I've been running about 2-3 times per week for the last 8 months, but recently I started getting a sharp stabbing pain in the back of my left thigh. Its frequency is intermittent, and occurs in all situations(e.g., reclining, driving the car, etc.) Last night when I started running, it started up but subsided after a bit (without any conscious adjustment.) However, when I was watching TV later on that night it started up again. Does this sound like a hamstring injury, or something else? Thanks for the input!
A portion of the muscle is probably starving for circulation, which is why many sedentary activities set it off. The circulation of exercise seems to help, but it is more important to know why the problem exists.
In 8 months of running, there has been enough time to develop tightness in the hamstrings and in some cases, actual injury. I'm more in favor of tightness and spasm, which can be quite painful, and would probably respond better to exercise than a tear or "pull."
Resting activities, however, are much more tricky. Sitting or laying with knees bent can shorten the muscle and aggravate the problem. Car seats can pinch off circulation in athletic hamstrings, just when they need more breathing room.
I often approach my own hamstring soreness with self-massage in a chair, by lifting the leg slightly, cupping both hands under, and sinking the fingertips into the rear thigh to probe for sore spots. A basic muscle flush would glide from knee to butt, and encourages lymphatic flow. This can also be accomplished with soaped fingers by lifting the leg slightly in the shower.
Ease up on your running a bit, and let the hamstrings heal, with a bit of help as described above.
You'll bounce back within a few days to weeks, and good luck!