Variation in Foot Strike Patterns among Habitually Barefoot and Shod Runners in Kenya
July
Variation in Foot Strike Patterns among Habitually Barefoot and Shod Runners in Kenya
Daniel E. Lieberman 0 1 2 3
Eric R. Castillo 0 1 2 3
Erik Otarola-Castillo 0 1 2 3
Meshack K. Sang 0 1 2 3
Timothy K. Sigei 0 1 2 3
Robert Ojiambo 0 1 2 3
Paul Okutoyi 0 1 2 3
Yannis Pitsiladis 0 1 2 3
0 Funding: This work was supported by the American School of Prehistoric Research, Harvard University
1 Data Availability Statement: All relevant data are within the paper and its Supporting Information files. The raw data used to make all the analyses with the participants IDs removed has been uploaded on figshare.com at:
2 Editor: Ramesh Balasubramaniam, University of California , Merced, UNITED STATES
3 1 Department of Human Evolutionary Biology, Harvard University , Cambridge, Massachusetts , United States of America, 2 Medical Physiology Department, School of Medicine, Moi University , Eldoret , Kenya , 3 Department of Statistics and Computer Science Moi University , Eldoret , Kenya , 4 Department of Orthopaedics and Rehabilitation, School of Medicine, Moi University , Eldoret , Kenya , 5 Centre for Sport and Exercise Science and Medicine, University of Brighton , Brighton , United Kingdom
Runners are often categorized as forefoot, midfoot or rearfoot strikers, but how much and why do individuals vary in foot strike patterns when running on level terrain? This study used general linear mixed-effects models to explore both intra- and inter-individual variations in foot strike pattern among 48 Kalenjin-speaking participants from Kenya who varied in age, sex, body mass, height, running history, and habitual use of footwear. High speed video was used to measure lower extremity kinematics at ground contact in the sagittal plane while participants ran down 13 meter-long tracks with three variables independently controlled: speed, track stiffness, and step frequency. 72% of the habitually barefoot and 32% of the habitually shod participants used multiple strike types, with significantly higher levels of foot strike variation among individuals who ran less frequently and who used lower step frequencies. There was no effect of sex, age, height or weight on foot strike angle, but individuals were more likely to midfoot or forefoot strike when they ran on a stiff surface, had a high preferred stride frequency, were habitually barefoot, and had more experience running. It is hypothesized that strike type variation during running, including a more frequent use of forefoot and midfoot strikes, used to be greater before the introduction of cushioned shoes and paved surfaces.
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Runners are commonly categorized according to strike type (also known as footfall pattern),
and it is widely observed that more than 85% of habitually shod runners typically rearfoot
strike (RFS), in which the heel is the first part of the foot to contact the ground [1,2]. In
contrast, some runners (many of them elite athletes) have been observed to forefoot strike (FFS),
in which the ball of the foot lands before the heel, or to midfoot strike (MFS), in which the heel
Competing Interests: The authors have declared
that no competing interests exist.
and ball of the foot land almost simultaneously [3]. In addition, numerous studies have found
that barefoot and minimally shod runners are more likely than habitually shod runners to MFS
or FFS [4–13]. However, some habitually barefoot individuals have been observed to primarily
RFS when they run [14], and people in minimal shoes are more likely to run with a RFS than
those who are barefoot [15].
Differences in strike patterns have led to numerous hypotheses about their relative costs
and benefits. Although FFS and RFS landings do not differ in terms of economy [16–19], FFS
and some MFS landings differ from RFS landings in generating no discernible impact peak in
the vertical ground reaction force just after contact. Whether the rate of loading and magnitude
of impact peaks contribute to repetitive stress injuries is debated [20–23], but impact peaks can
be uncomfortable, often causing barefoot runners to avoid RFS landings on hard surfaces
without a cushioned shoe [7–10, 20–23].
Regardless of the advantages and disadvantages of FFS, MFS and RFS landings, one issue
that has been insufficiently considered is variation, both within and between individuals. How
much do runners vary their strike patterns, and what causes this variation? Although runners
tend to be characterized as either rearfoot, midfoot or forefoot strikers, it is likely that most use
all three kinds of strikes but in different proportions and contexts. All people FFS when
running up a steep incline, and the tendency to RFS is often greater when descending [24,25]. In
addition, runners are more likely to MFS or FFS as they increase speed [26]. Additional factors
that may affect strike type include training and skill, fatigue, the presence of shoes, shoe design,
and substrate characteristics such as stiffness, slipperiness, unevenness and ro (...truncated)