Anthropologists Believe Humans Have been HIIT training for 2 million years!
Around two million years ago, humankind was evolving and adapting to bipedalism (walking on two feet instead of four). With their hands-free from the task of mobility, humans were able to interact with their environment in completely new ways. This new ability is believed to have contributed to the rapid development of the brain. The new evolutionary leap, however, did not come without its disadvantages. Now only able to walk and run on two feet, humans would have been much slower than their quadruped ancestors. This would have been particularly important when it came to hunting.
Prior to the invention of more sophisticated weapons, humans would have relied on persistence hunting (also called endurance hunting) to catch their prey. What humans lacked in speed, they made up for in endurance and an incredible thermoregulatory system. In fact, this type of hunting was still being used in the mid-1980s by the people of the Kalahari desert in Batswana. These hunters would sometimes chase their prey for up to 5 hours and cover a distance of up to 22 miles in 104-degree heat.
Because humans can regulate their body temperature better then most other mammals they would chaise their prey during the hottest part of the day. Of course, no human can outrun an antelope so the hunt would consist of short bursts of running/sprinting followed by periods of slower tracking. Eventually, the animal would fatigue and fall. Endurance in this way became a very important evolutionary trait for survival.
If you are familiar with HIIT training you are probably able to see a correlation to HIIT at this point. For those who are unfamiliar with this style of exercise, HIIT stands for high-intensity interval training. Exercises are performed at high-intensity (80-90% of maximum heart rate) for a set period of time and then followed by a short rest. The times can vary but are generally between 30-60 seconds of work followed by a 10-30 second rest. This cycle of work-to-rest is repeated for 20-30 minutes.
This style of exercise directly correlates to earlier human evolution and persistence hunting. From this perspective, humans have been HIIT training for over 2 million years! This may be why we are so good at it and why it is so effective. HIIT training has been shown to: improve the body's capacity to burn fat, increase anaerobic threshold, improve maximal oxygen uptake (VO2 max), improve athletic performance, release beta-endorphins and much more.