This particular query can’t be answered with a universally numerical conclusion. Many variables factor into how many days of rest one should have for optimal muscle building results. However, I will go over a few scenarios in hopes that it helps paint a clearer picture.
First of all, no matter what type of Health & Fitness Guru Blog you are reading from, the best knowledge comes from personal experience. Yeah, the stuff you have personally tried, tested and adjusted to your own genetic makeup.
While browsing through the Internet, I was surprised to see many of the health blogs saying the exact same answer, which was 24 to 48 hours of rest between workouts. Personally, I disagree. For one, what type of workout? How intense is it? Are you concentrating on certain muscle groups per each workout or are you taking the shotgun approach? How old are you? Are you a beginner just starting to workout or are you a professional bodybuilder building massive muscles? All of these things and many more factor into how many days of rest your muscles need for optimal growth and/or safe methods of building lean body mass.
The small groups of muscles like what are found in your forearms, for example, could be worked thoroughly almost daily while larger muscles like what are found in your chest, shoulders, hamstrings, etc., will most likely need more time to fully recover from a hard workout. Your genetic makeup, hormone levels, overall health, age, hours of daily sleep, and so on, all affect how quickly your body recovers.
I have heard of many professional bodybuilders training 6 days a week, with only one off day. But guess what? They only train certain groups of muscles once a week. Yep, so that means that they allow 7 days of rest per muscle group for building mass quantities of muscle. However, you can rest assured that they totally tear down each muscle group during those days of pumping iron/working out.
The other thing you need to do is simply listen to your own body. If you go back to the bench press and you still feel weak from a workout you did a couple days ago, wait a few more days before trying again. I try to wait an extra day or two after I feel ready for another intense weightlifting session. Always try to keep in mind, your muscles grow when you are resting, not when working ’em to the point of exhaustion.
With that being said, aerobic-style workouts don’t really need “days of rest” in between, but it never hurts to have a couple off days during the week, right? As for building muscle, lifting weights, intense training, etc., I like to take 6 to 7 days off between working that same muscle again. For optimal gains, even if I was in a big rush, I still wouldn’t want to take any less than 4 or 5 days off, but that’s just my opinion; cheers!