I find myself speaking about this to athletes everyday! I cannot emphasise enough, the importance of a Rest Day!!
Rest is as important as your training and should never be negotiated. Some workouts should be easy and some hard, it is essential to rest but many athletes still over train and feel guilty when they need to take a day off BUT the body requires this in order to repair and strengthen itself..
Workouts are supposed to have variation, stressing the body on full pace will only result in burnout or injury as you are not teaching your body the difference between fast and slow pace when needed, or making allowance for rest and recovery. If the same thing is done over and over the same result occurs season after season, it’s that simple.
Continuous training can actually weaken the strongest athletes so rest days are critical for growth and too few rest or recovery days can lead to “over training syndrome” which is a very difficult condition to recover from, and can put athletes out for a very long time.
What goes up must come down. To recover is to create growth and readiness for your next workout.