Alpha Warrior: "Monster Barrels" obstacle
This was the beginning or my Alpha Warrior run. Believe it or not, I injured my shoulder 10 seconds in. I made it through the whole course, but the pain gradually got worse as I went along. Only prevented me from doing one of the 16 obstacles.
What happened was as I jumped off the first barrel, I left my right arm on top of the barrel, so when I hit the ground I wound up hyper-extending my shoulder a bit. By the end of the day my shoulder couldn't bear any weight and I couldn't lift my arm above my head.