Ok so you’ve waited long enough. Here comes another piece to the speed and efficiency puzzle. If you missed Volume 1 on Impact, check it out!
In this installment, I wanted to point out the benefits of elastic recoil in regards to ground contact time while running. This topic is pretty straight forward, but astonishing nonetheless.
Our muscles are very elastic, much like a rubber band. When stretched, a muscle will store some of the the energy used during the stretching process. When the muscle can’t stretch any farther, the energy is released and the muscle will recoil. The easiest example is to stretch your finger back as far as it will go (without dislocating it) and let it go. Wham! See how fast your finger moved? Now try to move it that fast just contracting the muscles in your hand and forearm. Not gonna happen. The other part to the equation is that the faster you load and stretch the muscles the faster they will recoil. This can be exemplified easily by doing 2 different vertical jump tests. On jump 1, slowly lower yourself to a squat position, pause at the bottom, and then jump as high as you can. On jump 2, start from standing, quickly drop to a position between a quarter and parallel squat and explode off the ground. Which one sent you sky high, and which one seemed like a lot of work?
So breaking down the movement of a heel striker, we get heel contact with an extended leg. This essentially prevents quick stretching of the major muscle groups upon ground contact. No quick stretch, no recoil. That means it is almost 100% up to you to expend energy to make muscle contractions necessary to keep yourself moving forward. The second part to a heel strike gait is rolling from heel to toe. This movement is a huge source of wasted time and is the main source of time savings for midsole runners. More on that in a second, which includes my sales pitch to also start midsole running. The last part of the heel strike mechanic is toe off, which is actually done by contracting the calf muscles, which constitutes more muscle contractions, and more energy expended. We will talk about energy expenditure in Volume 3.
Enough about the heel strikers, let’s get to the good stuff. Those that also jump on the midsole bandwagon take full advantage of the laws of gravity and our bodies natural physiology. When the foot contacts the ground via the midsole, AND the foot is under the center of gravity, the calf muscles are immediately stretched with the help of gravity pulling you back to the earth. Once the calf is fully stretched, there is a reflexive response in the body that tells the muscles to recoil in order preserve the integrity of the muscles being stretched. This is known as the stretch shortening cycle, and creates a very powerful and efficient movement. This is not to say that you cannot heel strike under your hip. Simply landing under the hip with a slightly bent leg creates the same response in most of the major muscle groups. Thus, creating more speed laden forces. However, the calves have one of the fastest contractile velocities of any muscle in the body which means they have the ability to create a lot of extra force. Heel striking takes the calf recoil out of the picture.
Prepare for my midsole sales pitch. Here come the numbers.
There have not been a ton of studies on ground contact time, but the main argument is that midsole runners spend less time on the ground. That’s obvious. But how much time is saved? With sprinters and mainstream athletes, we aim to reduce ground contact time by .005 seconds. This basically turns into about a .2 seconds savings over a 40 yard dash. That is just an example of how the savings stack up over a short distance. One study found that elite marathoners that ran midsole vs heel strike saved about .016 seconds on the ground per stride. Now lets do some math. Most people are in the 1000-1200 strides per mile range. Staying on the low end, that would total a time savings of 49.6 seconds over a 5k, 99.2 seconds over a 10k, ~3.5 min over a half marathon, and ~7 minutes over a full marathon! Obviously you don’t have too go straight to midsole running, but bringing your foot contact under your center of mass is a must.
As a disclaimer, these numbers are not perfect and are based on a small sampling of elite runners. Many will argue that stride length is not taken into consideration when figuring these time savings. Some want to argue that the time savings on the ground can be negated by a shorter stride length. But the fact of the matter is that with shorter ground contact time comes bigger force application to the ground, and, in turn, greater stride length. In light of that, midsole runners save time on the ground, travel farther per stride, and typically make more strides per second. That is pretty straight forward.
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Until next time,
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