Re: Aikido Strengtheing
Just a good and simple (wrist) strengthening, you can nearly do wherever you want:
Just use the wrist warming exercises - nikyo undo, sankyo undo, kotegaeshi undo or just hold one wrist with the other hand and actively twist it (the other hand just resists.
Many dojo do it as joint warming to avoid injuries, so only one hand is active, the other one is passive and relaxed.
If you just use strength and resist as far as you do not harm yourself, it is a good strengthening exercise.
I do not know, if this was in Saotome'S book " Aikido and the harmony of nature", but therre you will find others, mostly paired exercises.