The Stretch-Shortening Cycle (SSC) is a fairly well-accepted theory in exercise science that has a boring definition of:
A stretch-shortening cycle (SSC) can be defined as an active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle.
In layman’s terms, it’s why you jump higher when you bend your knees immediately prior to leaping instead of starting in that lowered position. It’s why a push-up, pull-up, or squat is easier to do with a rebound instead of a dead stop. (Try squats from a dead stop with pins in the bottom of the rack set to below parallel if you want to hate your life, by the way.)
So, the SSC is certainly seen in practice, though the exact mechanism of how it works is not really understood to exercise scientists. (The effect of tendon viscoelastic stiffness on the dynamic performance of isometric muscle – 1991 Baratta, Solomonow) In baseball, the application of the SSC can be seen through these cues:
- Early and active hands in the hitting stance
- Scapular load to unload
- Leave the arm hanging down at footstrike
The last cue is something that I’d like to talk about. Without getting into the psuedoscience of the Inverted W that has dominated talk of baseball pitching injuries, there is this idea that the conservation of momentum principle applies with regards to the arm action of pitchers. A constantly-accelerated arm into shoulder external rotation / forearm layback, in theory, helps to engage the SSC by laying the arm back quickly and therefore will unload faster.
However, there is no evidence that links increased velocity of shoulder external rotation (vER) with increased ball velocity. The following articles conclude that the strongest markers leading to increased ball velocity were increased MER, faster pelvis and upper trunk rotational angular velocity, and greater landing knee extension and stabilization:
- Relationship of pelvis and upper torso kinematics to pitched baseball velocity. Journal of Applied Biomechanics (2001 Stodden, Fleisig, et al)
- Comparison of kinematic and temporal parameters between different pitch velocity groups (2001 Matsuo, Escamilla, et al)
- Relationship of Biomechanical Factors to Basebal Pitching Velocity: Within Pitcher Variation (2005 Stodden, Fleisig, et al)
However, a more internally rotated humerus (upper arm) at Stride Foot Contact (SFC) is linked with increased humeral torque (Humeral Torque in Professional Baseball Pitchers – 2004 Sabick, Torry, Kim, Hawkins), and a more internally rotated upper arm at SFC is a major coaching cue of how to increase vER.
Getting to the High-Cocked Position
The high-cocked position looks something like this:
For a period of time, pitching coaches were recommending that pitchers get to this position as soon as possible – doing something that might be called the “goalpost drill.” Paul Nyman railed against these theories and advocated an inverted arm action (see the Real Story Behind the Inverted W as well as my article, Why is it Called the Inverted W). Paul said: “Video of pitchers who threw hard do not ‘go to the high cocked position.'”
Like anything involving baseball pitching mechanics, the truth is not so absolute. Nate Jones (White Sox) is a perfect example of someone going to the high-cocked position immediately with very little artificially created vER through a concept of a flowing arm action that “conserves momentum.” And his velocity is… well… take a look at the upper left corner of this GIF:
Nate Jones also has very bad:
- “Connection” of the throwing arm
- Tempo to the plate
- Glove side action from a lens of “firmness”
What’s the bottom line about the SSC?
The bottom line is that it’s not so simple to understand such a complex system like throwing 95 MPH fastballs for strikes. There are significant doubts about understanding how the Stretch-Shortening Cycle even works in exercise science, so to rely on concepts like a “quick arm” in layback causing improved velocity are not necessarily accurate – and may increase the chance of suffering injuries in the pitching shoulder and elbow.