Recommendations for work in the heat suggest working to work-to-rest ratios depending on the work intensity and the extreme environment. These recommendations aim to prevent excessive core body temperature rise and dehydration but their usefulness to achieve these aims is unknown. Even less is known about the body’s responses to work in the heat among variations of work/rest cycles. Therefore, the purpose of this study is to determine whether these worker recommendations prevent excessive core body temperature rise and dehydration.