When your muscle aches the day after a workout,  you have to immediately train that same muscle again

NOOOOOOOOO!!!! Never!

Muscle ache is an alarm signal your body sets out and is caused by tiny ruptures of muscle fiber and inflammations which have to heal first before you train that muscle again. You have to give each muscle 1-week rest before the next workout. Otherwise, you run the risk that the inflammation will grow, your pain could become chronic and you could develop a serious injury. Another thing that will happen when you exercise aching muscles is that you will definitely overtrain and even lose muscle mass.