カッコに入る動詞の形を教えてください

this is not a piece of advice to you I'm talking to myself for my practice of writing skills.
I've tried to put your sentence into GT. GT's translation is the next sentence.
Because of the difficulty in maintaining concentration, some researchers recommend taking a short break from work about every 90 minutes.
please assess GT's translation. I suppose it'd be unnecessary to fill the blank.
if you feel any unclear then re-post the unclear point to this section.
:GT.
https://translate.google.co.jp/?hl=ja&sl=en&tl=ja&op=translate