Over the course of the month of July we will be focusing on all things walking related. We will explore certain critical features that are required for “normal” human gait (walking).
I have biomechanics as idols the way some people idolize celebrities, or other teachers! Over the course of this month, we will be looking at two wonderful biomechanists who have helped firmly establish the science of gait mechanics.
During this first week, I would love to let you all know a little about the incredible medical pioneer that helped document and create our modern knowledge about the biomechanics of walking.
During her long, successful medical career, Dr. Jacquelin Perry pursued many different perspectives. She graduated with an undergraduate degree in physical education in 1940, and went on to achieve her certificate (it was a certificate program at the time!) in physical therapy.
She went further in her studies, enrolling in medical school where she became deeply involved in gait studies at the biomechanics lab at UCSF. She became the first woman to graduate UCSF medical school with a specialty in orthopedic surgery.
She pursued the field of gait mechanics and over her long career as a researcher and clinician, helped to establish much of what we currently know in gait mechanics.
The gait lab is a super exciting space. There are infrared cameras to capture (so that we can later digitize) motion. There are force plates- plates flush on the floor which measure movement across them. From force plates we get direct info about the ground reaction forces (the force equal and opposite to our weight) acting on our bodies during a given movement, and also information about weight shifting. We also generally have lots of observers- PhD level researchers, assistants, therapists- to help the subject (the person being tested) get through the desired protocol.
Because having a common language to speak about movement is so crucial for our shared ideas and knowledge, I wanted to spend this first week exploring each of the critical phases of normal human gait as defined by Dr. Perry (and practiced by all medical practitioners who study gait).
For those of you who watch gait, this will be helpful for making your observations more organized. For those of you working to better understand your own gait cycle, understanding the critical phases of gait will help give more meaning to the physical requirements you need for each event.
Each of the gait events is denoted by two or three letters for abbreviation. Each gait event can be further grouped together into functional phases of gait.
Consider a gait cycle on your right limb. It would start when your right heel contacts the floor, and end when your right leg swings through- just before it contacts the floor again.
We begin and end a normal gait cycle the same each time, to maintain consistency with regard to what we are observing. Let’s go through the phases below using the example of our right leg as the limb we are studying.
Initial Contact (IC): The moment when the right foot contacts the ground.
Loading Response (LR): Weight is rapidly transferred onto the right limb. This marks the first period of double limb support
Mid Stance (MSt): The body progresses over the right, stable limb
Terminal Stance (TSt): Progression over the right limb continues (the stance limb is the leg that is supporting you on the ground, while the other leg moves through space). The body moves ahead of the limb and weight is transferred onto the right forefoot.
Pre-Swing (PSw): A rapid unloading of the limb occurs as weight is transferred to the contralateral (opposite) limb, marking the second period of double limb support
Initial Swing (ISw): The right thigh begins to advance (the knee is flexing) as the right foot comes up off the floor.
Mid Swing (MSw): The right thigh continues to advance as the right knee begins to straighten; the foot clears the ground.
Terminal Swing (TSw): The knee extends; the right leg once again prepares to contact the ground during initial contact.
Each of these phases has certain requirements to make them go smoothly. For instance, during the terminal stance phase of gait, ankle flexibility in the sagittal plane is required to allow for normal and fluid movement. During the same phase, the greatest amount of force needs to be produced by the calf muscle to allow for normal ankle/ foot motion and normal step length (hello calf raises!).
You can get a sense by looking at these phases, the breadth and longevity of Dr. Perry’s work that analyzing gait and walking can be a very complex endeavor. We are going to just go through the science with broad strokes to pull out the most common issues that I have seen in the clinic, so that you can work to avoid these pitfalls.
Next week, I will share some of the most challenging prerequisites for normal gait, and match these up with where you might find an issue in your gait cycle.
Until next time, happy moving!
Trina
