[0:00]If you drop down onto your hands and toes, get your back flat, your arms straight, and your hips low, then push off with both legs as your arms pull forward, you can run on all fours.
[0:13]But human arms are too short to match your legs, so you would lose speed.
[0:18]And even if your arms were longer, your spine would need to bend in a long arc, but it's designed to stay upright and isn't flexible enough.
[0:27]Your shoulder joints and wrists would eventually be injured since they can't take your full weight for that long.
[0:34]You see, humans are built for efficient upright movement and endurance, not explosive four-limb speed.
