+1 on the ice massage. At first it hurts!!! It gets better, and does help the tendinitis.
I'm sure you saw the link that Zen provided- your tensor fasciae latae is a small muscle that feeds into a broad sheet of connective tissue (iliotibial band) that runs down the outside of your leg and attaches below your knee. The function of this structure is to stabilize your leg and prevent excessive inward movement of your knee. Your glutes do the same thing, among other actions. If you are having pain or inflammation, you probably need to a.) stretch the iliotibial band, hip flexors, glutes, calves and hamstrings b.) strengthen your glutes and TFL and c.) assess whether you overpronate when you walk or pedal.
Lactic acid does not cause tendonitis. Overuse, inflexibility, and/or imperfect biomechanics are more likely causes. Massage, heat, and ice are good short-term solutions to manage pain but in the long term, the usual answer applies- stretch & strengthen! Good luck- I've dealt pretty successfully with IT band issues, but it takes some patience!
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