Mr Z
An AI Coach for Body Recomposition
Francesco Zen, founder of ZTraining · Last updated 19 June 2026
Why the threshold matters
Below that point, the body can draw on stored fat to fuel new muscle efficiently. Above it, the same approach is slower and less reliable, which is why Mr Z reads this before recommending it.
What happens from there
Once recomposition is the right fit, calories stay fixed while performance and training output improve. Over time, as your output increases, a real caloric deficit forms naturally, rather than being forced from day one.
Related: Can you build muscle and lose fat at the same time? · Body-fat threshold rules for building muscle
He built Mr Z, an AI coach trained on his methodology to bring the same approach to a wider audience.