How Many Rest Days Should I Take?
You must not base the amount of Rest Days you take just on muscle soreness alone, but on Central Nervous System Recovery as well. Muscle pain such as DOMs (Delayed onset muscle soreness) really becomes a problem only if it impairs the proper movement and contraction of the muscle - or if it's simply too painful to move throughout its full range. However, the Nervous System is more silent then say, muscle soreness. With muscle soreness you know that the muscle has been worked so much that micro tears of the muscle fibre have occurred and they are in need of repair - something that your Nervous System Fatigue is not directly linked too. Your Nervous system, the system which tells your muscles to turn off + on can still be fatigued even if you do not create enough micro tears to solicit muscle soreness after your workout. Generally, if it's too fatigued it will only manifest itself subtly, with slight decreases in strength and moderate decreases in focus and concentration. These things are much harder to identify and link to poor Recovery.
NOTE: The information given here refers to a split bodybuilding routine.
1. Individualise Your Training Split
If you are a beginner, great! You must adhere to a strict structure of training so you learn and adapt quickly to the exercises and routines, and it might not be time to individualise things just yet. However, if you've been training for 1 or more years already then you can be more methodical about your training split. Just because everyone trains Chest on Monday doesn't mean it has any relevance to how your body recovers. If you aren't ready to train Chest then Training it will not help you, and with prolonged Nervous System Fatigue you might end up going backwards with your training. Conversely, if you're ready to train earlier then there is no need to wait until Monday. Shape your training split to your individual needs.
2. Do Not Be Afraid of Resting
Resting is when your muscles grow and adapt. Training only solicits adaptive potential, it does not manifest it. So ask yourself, do you want to spend more time Training or more time Resting? Everyone who is comfortable with their ability to solicit adaptions from their training wants to take more and more Rest days - why? Because they know that all their hard work is paying off the better their Recovery is! We do not hibernate for 6-8 hours every night for fun do we, as we would still need sleep regardless of training - SO with the added stimulation of micro tears and Central Nervous System Fatigue our Rest becomes even more necessary and welcome.