Stiffness and soreness in the morning with tendonitis occur because inflammation chemicals accumulate during rest.

“And what you always routinely say, which is really common if you're planner fascitis or patellar tendonitis, is when I first get up, it's really stiff and creaky and sore and hurts. And that's because tendons love blood flow. They love movement and they love motion. And so all those chemicals that come with inflammation, if we're just sitting around or sleeping, that's the opportunity to get stiff and really sore and achy.”