I went out running for the first time last week and the day after I had really sore Achilles tendons, continuing for two days total. I ran about 5 miles (4.84 exactly, according to the route I mapped out) and only stopped two times. My aerobic capacity is decent and the only reason I stopped was because traffic.

I've done sprints before and never had this problem, up to 3x a week with one day a week being maximum exertion across all phases of the Sprint for up to 200 meters, and I still never had sore Achilles. I strike slightly behind the ball of my foot when running and right on it when sprinting. My strike point is in line with my knee and I lean slightly into it with my hips with my spine neutral when I run for distance. I ran a short distance to evaluate what technique was comfortable for me at that speed and I liked that.

My question is, why is my Achilles so damn sore? Wouldn't the sprints be harder on it? I have the aerobic capacity to run that same route no problem every day. I did it again yesterday and am feeling tightness in my Achilles. Is it technique? Overuse? Should I drop running and stick to sprinting and farmer's walks for gpp & fat loss?