For the past two weeks, I have had weird intermittent warm sensations in my upper and lower legs on both sides. The sensation is like there is a low-level heat source inside my muscles, and my skin is not warm to the touch. It is not burning or painful, just noticeably warm. I have recently begun an aggressive hiking program in advance of a 10-day backpacking trip this summer, and symptoms started after a particularly difficult hike - but I am in good shape, do cross-fit and endurance workouts regularly, and generally recover quickly from workouts.