Referenced paper at [0] has annoying copy-paste protection. Key aspects of mouse exercise considered "maximal contractions" are:

Anaesthetised mice.

Electro stimulus of sciatic nerve to induce contractions.

10 sets of 6 contractions, each contraction sustained for 3 seconds, 10 seconds rest after each contraction (rest between sets not described).

Mice allowed to recover in a cage with water but without any food, this is thought to progressively increase activation of mTOR signalling.

Result: hench mice.

[0] https://physoc.onlinelibrary.wiley.com/doi/epdf/10.1113/JP27...