My dad had a knot on the inner part of his arm about the size of a golfball. He was driving home from work and had a huge cramp in his arm. He went home and rotated ice and heat on it. Woke up the next day with big bruises on his arm where the cramp was with a knot about the size of a gumball. The knot is still sore to the touch. And it hurts to do any heavy work with the arm. The bruising has been their for several days. Should he be concerned or see a doctor? o and FYI he uses this arm to swing a hammer. has been doing this for over 10 years, and this is the first incident. Before the cramp in the arm he had a bad cramp in his back that took his breath away and made him swore for a day.