Hey everyone! We're back to talk about the heart of athleticism – the one thing that makes athletes soar like superheroes: the impulse-momentum relationship!
This isn’t rocket science – okay, well, maybe it's a little bit of rocket science – but we'll break it down like we're explaining it to our favorite workout buddy! We'll go over how forces, time, and momentum team up to create those gravity-defying jumps, explosive sprints, and jaw-dropping lifts.
Forget about boring lectures and snooze-inducing theories. We're diving into the juicy stuff that makes athletes unstoppable! Picture this: you're watching your athlete smash records, and you think, "How do they do it?!" Well, it's all about the science of "oomph" and perfect timing!
We've got your back with real-life examples and practical tips. Whether you're a strength coach, a pro at rehabbing injuries, or the guru of agility training, we've got something exciting for you!
Throughout this journey, we'll explore the art of generating and managing forces, effectively utilizing time to optimize performance, and comprehending the importance of momentum conservation. By understanding these principles, you'll gain valuable insights into how you can maximize your athlete's training programs or refining your own athletic endeavors.
At its essence, the impulse-momentum relationship explains the integral connection between force and time, revealing how they synergistically influence movement and performance. Whether it's a sprinter accelerating on the track, a weightlifter hoisting unimaginable loads, or a gymnast executing gravity-defying maneuvers, the impulse-momentum relationship plays a pivotal role.
Laws of The Land
If we are going to discuss physics, we have to mention the OG strongman Sir Issac Newton. You know, the person who came up with this whole talk about Newtonian Physics. If it wasn’t for him, none of us would be talking about ‘throwing it up’ or ‘dropping it low’. Well, at least not without understanding how we were doing it accurately.
To keep things simple, we are going to talk about his 3 laws of motion and how they apply to our world of training:
1. Newton's First Law - The Law of Inertia
Newton's first law states that an object at rest (not moving) will stay at rest, and an object in motion will keep moving in a straight line at a constant speed unless something else (like a force) acts on it. This concept is called inertia.
In simpler terms, things like to stay as they are – if they're not moving, they don't want to start moving on their own, and if they're already moving, they don't want to stop without a reason. So, you need a push or a pull (a force) to make objects change their state of motion.
2. Newton's Second Law - The Law of Acceleration:
Newton's second law tells us that the amount of acceleration an object experiences is directly related to the force applied to it and inversely related to its mass.
This law is often summarized with the famous equation: Force = Mass × Acceleration. It tells us that the bigger the force applied to an object and the less mass it has, the faster it will accelerate.
3. Newton's Third Law - The Law of Action and Reaction:
Newton's third law states that for every action, there is an equal and opposite reaction.
Think of it like this: When you kick a soccer ball, your foot applies a force to the ball, and the ball, in return, applies an equal force back on your foot. That's why you feel your foot being pushed backward a little bit.
What is The Impulse-Momentum Relationship
In my last post, ‘An Introduction to Velocity Based Training’, one of the main points I made was that VTB was not a different way to train, but a different unit of measurement to emphasize. In short, velocity-based training is just training.
So, you might be asking, “Why is VBT a thing if it’s just the same as the other strategies? Why re-invent the wheel?”
Well, the theoretical foundation of VBT is rooted in the force-velocity curve, which describes the relationship between force production (impulse) and the resulting velocity of the mass(momentum). The same can be said for traditional percentage-based training. In its most simple form, we are just trying to exert energy to create enough force and apply it to a mass so that it moves its position. But how do we know how much force we need to produce? And (generally speaking) the purpose of training is to produce more force. So how do I know if I am producing more force if I’m moving the same mass that I was already moving before?
This is why it’s important to understand the impulse-momentum relationship because it is a foundational concept to athletics and locomotion. Our muscles produce force through contraction, and that force is transferred through movement by torque at our joints. With maximal force production, our joints will move with maximum angular velocity. But when they are faced with opposed resistance, the velocity will be the net result of those total forces.
Key calculations
First, I want to start by setting the table with these key calculations. These are the foundations to understanding the resistance in resistance training.
Obviously, giving you these terms and definitions alone is the least helpful thing I can do. So let me give some context to their meaning and how they relate to each other…
Squat Jump Example
One of the best visualizations of this is the squat jump. In the squat jump, the athlete will start in a squatted position (paused) and attempt to jump as heigh as possible, as fast as possible. A true squat jump shouldn’t have any countermovement (downward or loading movement). This is why it’s a great example of the impulse momentum relationship.
Since the athlete is still at the start of the exercise, their average force is equal to that of their body weight. Yes, they are undoubtably using metabolic energy for their muscles to create force and maintain their position at those joint angles. But regarding their center of mass (CoM), they are in a stationary position and thus have no velocity. So, as we noted earlier, the ground reaction forces are equal to their body weight.
Well, to initiate the jump and start to move upward, the athlete needs to push away from the ground. The increase in force from the legs extending moves the CoM upwards because the force applied by their legs is greater than that of gravity. Well, not only that, since they have now started to move their position upwards, they also have positive velocity and acceleration. This means they are now experiencing momentum upward. So, the successive moments will include the kinetic energy from their legs producing force, and the potential energy from their momentum.
This is where the magic happens…
If enough force is generated quickly (impulse), the athlete will have compounding incremental increases in velocity (acceleration) that will surpass the acceleration of gravity. This means that they become superhuman and have entered the matrix!
Well not really, but they have created enough acceleration so that they are overcoming gravitational pull and now have so much momentum upwards that they will continue to move upwards until the negative (downward) acceleration of gravity slows them down and they are force to return to earth with the rest of us mortals.
More Mass, More Force
Now that we see how this works, let’s bring it back to training. Well, that example was talking about an athlete’s body mass. What about adding external mass, like a barbell and weights? That’s what we do, right? This is the logic and the physics behind resistance training. The added mass of the bar, dumbbell, and weights (or resisting force from elastic bands) means that we have to generate more force to create movement. And the more force we create in the least amount of time will result in a greater velocity. The higher velocities we can achieve in shorter distances is representative of increases in power.
The last part is really important. Although we often get caught up in the weight we can resist, or the force we produce, it is not the end result for ground-based power sports. We are doing the training to improve our power output. This is why velocity can be such an impactful metric for training when considering training adaptations and effect. Lifting more weight may not be the goal for all of your athletes. For some athletes, it might be moving weight faster.
With all things accounted for, force is still the predominant variable. And it will impact all of the other outcomes. But when it comes to fine tuning your training and really getting the most transfer of training, we should really consider looking beyond mass and remember the impulse-momentum relationship. And what that tells us about what we should really value emphasizing for our athlete’s KPIs.
Well, that's was the 'not-so-painful' physics lesson for the day. Remember to check back in to catch upcoming posts about how we can better understand the science behind our training, so that we can continue to push the boundaries of human performance!
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