Why Can't I Jump High? The Science Behind Vertical Leap

Ever wondered why you can't jump as well as your teammates? or why some people are just naturally bouncy? The answer is probably somewhere in here...

When it comes to any physical performance it can be broken down into four factors.

  1. Energetics: How the energy system and the creation of ATP. Energetics are the major site for fatigue across most time spans.
  2. Biomechanics; These are the relationship between joint angles and limb lengths. This is particularly dictated by movement skill and coordination
  3. Physics: The influence of forces on the body, things like gravity, inertia, momentum and mass. 
  4. Physiology: The muscles, tendons, and nervous system that are responsible for creating movement and force.
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Energetics

When it comes to vertical, we're looking at a tiny amount time, even with a run up it's not going to be much more than 3-5 seconds worth of work. During such a short amount of effort (even as intense as a max effort jump), Your muscles aren't going to be going much beyond your ATP stores and maybe dipping into your Phosphocreatine reserves.

As far as a limitation to your jump height? there's not much going on here. For a single jump your energetics are not much different to Lebron James or any Olympic high jumper. With repeat jumps, though, that’s a whole other story.

Biomechanics

Okay, number two, with biomechanics, there is kind of two really key factors that influence jump height.

1) Arm swing

Arm swing is such a big deal, not just on the way up but also on the way down. Your arms on the way down help load the legs like springs and on the way up, they help accelerate your torso upwards allowing the legs to do their thing pushing hard into the ground. 

2) Joint sequencing

That’s your ability to coil the legs tight like a spring and then uncoil it in the proper order. When you start the up phase of the jump your joints should open in order from top to bottom; Arms > Hips > Knees > Ankles. This maximises the amount of time you can push into the ground and increases speed at take off by unloading the legs faster (more on these in the physics section)

Now, both arm swing and joint sequencing (sometimes called segmental sequencing) are about enhancing the efficiency of the stretch shortening cycle.

A bad jumper looks like this.

 
Stretch shortening cycle bad
 

The eccentric portion is slow and during the amortization, there is a lag which leads to lost energy.

Now, if you are a more explosive, reactive, stronger athlete, a better jumper, they look more like this:

 
 

This athlete going to be able to load that eccentric portion more aggressively and faster (their legs are more spring-like), and then turn around the amortization phase quicker, meaning none of that eccentric loading you get out of the bottom, the amortization phase faster and it will create more concentric power taking more of that eccentric load with you skyward.

Physics

Physics is all about the ability to accelerate the body vertically, displacing the center of mass. To do that, you really have to beat gravity, kind of.

Gravity has a speed of 9.8 meters per second per second (it's a squared relationship which means it is an acceleration). To become airborne you can leave the ground at any speed which is why everyone can jump, a little. You don’t have to beat gravity completely (thanks Davey). But the greater your speed at take-off the higher you will jump.

If you leave the ground at 9.8m/s/s, you're going to be moving vertically for one second before you reach 0m/s speed (due to gravity bringing you back down).

So, the faster you leave the ground, the longer you'll beat gravity for and because it’s a squared relationship every millimeter of take-off speed counts.

If you double your take-off speed, you'll jump up four times longer.

if you triple it, you jump nine times as high.

And because you’ll be moving upwards for longer and you’ll jump higher in a squared fashion as well.

Physiology

To achieve more velocity at take-off, we need to look at the physiology, the internal happenings of our body that will maximise our ability to produce force and do it fast.

1) Speed

Speed begins quite literally with how fast you can create contraction within the muscle fibers, faster contraction then creates greater rotation of the limb or body segment around the joint (known as torque), put this velocity in the right sequence and in the right direction and the entire body will, therefore, move faster.

2) Strength

Because jumping requires moving your body mass and bodies are reasonably heavy it's not good being able to move our limbs fast if they can't also create the required force to displace the center of mass and break the Earth's hold on us.  

Speed x Strength = Power. Power is the key to success in almost every sport

A number of factors contribute to strength and the good news is the majority of them are directly in our control.

  1. Muscle fiber type ratios. We all have a genetic baseline (which is a big factor in most athletic endevours) but you can shift your fibers more readily than most people think. The old train fast to be fast is pretty accurate, we do this via our hybrid fibers which are highly adaptable and can be manipultaed to serve our chosen event or sport through our training mode.
  2. Downregulation of Golgi Tendon Organs. These guys are the rate limiters in our tendons that control the amount of force you can or can't produce as a way of protecting you from hurting yourself. One of the cool ways strength training works is by telling these little organs that it's OK to create force and that they can chill out.
  3. Increased neural drive. That is a software upgrade for your body. If you can make your brain and your nervous system better at talking to and controlling your muscles we become more explosive and you're going to jump higher. One of the best ways to do this is through the principle of intent to move.
  4. Add cross-sectional area (CSA) to your muscles. A bigger muscle can ultimately create more force, but bigger muscles also have the drawback of dragging you back down to the ground. There is a body weight sweet spot; enough muscle to create enough force, but not so much that it slows your take off or becomes a liability once you get airborne.
    Lighter, leaner people tend to jump higher because they can create more velocity and more force relative to their body weight, So, you can be as strong as a truck, but if you're also as slow as a truck, that's going to make it hard to leave the ground.

3) Flexibility & Mobility

You can create all the force you want, all the speed you want, but if your joints do not have the range to be loaded like springs eccentrically then uncoil and explode into triple extension, all that force will be for nothing because you can’t successfully transfer it through the bodies segments and into the ground. The more range you can take your muscles and your joints through, the more they work like springs because they can be loaded tighter and give you more recoil on the concentric phase. Foam rolling and stretching are your best weapons for this.

4) Tendon reactivity & stiffness

While supple pliable muscles are beneficial for storing energy, tendons should be the exact opposite.

For every bit of flexibility and mobility your muscles and joints need to have, tendons should have the opposite quality of what is called stiffness (stiffness is a horrible word, reactivity kind of fits as well). When your muscles contract and pull on the tendons, your tendons should resist moving as much as possible relative to its original shape.

That tendon stiffness directly links back into your stretch shortening cycle. Improving this tendon reactivity and stiffness is improved through strength training, plyometrics and jump practice

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