Question - Something I've struggled with figuring out in my series is how much training can one take in a day and how can you know when you're reaching your limit? Can you take a break and come back to it later that day or is that not how it works? I think it may have to do with the brain elasticity you mentioned in a video we did but I'm not sure.   

It's especially applicable to me because my day job takes up the majority of my week and so I frequently find myself wanting to grind out hours of mons on the weekend but have noticed I stall out mentally sooner than I'd prefer. 

How can I improve my training endurance? What tricks are there to being able to train longer but still efficiently (not making bad habits thru fatigue) from a psychology / learning standpoint?