Answer: It Depends.
I get this question all the time about working out through muscle soreness and the answer is that it depends.
Depends on how sore your muscles really are, depends on what you’re planning on doing in the gym while you feel this sore. For example are you going to attempt to train the same muscle group again and how intensely are you going to workout? Are you going back for a light low impact cardio session or are you going back for another round of heavy weights?
It also depends on how well trained you already are. For example, are you sore because you’ve just lifted weights for the first time in your life, or you just took a couple months off of working out and you just got back into it? Or have you been going regularly and just pushed it really hard this time?
Right off the top I’d say if you’re a newbie and you’re really sore you likely want to avoid training the really sore muscles until they’ve healed to a point where you can move them without it hurting.
If you’ve been training for a long time and you’re accustomed to what muscle soreness is then you can decide how bad it is on a scale of 1-10. If it’s more like a 8 or a 9 then you should probably wait until it feels more like a 4-5 before you start training those same muscles again.
Range of Motion Test:
The other more objective way to determine if you’re too sore to train is to test your range of motion. If the soreness is so bad that you cannot perform specific workout movements with the correct form then you’re not ready yet. In other words, if you’re legs are so sore that you cannot perform a squat in proper form or you can’t really walk normally no matter how much you warm up then you should take another day off until the soreness lessens.
If your range of motion seems fine you can also test your strength. Warm up as you usually would on the sore muscle and test to see if you can handle your regular weights for a given exercise and rep range. If you can’t perform the required number of reps in good form without either failing or generating an abnormal level of burn/pain/soreness then you’re likely not ready yet.
To be clear, these are guidelines for determining if you can train the sore muscles, you can still train other muscle groups that are not sore.
As you can see there isn’t a perfect answer or a specific way to know 100% for sure if you can work a sore muscle or not. Experienced lifters who’ve been really sore and attempted to work through it will likely know where their limit is and can draw from this memory and self evaluate where they are on the soreness scale.
It may just be that you have to get all the way to maximum soreness and attempt to work through it and find out where the true limit is and work back from there. It won’t take long for you to learn what 10 out of 10 soreness is, and how to feel your way to an acceptable level that you can work through.
This exercise of finding your limit isn’t exactly comfortable, but you really only need to do it once to know for sure where the limit really is and when it feels ok to get back to training that same muscle group. After all, if you’ve never pushed it hard enough to experience your 10 out of 10 soreness, how would you know what 4 out of 10 is?
As a final note, it’s ok to train a sore muscle, as long as you can complete all reps of your given exercise in good form through the full range of motion. If strength or range of motion is compromised then you’re not ready yet. These two factors should always be your final guide above all else.