Often in a training plan (or during coaching), you’re instructed to go “hard”. For most, “hard” means as close to all-out as you can go for the designated length of the interval (9/10 RPE or 85+% of your maximum heart rate). It is important to note, however, that your hard can vary significantly depending on the day. If your body is worn down or you’re having an off day, you must train based on your perceived exertion. Just because hard equalled a seven-minute-mile last week, doesn’t mean that your results will always be the same.
In other words, don’t beat yourself up if you need to alter your perception based on how you feel at any given moment. Do push yourself, but know that every training session is different. If your mind says slow down or quit, ignore it- if your body does, be sure to listen!