When two-legged animals walk, they have to alternate standing on one leg in balance, creating a metronome motion. Their maximum strolling speed depends on their metronome frequency that is inversely proportional to their body length. For humans, this is 2.9 km/h. To walk faster, people need to increase their metronome frequency. Humans and ostriches are the only two species capable of this. Humans naturally do this with their oblique muscles. But when those become weak, they switch to their biceps. However, the oblique muscles can access much more energy.
About 30 years ago, this newspaper https://www.volkskrant.nl/ wrote that our ancestors suffered a mutation about 5 million years ago that left them unable to produce vitamin C and forced them to eat plants. But plants contain much more sugar, and sugar is very bad for the capillaries in the eyes, liver, and kidneys. That’s why people with diabetes 2 are at risk of going blind.
If a second mutation hadn’t occurred within a few years of the vitamin C mutation, solving the sugar problem, our ancestors would have become extinct 5 million years ago. It’s even possible that millions of mutations occurred that weren’t viable. But at least one mutation solved the sugar problem.
The back door of the oblique muscles was opened.
All muscles are capable of converting sugar into adenosine triphosphate. ATP is the actual fuel for muscle cells. The oblique muscles are capable of depositing these ATPs into the bloodstream. Two million years ago, when the elongated feet evolved, the body needed extra energy. As a result, the calf muscles are also capable of depositing ATPs into the bloodstream.
According to my GP, the liver is capable of converting fat into sugar. Of the available sugars, the oblique muscles process about 80%. The calf muscles process about 10% of the sugar. The remaining 10% is divided between the thigh muscles, arm muscles, and gastrointestinal muscles. This means the oblique muscles can access approximately 200 times as much energy as the biceps.
When the obliques and calf muscles weaken, the body is no longer able to process large amounts of sugar. This is why people with love handles are at risk for type 2 diabetes.