Soreness greater than 3 out of 10 suggests caution for training the same muscle group, and soreness greater than 6 out of 10 indicates it should not be trained.

“the kind of rule thumb we use is is like three out of 10 in terms of soreness if you're more than three out of 10 in terms of soreness we're going to start asking questions if you're higher than six out of 10 we're probably not training”