I have l5 nerve root compression and a lot of twitching in legs and feet. i have noticed when i do activity (walk/bike/exercise) my twitching gets a lot worse for the hour or so after the activity. why is this?

Rarely, the nerve root compression affects both lower extremities equally. You should see a neurologist for a thorough evaluation.

The twitching is due to fasciculations of the muscle, which occur when a weakened muscle exceeds it's endurance capabilities. Furthermore, poor sleep and caffeine can accentuate them. The weakened muscles could be from a pinched nerve. You should be evaluated by a PM&R Doc or neurologist for further clarification.