Overtraining means exercising harder than the body is capable of handling. When overtraining occurs, the muscles, bones, heart and lungs are worked too hard and can even be dangerous to one's health. Possible symptoms of overtraining include muscle tension, irritability, decreased appetite, increased aches and pains, and sore muscles. It is our responsibility when exercising to warm up properly to prepare the body and prevent injuries. Not warming up could lead to increased muscle soreness.