Despite all of the safety practices and protective gear, you are still taking a risk every time you walk into a construction site in Minnesota. Accidents happen, and they happen more to those who are already injured in some way. This is why, if you were unfortunate enough to get an injury at work, you would probably want to be in top form before you returned to the job.
Like it or not, the doctor in charge of your rehabilitation might want you back in the workforce before you feel you are completely ready. There could be a number of options available to you at this point, but it would probably not be in your best interest to simply refuse to perform your assigned duties. This is typically true even if you feel discomfort performing your reduced duties — but it would typically be advisable to discuss this pain with your doctor as soon as the symptoms arise.
One of the reasons that you would want to comply with your new assignment is that your injury benefits could be affected if you do not. Your workers' compensation could depend on your relationship with your employer, as could any disability payments you receive. Causing a break in that relationship by failing to show up for your shifts could cause unwanted complications in your case.
On the other side of the coin, you might make an effort to return to work only to find that your employer has no appropriate positions to offer you. As explained in this article from FindLaw, your company would not have to create a light-duty job for you. It would, however, have to offer you the opportunity to fill light-duty vacancies if you were disabled, in certain cases. The issue is complicated, so please do not read this as legal advice. It is meant only to educate.