For over a century, the biomechanical effects of heels in everything from running shoes to stilettos has puzzled researchers and fired controversy. When standing barefoot, the perpendicular line of the straight body column creates a ninety degree angle with the floor (Fig. 1A). On a two-inch heel, were the body a rigid column and forced to tilt forward, the angle would be reduced to seventy degrees, and to fifty-five degrees on a three-inch heel (Fig. 1B) Thus, for the body to maintain an erect position, a whole series of joint adjustments (ankle, knee, hip, spine, head) are required to regain and retain one’s erect stance and equilibrium.
The slope or slant of the heel, rear to front, is called the ‘heel wedge angle’. The higher the heel, the greater the angle. On the bare foot there is no wedge angle. The bottom of the heel is on a level one hundred and eighty degrees, with body weight shared equally between heel and ball. Inside the heeled shoe, the wedge angle shifts body weight forward so that on a low heel, body weight is shared forty percent heel, sixty percent ball; and on a high heel ninety percent ball and ten percent heel.
Under these conditions the step sequence is no longer heel-to-ball- to toes and push-off, as with the bare foot. With heels two or more inches in height, little weight is borne by the heel of the foot causing the push-off phase to arise almost wholly from the ball (Fig. 2). In this reflex adjustment, scores of body parts — bones, ligaments and joints, muscles and tendons — head to foot must instantly change position. If these adjustments are sustained over prolonged periods via habitual use of higher heels, the strains and stresses become chronic, causing or contributing to compensatory strain patterns ascending up the kinetic chain.
In the recent edition of ‘The Journal of Injury, Function and Rehabilitation‘, a research team compared the effects on knee, hip, and ankle joint motions of running barefoot versus modern running shoes. Sixty-eight healthy young adult runners who currently utilize modern running shoes for training were selected. None of the participants had a history of musculoskeletal injury and they each ran an average of 15 miles per week. The experiment was designed so participants ran on a treadmill linked to a motion analysis device. They each engaged in a short treadmill run session with running shoes, and in an identical short session barefoot.
While some manual therapy techniques such as foot and ankle mobilization and structural alignment provide temporary relief from gait-induced distress symptoms (Fig. 3), long-term, they are largely ineffectual in re-establishing natural gait. Why? Because natural gait is biomechanically impossible for any shoe-wearing person. The shoe’s elevated heel shortens the Achilles tendon and tightens calf muscles sometimes leading to conditions such as plantar fasciitis and heel pain (Fig. 4).
The heeled shoe “steals” much of the body’s antigravity propulsive power by weakening the fascial stirrup and leg muscles (Fig. 5). This not only places more stress on them to achieve needed propulsion (loss of ground reaction force), but power must be borrowed from elsewhere — knees, thigh muscles, hips, and trunk. Both tendons, ligaments and muscles are, of course, vital to step propulsion and gait stamina — which may help explain the performance dominance of marathon runners from nations where the barefoot state is common from infancy to adulthood.