You shouldn’t feel exhausted after every workout. In fact, if you do, then you’re very likely to be overtraining.
Although, it might seem obvious, “if you need to ask “Am I working hard enough?”, the answer is likely “no”.”
This article, from Polar.com explains that there are signs that our training has been hard and we’ve really pushed ourselves as far as we can. A regular diet of consistent high-intensity (HIIT) workouts with little break is more damaging than a progressive workout program (also known as a mesocycle) with intensity peaks and rest periods.
The following article discusses how we need to have periods of low-intensity (slow or easy runs are an example) so that we can get our bodies to the next level during a challenging workout.Also the author provides 5 signs one can monitor to tell if you’re actually working hard enough via5 Telltale Signs You’re Not Working Out Hard Enough