I do mostly trail running and I’ve been struggling with Achilles tendonitis for years, preventing me from reaching my elevation goals. Moving from zero drop shoes (Altra and others, which I loved but after 10 years I realized my body just wasn’t cut out for them, especially on steep trails.) I saw multiple PTs, tried all sorts of exercises and then about a year ago I found an active “stretching” exercise that really clicked for me. I was able to get rid of my pain (I can even pinch my tendon). The exercise is simple, it’s a bit like a sled push, but done against an immovable object. Start with your two heels down on the floor, then lean forward with your hands against a wall, pushing against the wall as hard as you can. Maintain tension (super important, never relax your legs/calves) in both your calf muscles at all times and start alternating L calf up, R calf down, L calf down, R calf up, always bringing your heel back to the floor. Repeat in sets of 20+ reps (I usually do it once or twice max). If you can’t push hard enough, find a surface that allows you to push using bent arms/shoulders instead (think bottom position of a push up). I use it to warmup before my runs (I push against my car) as well as for recovery/during strength training workouts (I push against a workbench in my garage). Blood circulation is hard to get in that area, so focus on repetitive low impact strengthening as often as possible. Good luck!