There was a bit of chatter this year about shoulders “popping out” or dislocating at mountain biking’s premiere freeride event, Red Bull Rampage. There was one competitor whose shoulder popped out during a practice run after landing a drop that was small for his skill level. Another competitor was happy he made it down without his shoulder coming out during the competition. Naturally, shoulders popping out could have a grave consequence at this level, so what is happening here?
Force and acceleration
Part of the explanation lies in Sir Isaac Newton’s 3rd law of physics, for every action there is an equal and opposite reaction. In terms of Red Bull Rampage, the force of a bike hitting the ground when landing a drop is an action, and in an equal and opposite response, the ground, sends force into the bike and body of the rider. As a reminder if you haven’t taken physics recently, force is equal to mass x acceleration, and acceleration is equal to force divided by mass.
How a joint injury occurs
When landing a drop, force goes back up into the body and applies stress to joints through acceleration. If the muscles of the joint are functioning well enough to control the incoming acceleration, injury is unlikely. However, if that joint and the muscles that support it are functioning poorly and have lost (or never had) the ability to control the force of acceleration, injury is very likely to occur. This is true for most any injury from joint trauma. The force of acceleration into the joint is what creates an injury when that acceleration does not meet an opposing force capable of stopping it before injury may occur.
Muscle response time is key to controlling the force of acceleration into a joint. For instance, ACL tears result when the muscles that control the knee do not respond quickly enough to control the force when direction is suddenly changed. The resulting force is then asked to be controlled by the ACL, and if it is unable to decelerate those forces before being stretched beyond its capabilities, it ruptures. As one of the Red Bull Rampage competitors landed his bike after a small drop on a practice run, his shoulder dislocated. The muscles of his shoulder did not respond quickly enough, so the ligaments were asked to do the job of stabilization. They were unable, so it dislocated on him. Each time this rider lands a drop where the force of acceleration is greater than what his muscles can control, his ligaments are stretched with small tears in the deceleration process. Once the ligaments are stretched too far to control the shoulder, it dislocates. Hypothetically speaking, this is why I think a shoulder will come out easier and easier over time. Each time the shoulder is exposed to force, and the muscles are unable to control it, the job goes to the ligaments. This done repeatedly over time negatively affects the ligaments by weakening them. Then it starts to pop on on smaller and smaller hits.
What’s missed in rehabilitation
The usual path of rehabilitation is to strengthen the shoulder muscles. Unfortunately, this approach is ineffective to a large degree, especially at the professional level where strength is typically not an issue! In fact, the issue lies instead in muscle response time (which I call ‘delay’) and muscle recruitment. For example, if the competitor’s muscle response time in the shoulder is 1/20th or 1/30th of a second delayed in the time it takes to contract when he lands a drop, what happens to the force of acceleration upon landing? It charges into the ligaments at full power! As for the rider, hopefully when those muscles finally do contract they can decelerate the force before damage is done. To fully control the force of a landing, muscles must contract immediately.
Once delay is removed, the joint is able to withstand a greater accelerating force than before. The muscle responds quicker, and there is a higher level of muscle recruitment. This is a very important piece that (as far as I can tell) is missed in rehabilitation programs, leaving the athlete vulnerable to further injury and poorer performances.
Finally, the solution
My hypothesis is that those athletes at Red Bull Rampage have delay and poor muscle recruitment at the shoulder joints – made worse through one or more traumatic (crashes) shoulder dislocations. They are both very strong athletes, considered to be some of the best in the world at what they do, so strength is not an issue! Instead, the problem lies in the inability of the joint to handle the force of acceleration. This can only be addressed through removing the delay thereby increasing muscle recruitment and reducing the time it takes for the muscles to respond and contract. Once this has been taken care of, further injury to the ligaments will subside, allowing them to heal as the force into them is significantly reduced. Finally, the performance of the athlete will increase naturally as faster muscle reaction time leads to less fear of dislocation and more confidence in the endeavor.
Before and after videos of muscle firing delay reduction
The following 2 videos are sequences I use to address much of the shoulder delay. With delay in the firing of the muscle comes delay in the action of the board and the participant will have less control. As I remove the delay control is gained because the muscle groups are firing with less delay. Each video has a before and after segment showing how quickly the changes are made.
Thanks for reading,
Steve Noble, DC