Why Do People Fall?
The short answer: gravity wins. Gravity is a wonderful thing in the sense that it keeps us grounded. For those of us who walk, we learned how gravity affects our ability to move. I believe it might have been The National Aeronautics and Space Administration that helped my profession understand where gravity influences our body.
From a biomechanical perspective, gravity influences our balance ability at our center of mass. For most of us, that center is near our belly button area. I'm not being perfectly scientific in defining the exact area because it's easier to picture that area of our body and gravity pulling down from that particular point. The below video "sees" the center of mass of the young lady and then with software a animated version is created. Stefan Iverson created the video.
The key to maintaining balance is to keep the center of mass between the feet side to side... and also from front to back. If the center moves over the toes, the person falls forward. If the center moves past the heels, the person falls backward. If the center falls to the outside of the ankle, the person falls to the side.
The key to not falling: control the center of mass. Traditionally, physical therapists use a gait belt. A gait belt is worn around the waist and is used to reduce the risk of falling while the patient is doing activities. This sounds brilliant. The problem resides in the fact the patient never learns how to control his/her center of mass. The reason is because the physical therapist controls the center of mass so the patient does not fall.
So, how can one learn how to control the center of mass? In order to learn to control the center of mass the person has to 1) be aware of the center of mass and 2) trial and error. When a person fails to keep the center of mass between the feet, the person falls. To keep the person safe, I use a harness attached to the ceiling. Patients may experience the "fall" without actually falling and hitting the ground. Typically, as more and more challenging activities are presented, patients learn to respond favorably and are able to control their center of mass.
So, now that you understand the scientific reason that a person falls... the next question: what affects a person's ability to control center of mass? I think I'll leave that answer for another day!