While not exactly a touchscreen, I spent many hours/days/weeks/months programming and using an HP 9845C back in the 1980s. It had a series of 8 soft-keys built into the lower edge of the display that could be controlled via software to display menu options and generate interrupts when pressed. Users of our software (and that of many others) used these soft-keys extensively to navigate information. Users also switched regularly back to the keyboard to enter queries, etc.
While I do remember some arm tiredness, the rapid dance of fingers across the soft-keys was so efficient for navigation that everyone loved the system. It might be worth reflecting on the details of this design. For example, the user could rest the hand on the display frame or the body of the computer without straying too far from the soft-keys; all of the "touchscreen" actions were at the lower edge of the display. Both of these features decreased arm strain.
FWIW, some applications on this machine used light-pens, which also required a touchscreen-like mechanic It might be worth exploring what use cases found these awkward devices to be wins. I notice that the Wikipedia article on light-pens claims Gorilla-arm led to the demise of light-pens, but without citation.