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This is a continuation of my last post: Another reason humans are so good at running is we have big butts. I'm not joking. Humans have larger gluteus maximus muscles than any other other species on earth and the gluteus maximus is the most powerful muscle in the human body. Daniel Lieberman, chair of the Department of Human Evolutionary Biology at Harvard University, conducted a study of gluteus maximus function and found that the glutes are much more active while running than while walking, indicating that they evolved for the purpose of running. So what does your butt do for you when you run? Primarily it provides the power needed to run, so much power in fact that double amputees without hamstrings or quadriceps like Rudy Garcia-Tolson are able to run with nothing but their glutes. The glutes also serve a secondary purpose of pushing the hips under the abdomen, eliminating lardosis (backwards bending) in the spine which reduces impact on the back and allows for more use of deep abdominal muscles such as the psoas (pronounces so-az). Another reason humans are so good at running for long distances is that unlike pretty much every other animal on earth that can run, our respiration isn't tied to our stride. In in which I described why cheetahs are so fast I explained how the breathing of some quadrupeds (animals that walk on 4 legs) is regulated by organ movemenet amplifying changes in chest cavity pressure which makes quadrupeds necessarily inhale and exhale once every stride cycle. Since humans are completely bipedal our respiratory system is entirely independent of whether we're running or not, allowing for varied breathing patterns. 1-1 and 2-2 patterns (ex. inhaling for 2 steps then exhaling for 2 steps) are great while running fast because they allow for more oxygen intake but it is hard to run far while hyperventilating. In contrast 4-4 (or 3-4/ 4-3) is a better pattern for running far but makes running fast more challenging (most runners usually wont go any slower than 4-4 because anything sustaining anything slower requires running pretty slow but I have been able to sustain an 11-11 pattern for a few minutes of slow jogging- it's not very practical but its cool to be able to do). The fact that humans can control their breathing independent of their speed allows us to maintain an ideal oxygen level for running very long distances.
In my last post I highlighted some of the incredible things that distance runners are able to do, including very long runs at altitude (lower oxygen) and in extreme conditions. But what allows these people to do these kinds of things? The short answer is training. With enough training almost anyone (for the most part excluding the very elderly) could finish an ultra marathon. But why is this? The answer lies in the fact that humans are better adapted to run for long distances than any other animal on the planet. First of all, humans are bipedal meaning that we move around on two feet, and while other primates are able to walk with two limbs humans are the only primates who walk exclusively with only two legs. Bipedalism in itself isn't incredibly unique as other mammals such as macropods (kangaroos, wallabies...) and large birds like ostriches and emus rely on bipedal movement as well, however humans have other adaptations to make bipedalism more efficient. You may not realize it but the human foot is a very intricate mechanical structure containing 26 bones, 33 joints and over 100 muscles and tendons. While running the foot, specifically the arch, acts as a spring which absorbs and returns force to the ground which is done as follows: the foot lands on the outside of the forefoot and pronates inward, stretching muscles which absorb and store force. The foot rocks forward while it pronates so that by the time the front pad of the foot is flat on the ground the toes are pushing off the ground with the energy stored in the foot's muscles. In addition to the feet the rest of the muscles act as springs which store energy from the foot strike to be used as propulsion for that step. As a result, running is basically a process of converting kinetic energy (foot strike) into potential energy (stretched muscles) and back into kinetic energy (push off). Of course as in any system, energy is lost as heat thus cells must break down glucose during anaerobic and aerobic respiration to create ATP for your muscles to use to create additional energy to put into the ground.
First things first: I would like to complain about the fact that people are not at all creative while heckling runners. You may think that shouting "Run Forrest, run!" out of your car window is funny and original, but its not. I've heard that at least 20 times in the last few years. In case you have never seen the movie Forrest Gump (shame on you if you haven't, you don't deserve to be a person) this is a reference to the scene when protagonist Forrest is being chased by bullies and his friend Jenny yells "Run Forrest, run!" so he does causing the braces to break off his legs and allowing him to take off full sprint through a field, escaping the bullies and discovering his running ability (I shouldn't have even had to explain that...) Later in the movie Forrest runs across the US several times which is quite the display of distance running ability. But this is far from fiction- since 1909 there have been 283 recorded crossing of the continental US on foot by 252 individuals. Other extreme running feats include the Ultramarathon which is a race longer than a marathon, which is 26.2 miles (42.2 km). Some extreme examples include the Leadville 100 and Western States Endurance Run, which are both 100 mile races run on mountain trails at elevations of over 10000 feet and contain 15000 to 18000 feet of climbing and descending, and the Badwater Ultramarathon which is run 135 miles through death valley (average air temperature of 120 degrees F) and finishes by climbing 13000 feet up Mount Whitney. In the during this race the road surface gets so hot that runners must run on the white lines on the side of the road to keep the soles of their shoes from melting though participants usually go through several pairs throughout the race anyway