Hey it’s Wasim and welcome to Curious Doc.
Today I’ll be answering the question of why it’s almost impossible to jump over
1.7m.
But to answer this, we’ll have to dive into the biomechanics behind how the human body
is able to generate the force to jump in the first place.
The Guinness world record for a box jump is set by Christopher Spell who box jumped 1.7m.
As you can see, he first crouches down quickly and then releases that energy explosively
like a spring.
There are a lot of interesting things happening here so lets have a closer look.
We might think a lot of the power is coming from his huge leg muscles like the quads and
the calves but actually the tendons that connect the muscle to the bone are just as important
if not more important in producing explosive power.
Let me explain.
In the first phase of the jump, called the countermovement or eccentric phase, the athlete
crouches down and the muscles and tendons stretch out.
After this is the transition phase, where the muscle contracts and pulls on the tendon.
This is a really important part of the jump because what’s happening is the muscle is
shortening and the tendon is lengthening but the total length of the muscle and tendon
unit does not change.
The tendon, which is stretchy and elastic, is acting like a rubber band and storing a
bunch of elastic potential energy.
This elastic potential energy is rapidly converted to kinetic energy in the concentric phase
of the jump where the athlete finally moves upwards.
Muscle contraction by itself is actually quite slow, so if you just had muscles attached
directly to bone, we’d probably lose around half of our jumping ability.
So tendons are super important to be able to store that energy and release it explosively.
Okay so we understand the role of tendons now but why do we naturally bounce down before
we jump up.
Doesn’t crouching down just waste energy?
Like why don’t we start from a squatting position and then jump up, since we’re still
storing elastic energy in the tendon, right?
That’s true, but it’s actually less effective because performing a countermovement first,
that is crouching down before jumping up, utilises something called the stretch shortening
cycle.
In fact, the countermovement jump in the average person is 10-20% higher than jumping from
a squatting position.
There are two reasons why the stretch-shortening cycle is so effective.
Firstly, there’s a mechanical reason.
If you jump from a squatting position, the tendon has time to stretch out and becomes
less stiff.
However, when we perform a countermovement, we’re pre-activating the muscles that stretch
out the tendons and increasing their stiffness.
For instance, when we bounce a mass on a spring we can see that the stiffer the spring, the
faster the mass bounces.
The same goes for tendons.
In fact, if we look at any elite athlete that jumps or sprints the research shows they have
really stiff tendons in the leg compared to the average population.
Okay so how can athletes improve their tendon stiffness and their muscle strength?
The answer is simply strength training with things like squats, deadlifts and calf raises.
Every time we do strength training, it causes damage to the tendons and when it rebuilds,
it rebuilds thicker and stronger.
There’s also really good evidence that the connective tissue between and around the muscle
fibers are also thickened with strength training so it’s not only stiffness of the tendons
that matter it’s the stiffness of the muscles that increase too.
Side note, the main reason we feel less soreness in our muscles after working out repeatedly
is because the connective tissue in the muscle remodel to become stronger even after just
one training session.
Anyway, as we can see, stiffening our muscles and tendons through strength training allows
us to generate more power through the mechanical effects of the stretch shortening cycle.
The second reason the stretch shortening cycle is so strong is because of the neurological
effects.
When a muscle stretches, we have special receptors called muscle spindles which detect the stretch.
These muscle spindles send a signal to the spinal cord which in turn causes motor neurons
to fire.
The motor neurons cause the muscle to contract to counteract the stretch.
This is called a stretch reflex and is the reason why the patella reflex happens.
Hitting the patella tendon causes the quad muscles to stretch, which triggers a reflex
for it to contract.
The stretch reflex is also really important in maintaining our balance when we’re standing
upright.
And it doesn’t stop there.
There’s another receptor in our muscles called the golgi tendon organ, which also
senses stretch but performs the opposite function to the stretch reflex.
When the golgi tendon detects stretch it will cause the muscle to relax instead of contract
thereby preventing tension in the muscles and tendons from getting too high and causing
injury.
So the stretch reflex helps us jump higher whereas the golgi tendon reflex does the opposite.
This is relevant because the second way an athlete can improve their vertical jump is
to do plyometric exercises.
Plyometric exercises are basically jumping exercises which have been shown to inhibit
the golgi tendon reflex and allow the stretch reflex to exert more force when we jump.
Unfortunately all these systems have a limit.
Our tendons can only become so stiff with strength training and our golgi tendons can
only become so inhibited with plyometrics.
And that’s why it’s so difficult for athletes to jump over 1.7m.
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Cheers.