I have been digging for what seems like an eternity. I only manage an hour or so an evening, and about 3 to 4 evenings a week. I'm double digging my ground to ensure that I can improve the soil structure as much as possible (I have heavy clay), and I'm removing as much of the bindweed as I go as poss.
I have found that on evenings when I am unable to get down there to breakup the ground I dug the previous night, a good watering makes it more manageable the following day. I don't suffer with shoulders, but I do have a history of back problems so little an often seems to be kinder on me.

Happy digging