue that for a really really out of shape individual rate of perceived exertion is even better than lactate and the reason for that is you take somebody who's got for example type 2 diabetes their resting lactate may already be at two so in those patients we actually never use lactate until you get somebody to a certain level of Fitness we only use rate of perceived exertion and we will provide heart rate guidance”