The key to avoiding a repetitive stress injury is to take ample breaks to stretch your limbs. For example, if you type for hours on end, you should stretch your hands and arms for a few minutes every hour.
You should also make sure that you are performing tasks in the correct position. This might mean setting up an ergonomic workstation if you work on a computer or learning how to perform tasks (like lifting) safely using your legs.
Workers also might need time off from work after overusing a limb. Small aches and pains might disappear if given adequate rest. However, if you continue working, then they can worsen rapidly and lead to missed time from work.