I recently did an interview with Richard Diaz for his Natural Running Network podcast. He began by asking me about efficiency in running, and I first gave an overview of the forces involved and how they break down into vertical and horizontal components. After the interview, I thought about how difficult it is to explain this concept to someone without getting lost in all the different elements that come into play as a result of horizontal and vertical force. Then it occurred to me that there’s already an almost universally understood example of how changing the magnitude of our vertical and horizontal force components changes efficiency of movement. It’s everyone’s favorite smart phone game, Angry Birds.
Consider your typical Angry Birds scenario. There are some rather smug pigs arrayed along a field at varying distances from your slingshot. You pull the slingshot back, let it go, and your birds unleash their feathered fury. Depending on which pig you want to hit and how far away they are, you have very limited options on how to get your bird to the target. There’s only so much stretch allowed by the slingshot, which means there’s a limit to the amount of force you can use. The birds all weigh the same, and their aerodynamic properties are similar (at least until you hit the screen again and activate their special powers). So there’s only one thing you can do, which is to change the angle of your shot.
Now, let’s think about what we’re actually doing when we point the slingshot further upward or downward. We know we have a finite amount of force to use. If we point the slingshot straight up, all the force moves that way. If we point it straight ahead, all the force goes that way. This seems intuitive enough, but it’s what happens as a result that really starts to illuminate the problem of efficiency in running. Point all your force up, and the bird lands right back on the slingshot. Point all your force straight ahead, and gravity causes the bird to hit the ground before he can get to the first pig. So, as we all understand, the solution is to point the bird just enough upward to resist gravity without sacrificing so much forward propulsion that it can’t get to the target.
If this ruins the game for you, I apologize, but the fact of the matter is that Angry Birds is nothing more than a repetitive trajectory optimization problem.
If you’re still in school, tell that to your teacher the next time he or she asks you what you’re doing with your phone. Maybe it will get you extra credit. Time and time again, we aim those aggravated aviary avatars with the goal of hitting new targets at different distances and behind increasingly clever obstacles. But running is a lot easier. We’re trying to hit the same target every time. We want to go as far forward and as little upward as possible. We all know that jumping rope can tire you out as fast as running without going anywhere. That’s because the majority of our energy cost in running is in the vertical direction. But rarely do we consider just how strenuous the sport of race-walking is. If walking is so easy, why is walking very fast so hard? It’s actually a matter of physics. Beyond a certain speed, trying to walk fast is like trying to shoot an angry bird straight ahead. Physics says that it’s much easier to go fast if you’ll create a little vertical force and bound a bit between steps. But the rules of race-walking obviously prevent that. Therefore, the whole principle of the competition is to go up against the laws of nature!
This is ultimately why running techniques have evolved the way we know them today. Coaches and researchers have worked together to understand what mechanics in running form best help athletes to consistently optimize their trajectory. Your coach or book on running form is a lot like those dots telling you the flight path of your angry bird. Instead of having a guy like me pop up on your game screen and resolving the trigonometric functions and resultant impact force of your bird every time you reposition the slingshot, a very smart programmer decided to make a game that was actually fun for you. And that’s what the coach is doing– making things more fun for you without killing you with math. But at least now you have a little bit better idea what he or she is doing. And the next time they tell you to work on stride visualization, you can take a break from your run and play a few rounds of Angry Birds.
If you’re interested in getting faster, you’ll be fascinated by FASTER: Demystifying the Science of Triathlon Speed. In Faster, astronautical engineer and triathlon journalist Jim Gourley explores the science of triathlon to see what truly makes you faster—and busts the myths and doublespeak that waste your money and slow down your racing. With this knowledge on your side, you can make simple changes that add up to free speed and faster racing.
Angry Birds screenshot courtesy of Rovio.