I previously wrote briefly about the importance of maintaining a good walking gait for healthy aging here and here. I promised to follow up on that in more detail, which I’m getting around to now. This took me a while because I had to do a lot of reading on the fascinating topic of biomechanics of gait [1] and how gait can degrade with aging [2, 3]. In this post I’ll go over the importance of healthy gait and the biomechanics of gait. In part II I’ll go over how gait can deteriorate due to one or more of aging, illness, or injury, and go over some exercises for maintaining gait. I will not go cover exercises for rehabilitating your gait if it is already impaired, I’ll leave that to professional therapists. But if you do already have an impaired gait I hope these couple of posts will inspire you to work on fixing it.

Degradation of gait is highly prevalent with aging, occurring in 35% of people over 70 [2]. We’ve all seen older folks with slow, shuffling gaits and short strides, which reduces the quality of life. Together with reduced balance with aging, this leads to major fall risks, leading to injuries like broken hips from which many never recover [3]. In addition, gait can degrade due to injuries and illnesses including arthritis, neurological disorders and strokes. Even when the original problem is corrected, such as through joint replacements, many people never recover a proper gait if they don’t do physical therapy exercises diligently enough.

Keeping up a vigorous walking program helps stave off gait degradation, but even that may not be enough because of age-related loss of strength. My Uncle Din was my fitness role model when I was growing up. My Mom and most of my Aunts and Uncles were pretty sedentary, but Uncle Din went for a brisk walk of at least an hour every day, rain or shine. This kept him vigorously healthy till pretty close to his passing at the age of 92. But by his 80s he was getting frail, and by his late 80s he was getting slower and his steps shorter. So even though he aged much better than people who are not active, he could have benefitted from throwing in some strength training and physical therapy.

The human upright walking gait is a miracle of evolution discussed in detail in Professor Danial Lieberman’s book Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding. Essentially, there are two parts to walking, the stance phase and the swing phase, that together make up two pendulums, one of which is inverted. The stance leg is the one whose foot is on the ground, while the swing leg is the other one. The stance leg is the inverted pendulum, pivoting about a point near the foot on the ground, while the swing leg is the conventional pendulum, pivoting about the hip. This is shown schematically in a figure from [4]:

The energy stored and released refers to the fact that our center of gravity raises in the first part of the stance phase, which takes work, but lowers back down in the second part, when we get the energy back. If you can notice this while walking it makes it feel more effortless. More on that below. Engineers are taught in dynamics class that inverted pendulums are unstable, and that is true in this case also. Picture what it is like to balance a broom handle upright with one end of it one your finger. The figure above is a side view, but the “pendulum”, your stance leg, can fall forward and back and side to side as well. Your body has to control that with muscle action, for example your hip muscles are controlling forward and back rotation about the hip (flexion/extension), side to side rotation (abduction/adduction), and rotation about the axis of the thigh bone (internal and external rotation).

This is already appearing tricky, but it’s oversimplified. For one it is only describing forward and backward motion, in a side view (the “sagittal plane”). More on that below. Also, your leg is not a broom stick, it flexes at the knee and ankle joints too. Here is a more detailed side view from [1]:

You can see some more details in this picture: the knee flexes at the beginning of the stance phase, and extends towards the end. The ankle “plantar-flexes” (points the top of your foot away from your leg) at the end of the stance phase, sometimes called “toe off”, which allows your calf muscles to contribute to propulsion.

I mentioned that a side view is not enough. There is also sideways motion, mostly at the hips but at the knees and ankle also (in the “frontal” plane). The ankles mostly plantar- and dorsi-flex (points the top of foot towards leg), but have to do a bit of sideways rotation also to adjust to uneven terrain. There are a lot of other fascinating details, described in [2].

To summarize, the muscles of the hips, knees, and ankles are used for propulsion, and other muscles, especially in the hip, are controlling rotation about three different axes. All of this has to be governed by your nervous system using balance cues. And toddlers make it look easy!

But as we are, this beautifully choreographed system can start to degrade. I’ll go over that, and what to do about it, in part II.

The final point about normal gait is that it can be enjoyable to notice some of the aspects I’ve described, like the contribution of the ankle during “toe off”, and the effortless feeling, which can almost feel like floating, during the latter part of the stance phases as the center of gravity is lowering. I used to get a very relaxing “effortless power” feeling from running, which I missed in the first few years after I had to give it up. But now I can get a similar feeling from walking.

References

1. Nordin, M, and Frankel, V, Basic Biomechanics of the Musculoskeletal System, Walters Kluwer, 2012.
2. Osoba, M, et al, Balance and gait in the elderly: A contemporary review, Laryngoscope Investig Otolaryngol. 2019.
3. Kerrigan, D, et al, Biomechanical gait alterations independent of speed in the healthy elderly: evidence for specific limiting impairments, Arch Phys Med Rehabil. 1998.
4. Lieberman, D, Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding, Pantheon, 2021