When I'm doing push-ups,
I always do them on the knees.
That's mainly because I'm bad at this exercise
and doing the full version seems impossibly difficult.
Does it mean that I just suck,
or is there a physical reason for this?
Does it really change a lot if we try to toughen up the exercise by raising our feet?
And assuming we are able to,
are faster push-ups more efficient than slower ones?
Do you feel the experiment coming?
We've already established that I can't do push-ups on my feet
so I asked Franck to be my guinea pig for this experiment
and be kind enough to do plenty of push-ups
while I watch him and acquire data.
We borrowed a Wii Fit from which we got some data about weight
thanks to a code written by the neuromechanics lab
of University of Colorado.
We'll be using the Wii Fit as a weighing scale
like the one you keep in your bathroom
except that we'll be able to monitor the weight change in real time.
The principle is simple:
Franck places his hands on the scale,
and from this we measure the force he needs to use in order to do a push-up.
The force we measure is the same as that which his body has to bear.
At this point I need to clarify something.
Technically, a scale measures a weight expressed in Newtons
but when you read a scale
it gives you mass in kilograms.
Actually the scale already knows that we're on Earth
and the influence of its gravity.
So although it measures a weight,
it converts that weight number to a mass number.
Even though weight and mass are two very different things in physics,
don't be confused by the rest of the video
because I'm going to talk about weight measured by the scale
while it gives us kilograms -
but it is weight we'll be talking about.
So Franck gets on the Wii Fit for the experiment.
When he changes position
we'll be able to observe the evolution of the force
his hands have to take.
For instance, this is what a regular push-up looks like.
You can see the weight that Franck supports with his hands
expressed as a percentage of his total weight over time.
In the beginning, Franck is up and supports 70% of his weight.
When he goes down, he relaxes his muscles and begins to drop
until he flexes again to control his position.
Once down, he hangs on for a while
then pushes away from the floor,
creating an acceleration that increases his force.
Once he is done accelerating
his weight decreases gradually until it reaches a stable point.
OK, 2 things to understand before we go further.
1. The weight that Franck supports with his hands
is not the same between the high and the low position,
there is a variation of about 10%.
The way I see it, what's happening here is that
Franck follows a circular arc with his feet at the center
and his shoulders are on the circle.
When he comes down, he brings his center of mass closer to his hands
and moves it away from his feet.
His hands have to bear more weight when he's down
since he is closer to his hands
and when he is up, his feet bear the most weight.
2. Franck's weight varies depending on the acceleration he creates.
The same thing happens in an elevator.
If you ever decide to weigh yourself when taking the elevator,
you'll see that as it goes up,
even though your mass doesn't change,
your weight will vary.
You weigh more when the elevator accelerates to go upwards
and less when it slows down before stopping.
And if we could accelerate to match the gravitational acceleration
we would no longer weigh anything
and that's how we can recreate weightlessness.
The fact that acceleration has a big influence on our measurement of weight
is especially clear when comparing push-ups
done quickly with push-ups done slowly.
The slow ones result in a variation of 64 to 90% of the weight
whereas the fast ones get it to vary between 21 and 130%.
And yet Franck's mass never changed in the meantime.
What has changed is his weight
because of the acceleration he creates by going as fast as possible.
So now we've seen what a push-up is like
and the importance of acceleration on weight.
Now we're going to compare the evolution of weight
for push-ups done on the knees, on the feet,
from a height of 30 cm,
then 45.5 cm,
then 60 cm,
then a crazy 105 cm,
and finally from a handstand with a little help to keep his legs straight.
This graph shows the weight percentage that Franck supports with his hands
as a function of his feet's height.
The measurements are made when he is up.
There is a 10% weight difference between knee push-ups and feet push-ups.
In his case, 10% is 7.5 kg.
Between the floor and the tall chair,
so between 0 and 105 cm, the difference is also 10%.
10% isn't nothing but to be honest...
I expected larger differences.
This is one of the times that physics has its limits
when applied to the body.
The transition from knees to feet is very hard
not simply because we add 10% of our weight to our hands.
It also has to do with the change in position;
on top of working the arms you're working additional muscles
like the stabilizing muscles around the spine,
the hips,
and the abs.
Those are barely engaged when you're doing knee push-ups.
Another explanation for this is the arm-body angle change.
The muscle work changes with it.
Other muscles do the work in a different way.
Those muscles may not be as well-trained
as those you use for the other position.
Hence the harder exercise.
Something else makes it hard: what you tell yourself.
First of all the sensations in your body are very different,
and when you're not used to it it may feel impossible to do.
But... maybe you can.
As for the fast and slow push-ups,
if you've ever tried both you'll know that
it's much harder to do slow push-ups than fast ones.
But according to our measurements, the fast push-ups should be harder.
On the way down, the muscles you use to go back up
are used to slow down the movement
and push against gravity.
Since they're being used non-stop on the way down,
they get tired quite quickly.
As for fast-paced push-ups, you just let yourself fall
and the muscles don't work as much - and don't get tired either.
Coming back up is another story regardless of speed.
Gravity works against us.
On a slow way up, your muscles have to generate a medium amount of force for a long time
whereas on a fast way up your muscles have to muster a huge amount of force for a very short amount of time.
When it comes to coming back up, the 2 versions are tied in terms of difficulty.
There...
I just made a video to justify why I suck at push-ups.
This video is the first of a series about sports
and how to use the data we get
in order to better understand our own performance and even how to improve.
Franck and I are going to share with you several more videos based around sports.
They'll be coming out over the next few months.
These videos are very time-consuming because of the amount of data analysis they require.
So they may not come all at once but they will be in the midst of other videos about other topics.
You'll see.
Before you go, important stuff:
if you've learned something, subscribe to Scilabus.
Share the video to tell your friends that full-on push-ups aren't that easy to do (ergo you don't suck)
or perhaps to show off how strong you are.
Do click the thumbs up button if this didn't feel like a waste of your time
and leave a comment to tell me about what push-ups feel like for you
because measurements are great but they can't explain it all.
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