The Effect of Training Shoes on Running Kinematics in Older Runners

Recently there has been increasing enthusiasm for minimalist shoes or barefoot running to create a more natural running style featuring a barefoot strike as opposed to the heel strike that is typically seen in the large heeled running shoes. The modern running shoe was created in the 1970s with a large cushioned heel intended to dissipate the energy transmitted to the knees and hips. Prior to that time, runners ran in a flat shoe or track flat without the big cushioned heel, stiff sole and arch support that are components of the modern running shoe. Running barefoot allows the tendons, ligaments and muscles of the foot to naturally dissipate the forces of the foot strike that are transmitted to the knees and hips⁽¹⁾.

Recently, a study looking at elite competitive adolescent runners demonstrated that they changed their foot strike almost immediately based on the type of footwear(9). The results of the study demonstrated that the adolescents landed with a heel strike 70% of the time when running in standard running shoes. However, when running barefoot they landed with a heel strike less than 30% of the time. It is not known whether the foot strike changes so abruptly in adult experienced runners with similar changes in footwear.

The effects of shoes on gait have been studied extensively with virtually all studies focusing on alterations of the shoe to accommodate existing gait patterns. Few studies have looked at whether different shoe types alter running patterns for the individual runner(2,3,4,5,6,7,8). Studies looking at groups of runners indicate that footwear does affect running mechanics, with barefoot runners having been shown to transmit less force across the knee and ankle when compared to shod runners. A heel strike pattern increases the force transmitted across the hip and knee joints by as much as three times(1).

After approval from the human subjects committee at our institution, 26 mature adult runners over the age of 30 (average age 45.5, range 30-68) were recruited to participate in the study. All participants had at least 10 years of running experience. Ten women and 16 men participated in the study. They ran on a treadmill at three different speeds with two different running conditions: shod (with their regular running shoes) and barefoot. Running speeds of 6, 7 and 8 mph were used for women and 7, 8 and 9 mph were used for men. Each speed was maintained for 30 seconds. A motion capture system (Dartfish of Alpharett, Ga.) was utilized to analyze the foot strike by a single blinded examiner skilled in the use of the camera system and running mechanics. The foot strike type was determined by comparing the angle of the ankle at foot strike to the angle of the ankle in a stationary stance (Fig 1). The percentage of heel strikes was defined as the number of heel strikes made during 10-stride data collection period at the midpoint of each 30 second running session.

Additionally, their running shoe heel–to-toe drop was measured using a custom measurement arm and a digital caliper (heel to toe drop = heel thickness – forefoot thickness). Measurements were taken at a fixed touchpoint force to account for variance in sole stiffness and curvature.

Statistical analysis was performed using Microsoft Excel (Microsoft, Albuquerque, NM) and IBM SPSS 22 (IBM, Armionk, NY) software. Two-tailed paired t-tests were used to analyze speed comparisons. Pearson correlations were used to evaluate gender, speed, running condition, heel-to-toe drop and age relationships.

There was a significant drop in percent of heel strike across all speeds for the barefoot condition (p < 0.001). There were no significant differences in foot strike noted between the various running speeds within the same condition. There was a significant difference between adjustments in foot-strike type and gender (p < 0.01). Men were more likely to persist in their strike pattern (40%) compared to women (20%) regardless of the shoe condition (fig 2). The majority of the runners maintained a heel strike. However, three women (30%) ran with a persistent forefoot strike regardless of shoe condition. No males ran with any persistence in forefoot strikes in either shod or barefoot conditions. There was a significant difference in strike pattern between shod and barefoot conditions for women at 7 mph and 8 mph speeds (p < 0.05). There was a significant difference in strike pattern between shod and barefoot conditions for men across all speeds (p < 0.05). There was a significant correlation between shoe heel-to-toe drop and age in men but not in women. There were no significant correlations found between heel-to-toe drop and foot-strike type or barefoot and shod conditions.

Barefoot running is perceived to be associated with avoidance of heel strike. It is easy to understand that a barefoot runner could not tolerate a consistent heel strike due to the lack of adequate cushion beneath the calcaneus to sustain such repetitive trauma⁽¹³⁾. Lieberman et al. have shown that runners sustain an impact force of 0.58 +/-.21 body weights in forefoot strikers versus 1.89 +/-0.72 body weights in heel strikers⁽¹⁾. Therefore, a heel-strike running form may contribute to the high number of overuse injuries sustained by runners on an annual basis. A systematic review of the literature found that 37-56% of all runners sustain a yearly running overuse injury⁽¹⁴⁾. A recent publication retrospectively evaluated the incidence of injuries of a collegiate cross country team over five seasons and found that heel strikers had nearly twice as many repetitive stress injuries as athletes with a forefoot strike⁽¹⁵⁾.

A forefoot strike may have potential advantages but recent reports also indicate a high injury rate in athletes that adopt a barefoot or very minimalist running shoe condition⁽¹⁰⁾. Alteration in the foot strike does not always occur immediately when older experienced athletes change from their standard training shoe to the barefoot condition, in contrast to the adolescent runner. Some of these runners persist with a heel strike even when barefoot at higher speeds when one would expect a forefoot strike to be more natural. These mature runners may have a much more established gait and a longer period of time may be needed to transition to a forefoot strike in the barefoot running condition or in a minimalist shoe. This may lead to frequent injuries in individuals who attempt to either run barefoot or in minimalist shoes but persist with the heel strike pattern. Therefore, older runners should be cautious when beginning a barefoot or minimalist shoe running regimen, and might consider an assessment of their gait and foot strike pattern prior to making the transition.

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Scott Mullen, MD; Megan Bechtold D.P.T.; Damon Mar, MS; Terence Mciff, Ph. D.; Heath Melugin B.S.; Bruce Toby M.D. Orthopedics and Sports Medicine, University of Kansas Medical Center