Arch Height Mediation of Obesity-Related Walking in Adults: Contributors to Physical Activity Limitations

Abstract: Walking and foot arch structure have risk-increasing effects that contribute to decreased physical activity in adults with overweight and obese body mass index (BMI) scores. However, it is unknown whether both excessive weight and arch height influence walking compared to the effects of excessive weight or arch height alone. The purpose of this study was to investigate if arch height mediates obesity-related walking characteristics among adults with different BMI classifications. Spatiotemporal walking kinematics and dynamic plantar pressure were collected as adults with normal, overweight, and obese BMI scores walked at their preferred speed. Digital footprints created with plantar pressure data were used to calculate a measure of arch height, the Chippaux-Smirak Index (CSI). The results showed that obese adults had lower arches than normal weight adults. Arch height was related to velocity, double limb support time, stance time, step length, and foot rotation (all Ps < 0.05). Overweight participants with lower arches had lower velocities and higher double limb support times (all Ps < 0.05). The results have implications for aiding an increase in physical activity for overweight adults via intervening in adults’ arch height.

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Alex’s Notes: Current mainstream recommendations for weight loss include a focus on increased energy expenditure through physical activity. And while I believe that exercise is better done with the intent of health improvement beyond weight loss, we cannot overlook how powerful a tool being active throughout the day is for overall wellbeing and energy expenditure. To this end, walking is a free and effective intervention.

Walking is a rhythmical activity that comes naturally to us early on in life. However, body weight is a surprising constraint, and obese adults display a number of modified gait parameters in comparison to their normal weight peers, and these differences are apparent at all three joints of the lower body: the ankle, knee, and hip. Most, if not all, of the differences in walking are an attempt to increase stability because of reduced balance, to minimize the amount of work, to decrease the load on the knee, and to reduce energy expenditure and subjective effort. Something that has not yet been examined is how all these differences in walking interact with the arch of the foot.

The study at hand recruited 89 middle-aged adults across a range of BMI categories and estimated their arch height using digital footprints and navicular height measurements (the bone on the inside of the foot above the arch). The digital footprint mat was set alongside a pressure-sensitive gait carpet to measure and graph the coordinates of every footfall, which was used to calculate various gait parameters. All the subjects simply walked across this path.

The normal weight, overweight, and obese subjects had average BMIs of 21.8, 26.9, and 34.8 kg/m2, respectively. With no differences between normal and overweight persons, the obese group demonstrated significantly lower arch heights than both the other groups. However, the obese and normal weight groups did not demonstrate altered gait parameters mediated by arch height. For the obese adults, the authors speculate that the subjects in this study were not quite obese enough to have a noticeable difference from the overweight adults, as previous studies used subjects who were more obese as well as more advanced kinematic and kinetic methods. Moreover, the footprint measurements for the obese persons could have overestimated the number of subjects with “flat feet” due to increased fat tissue. For the normal weight persons, arch height could simply be less relevant to gait parameters because these persons are better able to cope with variations in arch height.

However, arch height did mediate a number of walking variables in overweight persons. Those with lower arch heights had slower walking velocities, lower cadences, and longer step times, stance times, and double leg support times. I find it interesting that this category was just barely classified as overweight according to BMI, suggesting that these changes are very responsive to early increases in weight. But we also have no way of knowing the body composition of these subjects and it would be interesting to see how gait was affected in “overweight” muscular individuals.

So what does this mean?

In a nutshell, it means that overweight and possibly obese persons have altered biomechanical and anatomical structures as a result of their excess weight that in turn alter walking. These alterations make this simple task more difficult and uncomfortable. The authors conclude that a good fix would be providing arch support and orthotics for this population in order to increase walking ability and physical activity. Personally, I take the stance promoted by Daniel Lieberman in his book, The Story of the Human Body,

“Your foot has about a dozen ligaments and four layers of muscles that hold the arch’s bones together. Just as a neck brace relieves your neck muscles from supporting your head, an arch support in your shoe relieves the foot’s ligaments and muscles from having to hold up the arch.”

In other words, arch support is a Band-Aid. It would be far more productive to stop looking at exercise as a means of weight loss and have the overweight persons lose weight first through diet and resistance training, so that their arch height and gait parameters are not affected. Then maybe they will enjoy movement a little more and want to do it.

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