Many people think that power is most important to execute a good nito strike. But as Imafuji sensei said: Women also practice nito ryu.
In my dojo I met a female sensei that also practices nito. She's smaller than me and she's not the strongest person. Please don't get me wrong, Idon't say that with disrespect, I'm not a bodybuilder myself!
Of course you need a basic level of arm strength to hold your daito above your head all the time, but you don't need much force to execute a strike.
The most important thing is the center of gravitation of your shinai! It's difficult to describe via Internet also because English is not my native language.
Please read the text about nito ryu at my dojos website, it's written in English and I can't tell you better at this point.
I will try to write down some points to use your daito with not much power another time.
Kendo-Guide.Com: Thank you for your post and sharing very valuable information with us.