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 didnt 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...
Perhaps the tendency of the program to favor exercises like ring dips, ring pushups, muscle-ups of the rings, and kipping pullups, without an adequate strength base, as well as overhead work like snatches, jerks, presses, and overhead squats, all of which is done for time and none of which is controlled for technique, would explain the problem better than "bad posture". The "muscle imbalance" that is critical would be the lack of strength in all the muscles that should control the glenohumeral/AC position that creates the impingement. The way to "balance" the muscles is to press, bench press, and chin until you're strong. All of these exercises are safe IF YOU'RE STRONG ENOUGH TO DO THEM CORRECTLY, but these people are taught that Elite athletes can do them, that They Are Elite because they joined the CF facility, and they are encouraged by inexperienced staff -- most of whom really need a personal trainer themselves -- to attempt these movements. There is no need to post video of form sacrificed for time, because we've all seen it already. People that try to do muscle-ups for weeks before they get one are people who are not strong enough to do muscle-ups. In this particular instance, if you try to cut in line there is a price to be paid. All it takes is one bad rep where the ring gets away from the shoulder, out to the side, to tear the cuff tendon.
1. Crossfit is not a novice program. In spite of the hype, it is not scalable to any ability level. It does not make people strong in any reasonable time frame.
2. No amount of devil-may-care bravado makes up for bad coaching
2. Ring Muscle Ups may not be worth the risk. My training partner somehow got his left arm in a hammerlock position on the rings (arm behind his back). I was sure he was going to dislocate his shoulder. Good thing his is strong and was able to maintain the position and extricate himself without hurting his arm or falling on his head. It was scary though. I'm really starting to prefer bar muscle-ups. They are IMO more functional anyway.