I'm in good aerobic shape but never did strength training. Yesterday, I did some basic strength work, using both dumbbells and machines. Nothing too crazy - I started light and built my way up. I feel fine today, with a moderate soreness. But, the one heavy pain I have is that I can't straighten my arms. I felt this immediately after working out, and it's only gotten worse. I feel pain on the inside of my arm (opposite my elbow), even if my arm is relaxed, and if I try to straighten it, it gets very intense.
I warmed up and cooled down aerobically, but didn't do any real stretching.
What causes this? Does it have to do with machines versus dums? What should I do to avoid this next time?