Can I still train on aching muscles?

We've all experienced muscle soreness in the days after a workout, but what happens when you have another workout scheduled and you're still aching from the last? 

The decision of whether to train on aching muscles should be an informed but instinctive decision. For example, you might want to consider it a spectrum and then also cross-index that against what is coming up over the course of the next few days.

If you're suffering moderate aches, then it's worth considering your workout for the day, and the level of recovery you will be able to have for the next few days. For example, say it's Thursday, you might choose to go ahead with your Friday workout, pushing it a bit, but knowing in the back of your mind you have the weekend off.

Likewise, there is no harm in adjusting your workouts if a specific part of your body is aching. For example, if I'm aching from a chest workout but have a boxing day scheduled, I might pull out of the boxing workout because the same muscles are being used, and do a leg workout instead.

Sometimes you'll feel the ache, but once you've warmed up you will be good to go, but at the extreme, if you are very much aching and don't have your full range of motion, I wouldn't train. You won't directly damage your muscles, but the harm would come either from driving yourself into fatigue. or working tired muscles through movements that need full ability. 

That isn't to say that you can't keep active if you choose to miss a workout, and you can instead try to double down on your Steady State Cardio.