Hey Camilla, I have pressed on both sides of muscletone and while it is certainly capable of handling the impression, I would caution you and trying to press too much into the paper. It definitely leaves a mark on the reverse, which is completely fine for a 1 sided piece, but can be troublesome for 2 sided.
In terms of what I personally use for a 2 sided impression, I generally default to Lettra 220# because you can get a deep impression on both sides while not making transferring too much on the reverse.
What are your thoughts on Muscletone and 2 sided impressions?