Ok heres the deal. Ive been lifting alot in the last few months, but since hockey season has gotten into full swing ive really neglected my legs. i want to get back into it and start squatting which i dint do before. the reason i never did it is because everytime id squat id do 10 reps with just the bar, then move up to 135lbs. when i did a set or two with the 135, id always pull something in my hamstrings, or atleast i would ruin the rest of my workout becuase it really ruined my leg for the day. Is this from a lack of warming up/stretching, or because i dont work my hamstrings enough?