The toughest jobs in the U.S. include firefighters, construction workers, and nurses. A poll of 2,000 employed adults found 21 percent believe working in mining or oil is one of the most gruelling jobs around, while 11 percent think being a doctor is a role only for the most resilient. Others feel that only the iron-willed could be a roofer (10 percent) or a teacher (eight percent). According to those polled, challenging jobs involve being on your feet all day (40 percent), working in all