I would say that sometime back in 2015 or 2016 I purchased at auction two Intex swimming pools which I then re-sold. It was probably the worst purchase I ever made during my auction resale days due to the size and weight. These were inflatable pools in giant boxes which were VERY heavy. When one of the purchases came to pick up the pool, we proceeded to lift the box into the back of his truck. I took a Sumo Deadlift stance and hooked both hands under the box, and we both lifted. Normally this would not be an issue had it been a standard barbell because of the starting height of the bar. In this instance, however, I was lifting from a deficit, i.e. the box was on the ground. So, while I had been training at my local CrossFit gym for about 3 years, I hadn’t trained for this load in this position and thus, injury.
While lifting the box, with my hands in a supinated position (i.e. palms up like doing a barbell curl) rather than pronated like when doing a non-mixed-grip deadlift, I felt a pop in my upper right arm which was followed by a few months of pain. What I didn’t know at the time was that the pop was most likely the labrum tearing from the force on the long head of the bicep tendon.
I believe this moment is when the trouble began, and since, I have never fully addressed it. While over time it has seemed to heal, in fact, it is very unstable and as I’ve proven, vulnerable to additional injury through normal use.