What not to do when playing in colder weather and your hamstrings are feeling a little tight... about two weeks ago I was playing at night in about 40 degree weather. I didn't warm up that much and at one point I lunged for a wide, low shot and strained my lower back. Didn't seem like much at the time, but then about 2 hrs after I finished playing my back started to serious hurt. Next day. worse pain. Two weeks later, after some physical therapy, it still aches a little bit, but I'm finally able to run faster now and swing and serve harder.