What a Girl Wants; What a Girl Needs

By Samantha Lipsky

On October 7, 2001, over thirty thousand distance runners came together to complete 26.2 miles at the Chicago Marathon. I was fortunate enough to be a participant that chilly day. After reflecting and panicking about my own mortality, I looked to the immense crowd of runners. Men and women of all ages were moving their limbs to get to the finish line. Observing such a large cross-section of the population made me wonder (in a nerdy, curious sense) about the variety of demands placed upon running shoes-the instruments of this odyssey.

Today, many types of running shoes are marketed to various demographics. Currently women are taking up the sport of running at an increasing rate. Women are definitely built differently from men. According to Atwater (1990), "The most obvious musculo-skeletal differences of male and female athletes are body size, and composition, as well as skeletal dimensions, particularly hip width and shoulder width." Notably, the Q angle (the relationship and alignment between the pelvis, leg and foot) is about 5% larger for females than males. The larger angle can predispose women to injuries of the lower back, pelvis, hip, knee or ankle, due to the stress associated with the repetitive motion of running. In addition to the Q angle, the average woman is shorter, lighter and has about 8% to 10% more body fat than the average male. Further, female runners tend to have a lower percentage of muscle mass and less bone weight than males. All of these factors contribute to athletic injuries among females.

The demand for biomechanical corrective shoes for women is a reality. Shoe companies "sensitive" to the athletic needs of this demographic are promoting footwear with a narrower fit for females. Most times feminine shoes look similar to male counterparts, with maybe a different color scheme. The question remains: would a tailored shoe prevent biomechanical injuries among women? Could women just as easily run in men's shoes?

The foot is a complex piece of machinery. The skeletal structure starts at the ankle. According to Medical Multimedia (2001), two bones from the lower leg (the large tibia and smaller fibula) join at the ankle to form a very stable "mortise and tenon" type joint. Using lumber terms, the tenon (or fibula) fits into a slot in the tibula to form a sturdy hinge-like connection.

Two more bones make up the hindfoot, the talus and the calcaneus. During running when the heel first strikes the ground, these two bones feel impact forces at initial contact. The impact forces are then transmitted to the upper parts of the lower extremities. According to The Biomechanics of Running Shoes, the duo is attached by a freely moveable joint system, known as the subtalar joint (Luethi, Stacoff, 1986). Thus, the foot can bend up and down due to the ankle joint and roll side to side via the subtalar joint.

There is an associated tissue that runs from the calcaneus to the ball of the foot is known as the plantar fascia. It is a dense structure that helps support the longitudinal arch of the foot. When the foot is on the ground a tremendous amount of force is concentrated on the plantar fascia. This can lead to stress on the plantar fascia where it attaches to the calcaneus.

The next group of bones, adjacent to the subtalar joint, is the tarsals. When the foot is twisted in one direction by muscles from the foot and leg, these bones lock tightly in place. However, when turned the opposite direction, the bones unlock; they can flop around to conform to whatever surface the foot is contacting. One type of motion associated with the tarsal bones is pronation (the rotation of the medial bones in the midtarsal region of the foot inward and downward so that in running the foot tends to come down on its inner margin). In addition, there is also supination, or underpronation, which according to Runner's World, is the insufficient inward roll of the foot after landing.

Firmly attached to the tarsals are five long bones-the metatarsals. These bones serve mainly to resist compressional load. When standing the foot is primarily supported at three points: the calcaneus, and distal bases of first and fifth metatarsals (Luethi, Stacoff). Lastly, there are the bones of the toes, the phalanges. The joints between the metatarsals and the phalanges form the ball of the foot. While, there is not a lot of motion between the bones of the phalanges, the hallux, or big toe is the most instrumental toe for walking.

Earlier this year at the Symposium of Footwear Biomechanics in Zurich, Switzerland, E. M. Henning explored the gender differences for running in athletic footwear. Henning's experiment tested 15 women and 17 men of the same body weight, height and age. (Interestingly, the two sexes have similar stride lengths and rates when the same body height or leg length is compared.) They all wore the same shoe sizes and tested five types of shoes: three different men's shoes and two styles of women's shoes. The subjects ran across two "Kistler" force platforms, with a velocity of 3.3 m/s. The Kistler platform measured ground force reactions, tibial acceleration, angular rear foot motion, and plantar pressures at eight chief locations on the foot.

Running velocity, ground contact time, various vertical forces, and peak tibial acceleration (the turn-around motion of the lower leg) were recorded. Also, the types of motion: supination at contact (how much the foot turned outward when it hit the ground), maximum pronation and peak pronation velocity (the rate of inward motion) were determined. Pressure was also a related factor. Plantar pressure, peak pressure rates, and relative loads were found under the following components: lateral and medial heel, lateral and medial midfoot, under the heads of the metatarsal bones and the hallux. (The plantar pressure is the stress the plantar fascia feels corresponding to the locations of the attached bones.) Relative loads (in %) were calculated by dividing the force-time integral under each of the anatomical landmark during ground contact by the summed integral of all force sensors. All subjects performed five repetitive running trials in each shoe type. The shoes were assigned randomly. Prior to further statistical evaluation, the variable means of the 5 repetitive trials in each shoe were calculated. Statistical information was compiled using a two-way table to investigate the effects of gender and footwear type.

In general, the results showed that none of the variables demonstrated a significant interaction among gender and footwear type. This means that women had the same biomechanical dilemmas in men's shoes as they did in their own footwear. Women demonstrated significant to highly significant differences for the following: the impact in their vertical ground force reaction, peak tibial acceleration, maximum pronation, peak pronation velocity as well as all peak pressures (except for peak plantar pressure under the hallux) and peak pressure rates (except for rates under the hallux, and rates under the third metatarsal). Thus, under all foot regions pressure rates for men were consistently higher. The relative load analysis showed a reverse loading behavior of women against men in the heel and midfoot areas. The men displayed significantly higher heel but less midfoot loads than the women. Thus, women's arches are not supporting the middle of their feet. This data points toward an older study that there is a stronger collapse of the longitudinal arch for the women during weight bearing, as it has been reported previously (Hennig et al., 1993). Further, a weaker foot structure for the female runners would also explain the increased tendency of pronation and the smaller amount of pressure to the ground as well as pressure rates under most anatomical landmarks (except for the midfoot). Although the women's running velocity and ground contact times were virtually identical to the men's times (due to similar stride length), the softer pressure is once again represented by a significantly lower passive impact peak. While a lot of biomechanical irritations are unresolved, new shoes are released all of the time in new models. My best advice to ladies out there is this: buy shoes that protect against overpronation. Most brands have a shoe style built for overpronators, which help prevent knee injuries. Also, have a good run!

References

Atwater, A. E. (1990). Gender differences in distance running. Biomechanics of distance running. P.R. Cavanagh. Champaign, Illinois, Human Kinetics: 321-362.

Hennig, E. (2001). Gender differences for running in athletic footwear. Retrieved December 4, 2001, from the World Wide Web: http://www.uniessen.de/%7Eqpd800/FW2001/LITPDF/Hennig21%20rtf.pdf.

Medical MultiMEDIA Group. (2001). A patient's guide to the anatomy of the foot. Retrieved December 4, 2001, from the World Wide Web: http://www.medicalmultimediagroup.com/pated/foot/anatomy/anatomy.html

The Biomechanics of Running Shoes