Why I like to teach Kipping Pullups to my CrossFit Athletes Part-2.

 

Correlation vs Causality

I decided to start this post with this piece from the last one, because I think this is worth repeating.   Correlation is not causality is a basic principle of statistics. Simply because someone who "kips" has a shoulder injury does not necessarily prove that kipping is the cause of the injury.

Tarzan Knows Best

When I was younger we would watch Tarzan movies and try to emulate Johnny Weissmuller, who with his sidekick Cheeta was swinging through the jungles, jumping from vine to vine and tree limb to tree limb, bringing jungle justice to nasty white hunters and other bad guys.

Back in the day these costumes were pretty racey.

At this time I was growing up in Rockaway, New York, a peninsula with the Atlantic ocean on one side and Jamaica bay on the other. We had a base ball field by our house--actually we lived in the projects, but that's another story--that had two diamonds. The ball field diamonds had a huge chain link fence backstop that we hung a rope off of. We would climb in the inside of the backstop, pushing our fingers and Converse Chuck Taylors--high tops, thank you--through the chain link. One of our friends would hold a rope that we had hung from the front of the back stop for us to jump on to and swing out and then back into the stop, all the while doing our best Tarzan yell.
 

The rope hung from the outer edge of the back stop.

I'm not recalling this to take you on a trip down memory lane, but to highlight that hanging from our arms is a natural movement for primates, which we are. We're primates

As primates we are completely adapted to hanging from our arms, and it doesn't depend on rotator cuff strength.

Adapted to Hanging Out

 

Hanging out in the Hood.

 Animals that hang or climb trees as well as those that dig, have developed a "bone spur" within the Subclavian muscle that we call a Clavicle. The subclavian muscle runs from the acromian process to the sternum, the clavicle sits within this muscle's facial sheath. The acromian process acts like a roof or a stop over the top of the glenoid fossa--the "socket" on the scapula that the humerus sits in--which allows us primates to hang our body weight from our arms without dis-locating it.
(Unfortunately there is no such shelf on the under side of the glenoid fossa preventing our arm from slipping out when we bear weigh overhead. This is the job of the rotator cuff. More on that in a later
post.)

 There are three main muscles that we use to hang from our arms: the Lattisimus Dorsi (lat), aka the "swimmers muscle", the Pectoralis Major (pec) and the Middle Trapezius (trap).  (For a fascinating view into the body's fascial connections my friend and fellow Rolfer Tom Myer's book Anatomy Trains is a must read.)

The pec attaches from the sternum to the clavicle and the humerus, effectively suspending the front of the body from the upper arm.

The pec attaches to the clavicle and humerus.

(In this photo you can see the massive latissimus dorsi between the upper arm and the rib cage. It makes a lot more sense to use this muscle for a pullup than it does to use the smaller muscle around the arm's attachment to the scapula.)

The middle traps attach the scapula to the thorax.

The middle trapezius--diamond shaped--attaches the scapulae to the spine. When this powerful muscle contracts it stabilizes the spine and the scapula. This prevents the scapula from rotating or pivoting at the humeral head.

The lats attach the humerus to the pelvis.

The lat attaches the humerus to the pelvis through the Lumbar Aponeurosis a thick fascial sheet in the lower back--it looks white in this image--which effectively moves the pelvis towards the hand when the hand is fixed.
(In many people who are sedentary or don't do pullups correctly the lat is "turned off" in the sense of having actual conscious control over its activation.)
Pullups are initiated at the lat not the biceps. 

This combination of the lat, pec, traps and the acromion shelf allow us primates to hang out with little energy expenditure.

This is all great stuff, but what about the angular momentum that's generated by the kipping pullup and damage that can occur to the rotator cuff and labrum? Isn't this the problem of kipping? Or, is it the sign of something else?

That's the subject of  part 3.