Scientists: Explain Why It's So Much Harder to Run at a Faster Pace

Running faster actually isn't that much harder if you work on your leg speed velocity (not to be confused with foot speed rapidity).

This ^ should have ended the thread.

Brilliant post!

ABSOLUTELY CORRECT!

Ah, so that’s how percentages work! But what does that have to do with dancing?

There's a legitimate question in here somewhere. Traveling at a faster constant velocity on a level track should not take any more energy from a purely physical standpoint. If our legs were wheels (i.e. your bicycle analogy) the energetic difference between 5 min pace and 6 min pace is only the difference in wind resistance (which is slight at running speeds.)

The energetic costs of running from a purely mechanical standpoint have to do with the specific costs around propulsion with legs. One way to think about "the most efficient form" would be to have a leg motion that is most similar to a wheel. It's because running is a series of leaps that require force that the energy costs increase as velocity increases according to the power equation someone talked about earlier in the thread: P = F * v.

I'll just add one more interesting thing from a physical standpoint is that the total energy required to run a certain distance is (mostly) independent of the speed that you run that distance. It takes the same amount of energy for a runner to run 8 miles at 8:00 pace as it does to run 8 miles at 6:00 pace. The only difference is the rate at which energy is expended (the power.)

If you break it down really simply, moving yourself forward at a constant speed required constant input of energy, almost all of which goes towards starting and stopping the legs every cycle. It's obvious once you think about it: With each step, your foot needs to reach zero velocity (in contact with the ground) and accelerate to more than double your running speed to get to the front. Just standing there and swinging your leg faster is harder than swinging it slower, largely the same thing when you're running.

There's another can of worms in regard to stride length and how much of that distance is covered in the air vs/ in ground contact, but that probably goes beyond the scope of this discussion.

As you approach the limit of the max speed (and related max energy output) your body can sustain your body starts giving you feedback that things are getting unsustainably hard. Google 'central governor theory'. Your body tells you it's a lot harder even though the energy output/speed haven't increased that much. If you're well below that limit then speeding up *doesn't* doesn't feel that much harder (compare the effort for running an 11 minute mile to the effort of running a 12 minute mile) This is complicated by the fact that different people have max speeds (for many people both 5 and 6 minute pace are impossibly hard). And complicated by having multiple energy system that have different limits that come into play at different time scales (e.g. 5 min pace versus 6 min pace really doesn't feel that different to me if I'm only running 10 seconds; but they feel very different if I'm running 10 minutes).

cmon man

Drag still has an exponential relationship to speed. The power needed to push your body through a medium such as air increases with the cube of velocity. The power required to go from 6 min mile to 5 minute mile increase exponentially and not linearly.

P = 1/2 pv^3 CdA

So why do photons have zero mass?

To run faster, you have to recruit more powerful muscle fibers/motor units. The more powerful the motor unit, the more quickly it fatigues.

So a well trained distance runner who can do 3 miles @12 mph can do 30 miles @10mph

But our legs are not wheels. With a loss of force, we come to a stop and the wheel on a flat surface keeps going.

More speed requires an increase in force to not only travel forward but to combat gravity.

So, it's wind resistance. That's what I figured. Thanks.

It’s not hard for me yall just slow

Yeah, that must be why it is more difficult to run on a treadmill at a faster speed. Oh wait....

Why am I so much more tired after reading this thread than I am after running a mile at six minute pace OR five minute pace?

Not sure it's been acknowledged that the question has a really multifactorial answer, with some factors certainly contributing more than others. For example, wind resistance between 10 mph and 12mph isn't much...those with physics/engineering background would be better able to quantify based on factors like frontal surface area.

I think a physiological factor that hasn't been mentioned is the oxygen cascade, which is the stepdown in the partial pressure of oxygen from atmospheric pressure on down to the diffusion of oxygen from capillaries into muscle cells and their mitochondria. When I got my physiology degrees in '07 and '09 (I've since moved to teaching secondary math so my knowledge is admittedly dated), I remember an article indicating cardiac output was the most significant determinant of performance in the oxygen cascade. So an untrained person might have a cardiac output of 15 L per min (max HR 200 bpm * 75 mL blood/beat whereas a strong athlete might have double that, 30 L/min (max HR 200 bpm * 150 mL blood/beat stroke volume) so that strong athlete is sending twice the amount of oxygenated blood that can get to working muscles, where during glycolysis and Krebs/TCA cycle that oxygen acts as the final electron acceptor, which in simple terms is basically like the last step of a long assembly line, and when that step doesn't back up, it helps everything before it happen smoothly.

I remember learning that pulmonary diffusion capacity is only important in something like a quarter of elite athletes, meaning they are pumping so much blood so fast that the blood doesn't spend enough time in the pulmonary capillaries to fully oxygenate, and so if you were to use a pulse oximeter, it'd measure a desaturation during exercise at sea level that most of us would only experience by traveling to high altitude.

In addition to improved cardiac output (i.e. bigger stroke volume via eccentric hypertrophy of the myocardium) other adaptations from training like increased mitochondrial density, increased oxidative enzymes in the mitochondria, increased growth of capillaries, improved neuromuscular activation of motor units all facilitate extended travel at higher speeds, but as other posters have said everybody finds a speed where metabolites accumulate and there's some interaction between the brain and the muscles where the brain says it can't continue this, and the metabolite interaction with the contractile apparatus and failing ability of bicarbonate buffer in the blood to buffer increase hydrogen ions pumped out by working muscle interact to slow you down.

Apologies for long post but I thought it was a cool question and the answer isn't simple. I'm sure I didn't get all of it and I'm sure I'm forgetting things, but that's what happens when you've spent the last 12 years trying to explain why you need a common denominator to add a third and a fifth. Happy running, everyone. -Lonac