Avoiding rotator cuff injury
A Crossfit Journal article that appeared recently is a cautionary tale for all lifters, detailing Tim Burke's progressive rotator cuff injury, surgery, and recovery.
A brief excerpt for purposes of commentary:
"Tightness in my shoulders and pectoral musculature was forcing a rounded shoulder, which in turn caused a winged scapula. Compounded with violent shoulder extension during lightweight muscle snatches, kipping pull-ups and overhead squats, the connective tissue broke down over time. Kelly explained that I needed to fix my posture in an attempt to balance out the musculature from anterior to posterior. He also said that if I didn’t fix the imbalance, the problem would keep surfacing again and again."
MRI showed a 75% tear in the supraspinatus tendon, which runs through the narrow space above the humeral head, has a 'poor' blood supply (i.e. slow healing) and is easily impinged. From an engineering perspective this is a classic failure mode just waiting to happen.
Connective tissue does not just "break down over time", it's either abraded, cut, or tensile strength exceeded in whole or in part. (Notable exceptions: antibiotics like Cipro are known to increase Achilles tendon ruptures, and anabolic steroids either make tendons more brittle or increase muscle strength disproportionately, both increasing chance of rupture.)
In this case it sounds to me like repeated mechanical impingement by wrong choice or form of exercises, and inadequate time left to heal. Muscular imbalances potentially compound the problem by further compromising form.
Impingement is serious, especially over time. Look at the mechanical design of the shoulder: impingement necessarily occurs at the same position of the tendon, so it's like pounding a dull knife onto the tendon over and over.
Also, reportedly, doing heavy overhead shoulder work after the tissues are engorged with blood, favors impingement, versus doing overhead stuff early in the workout.
Takeaway lesson: choose exercises, form, and recovery programming with care. Nothing disrupts progress so much as mechanical failure.
Put another way, "lifting to failure" shouldn't mean this kind of failure...