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.