Posted in Blog.
Put Some Spring in Your Step
NBA GM’s call it “springy,” NFL scouts call it “twitchy,” while running coaches have dubbed it “efficient.” All these terms are used to describe an often under-studied and under-trained aspect of sports performance/pre-hab that may also be the single most important. Science calls it the concept of the stretch-shortening cycle.
As a young basketball player I used to hammer away at squats and deadlifts, thinking that in order to jump higher, I needed to strengthen my legs as much as possible. It was only after watching a video of LeBron James struggling to squat about half the weight I was using did I realize that I might be a little off on what went into jumping (and running and cutting too). I still wasn’t able to dunk and he was throwing down from the free-throw line with ease. So what gives? Shouldn’t it be that the stronger a muscle is, the faster and more forceful it can contract, and the faster you can then propel yourself? The more this question is researched, the more we find that the answer is no.
Instead, in order to generate huge amounts of force, humans use the viscoelastic properties of muscle and tendon to our advantage. These structures are stretchy, and luckily for us, the more (and the faster) they stretch, the more force they generate as they recoil to their original length. Think about the slingshot you got in trouble with as a kid. The further back you pulled the sling, the further the object in the sling went. Muscles and tendons function in this exact same way. What’s more, the elastic energy generated by this phenomenon is “free,” meaning our body does not have to generate ATP (our energy currency) to create it, and it does not contribute to fatigue. This is the reason running coaches describe athletes who use it well as “efficient.” And like all other properties of our musculoskeletal system, this stretch-shortening cycle can be trained.
The examples are everywhere: top tennis players who rotate, side-bend, and extend their trunk as much as possible to load (stretch) their muscles before serving a ball 130mph. PGA tour athletes who drive the furthest are also the ones with the biggest backswings to maximally load their trunk, hips, and shoulders. Soccer players who bring their legs backward an ungodly amount before firing off blistering shots on goal.
But how does this affect running? You have probably heard the term “over-stride.” Nothing is a greater killer to your ability to generate elastic energy. If, while running, you land with your foot way out in front of your body, your leg then spends its time absorbing the shock of landing before it even things about loading its metaphorical springs in the achilles, quad, and glute. Instead, by landing with your foot closer to your center of mass, your body goes straight into the loading phase, meaning you get through the stretch-shortening cycle faster, and thus produce more elastic “free” energy.
The concept is also why if you walk into any top PT clinic or performance space, you won’t see people hammering away at clam shells to try and “turn on” their sleepy glutes while running. You will instead see people learning how to properly load their glutes by getting the correct amount of stretch, which will allow it to function correctly during running. Rehabbing dysfunctional muscles is rarely just about stretching and strengthening that muscle, it’s much more important to learn movement patterns that can facilitate the dysfunctional muscles because without learning how to load muscle correctly during a given movement, you are bound to end up with dysfunction somewhere.