8/10/2019 Cit Barefoot Running Strikes Back
1/2
BIOMECHANICS
Barefoot running strikes backWilliam L. Jungers
Detailed analyses of foot kinematics and kinetics in barefoot
and shod runners offer a refined understanding
of bipedalism in human evolution. This research will also prompt
fresh studies of running injuries.
A commitment to walking and running ontwo legs distinguishes
humans from apes, andhas long been the defining adaptation of
thehominins the lineages that include bothhumans and our extinct
relatives. This formof locomotion (bipedalism) has been around
for millions of years, and we have been unshodfor more than 99%
of that time1. The uniquelyspecialized anatomy of the human foot2is
thusa product of barefoot bipedalism, which is stillthe norm in
parts of the world. Lieberman andcolleagues biomechanical research
on thesubject (page 531 of this issue)3, therefore hasimplications
for interpreting human evolu-tion. It also has some potentially
useful andthought-provoking implications for sportsmedicine and
running-shoe design. (Full dis-closure: I dont run any more, either
barefootor in shoes.)
Most shod runners today make initial con-
tact with the ground heel-first (rear-foot strik-ing, or RFS).
Experienced barefoot runners,like the ones observed for this
study3, land onthe ground in many ways depending on theconditions
sometimes RFS, but more oftenavoiding landing heel-first because it
hurtsowing to repetitive, high-impact forces (ortransients). A more
anterior landing on a flatfoot (mid-foot striking, or MFS), or on
the lat-eral ball of the foot (fore-foot striking, or FFS),has
predictable, and some would say desirable,consequences for pedal
biomechanics. In FFSand some MFS, the foots centre of
pressurenecessarily starts more anterior at contact
and then moves backward briefly before mov-ing forward again for
toeing-off. (Sprinters,whether shod or not, also run on their
forefeet,but for different mechanical reasons.) Amongother
differences, FFS barefoot runners tend totake shorter strides and
to run with greater ver-tical leg and ankle compliance (the
lowering ofthe bodys centre of mass relative to the force ofthe
impact). This serves to blunt the transientforce and results in a
less jarring, smootherride. The elevated and cushioned heel of
mostmodern running shoes is designed for comfort,stability and to
attenuate the transient forces ofheel-strike in RFS running that
may be linked
to some orthopaedic injuries.Lieberman and colleagues
multifaceted
study3corroborates and extends what is knownabout the basic
mechanics of barefoot running,as they develop a collisional model
of the footand leg as an L-shaped double pendulum withthe same
dimensions as a typical shank andfoot. They then calculate how much
energysuch a pendulum exchanges with the groundwhen it collides at
different points and with astiff or compliant ankle. They also
broaden thecomparative human database by studying thephenomenon not
only in long-term, habitual
barefoot runners in a laboratory setting but alsoon the runners
home turf in Africa (Fig. 1).They find that FFS (and some MFS)
reducesthe effective mass of the foot and converts
sometranslational energy into rotational energy;the calf muscles
control heel drop, and theFFS runner can take fuller advantage of
elasticenergy storage in both the Achilles tendon andthe
longitudinal arch of the foot. FFS and MFSrunners therefore require
more calf- and foot-muscle strength, but avoid uncomfortable
andpotentially injurious impact transients evenwhen barefoot on
very hard surfaces.
The findings of this study complement and
strengthen Bramble and Liebermans influ-ential endurance-running
hypothesis (ERH)
for the transformation of the human bodyplan with the emergence
of the genus Homo4.The much earlier australopithecine version
ofbipedalism (as seen in Lucy,Australopithecusafarensis) was
long-lived and a great successby any standard. However, this
skeletal designreceived a major make-over near the
Pliocene/Pleistocene boundary about 2 million yearsago. Longer
hindlimbs and shorter toes arepart of this new package, and if the
ERH is cor-rect, the evolution of these features along with
a fully arched foot is probably linked directlyto barefoot
running as an integral part of anadaptive strategy for pursuit
hunting5,6. Theaustralopithecine bare foot was well-suitedfor
heel-to-toe walking and perhaps for short,rapid bursts of
sprinting7. But Lucy was not amarathoner.
The blogosphere and popular magazinesare full of debate about
barefoot running, withtestimonials to it as a more natural and
lessinjury-prone style, and often with a nod to theERH and an
appeal to the evolutionary primacyof the unshod foot. Sometimes
barefoot advo-cacy can take on evangelical overtones8. But it
is also clear that running-shoe companies andother footwear
designers are paying attention,
Figure 1 |Different footfalls. These photos are of two Kalenjin
runners from Kenya, a barefoot12-year-old girl (left) and a boy of
the same age in running shoes. Note the differences in foot
angulation as the girl prepares for a forefoot touchdown and the
boy prepares to land heel first.(Photos courtesy of D. E.
Lieberman.)
433
Vol 463|28 January 2010
NEWS & VIEWS
20 Macmillan Publishers Limited. All rights reserved10
8/10/2019 Cit Barefoot Running Strikes Back
2/2
and they should take note of this new study3.Barefoot-like
designs for footwear are cur-rently the rage, even if they still
constitute onlya small slice of the enormous running-shoeindustry.
Many shod runners never developinjuries, but the available data
indicate that atleast some (1979%) do9. Although there is nohard
proof that running in shoes, especially hi-tech or PCECH (pronation
control, elevated
cushioned heel) versions, causes injuries, inmy view there is no
compelling evidence thatit prevents them either10,11. However,
there aredata that implicate shoes more generally as aplausible
source of some types of chronic footproblems12,13.
More studies like that of Lieberman et al.3are required to
provide data instead of opinion,and testablemodels and scientific
explanationinstead of anecdotes. It is also apparent that
acarefully designed biomedical study with anevidence-based approach
is badly needed toassess the competing claims as to what, if
any-thing, is the best cover for a runners foot. It will
be interesting to see where the next foot falls,and how it is
wrapped. William L. Jungers is in the Department
of Anatomical Sciences, Stony Brook
University Medical Center, Stony Brook,
New York 11794-8081, USA.
e-mail: [email protected]
1. Trinkaus, E.J. Arch. Sci.32,15151526 (2005).
2. Klenerman, L. & Wood, B. A.The Human Foot: A Companionto
Clinical Studies(Springer, 2006).
3. Lieberman, D. E. et al.Nature463,531535 (2010).
4. Bramble, D. M. & Lieberman, D. E.Nature432,345352
(2004).
5. Rolian, C. et al.J. Exp. Biol.212,713721 (2009).
6. Lieberman, D. E., Bramble, D. M., Raichlen, D. A. &
Shea,
J. J. in The First Humans(eds Grine, F. E., Fleagle, J. G.
&
Leakey, R. E.) 7798 (Springer, 2009).
7. Lee, S. S. M. & Piazza, S. J.J. Exp. Biol.212,37003707
(2009).
8. McDougall, C. Born to Run: A Hidden Tribe, Superathletes,
and
the Greatest Race the World Has Never Seen(Knopf, 2009).
9. van Gent, R. N. et al.Br. J. Sports Med.41,469480 (2007).
10. Richards, C. E., Magin, P. J. & Callister, R. Br. J.
Sports Med.
43,159162 (2009).
11. Kerrigan, D. C. et al.PM&R1,10581063 (2009).
12. Rao, U. B. & Joseph, B.J. Bone Joint Surg.74B,525527
(1992).
13. Zipfel, B. & Berger, L. R.The Foot17,205213 (2007).
because they lack the typical T-cell surfacereceptor and do not
respond to antigens. Theydo, however, respond to IL-2, in line with
theirexpression of the common -chain receptor,which functions as
the signalling componentof the IL-2 receptor.
Moro and colleagues4name these cellsnatural helper cells and, on
the basis of similaractivation properties5, draw analogies with
the
natural killer cell (NK cell) a type of lym-phocyte that forms
part of the innate immunedefence against viruses and tumour cells,
andthat responds to cytokine stimulation and/orcell-surface
components rather than specificantigens. However, natural helper
cells lackNK-cell-lineage markers and, unlike NKcells, bear
receptors commonly found on pro-genitor (rather than
differentiated) cells, suchas the IL-7 receptor and
stem-cell-factor recep-tor (c-Kit). In view of these
characteristics, itmight be more accurate to call these
cellsnatural TH2 cells.
The abundance of these cells is limited by
the small size and number of FALCs. Neverthe-less, their
strategic location and the particu-lar cytokines that they secrete
endow themwith considerable functional impact. Indeed,Moro et
al.4show that, in mice, these cells helpto combat infection with
the hookworm-likehelminth parasite Nippostrongylus brasiliensisby
inducing proliferation of B cells in Peyerspatches (lymph-node-like
structures in thegut wall) and mucus formation, which helpsto expel
worms from the gut (Fig. 1).
The natural helper cells produce IL-5 andIL-13 in response to
IL-25 (and IL-2), and alsoin response to IL-33, an atypical
cytokine that
activates the cell through the ST2 receptor6
(Fig. 1). IL-33 is secreted largely by non-lym-phoid cells such
as endothelial cells that lineblood vessels, epithelial cells,
fibroblasts and,
IMMUNOLOGY
The expanding TH2 universeWarren Strober
TH2 growth factors, which are involved in allergy and in defence
against
parasites, are produced by many different cell types, including
a newly
identified population found in fat-associated lymph clusters in
the abdomen.
It is almost 25 years since the publication ofMosmann and
Coffmans seminal work1thatdefined two main subtypes of helper T
lym-phocyte: TH1 cells and TH2 cells. The TH2 cellsof this
dichotomy were shown to produce acollection of growth factors
(cytokines) andcell-attractant molecules (chemokines) that
areinvolved in mediating allergic responses andhost defence against
parasitic infection. But theproperties of the original TH2 T
lymphocyte arenow known to be shared by several differentcell
types. For instance, a recently reported sub-population of T cells,
TH9 T cells
2, produce IL-9and IL-10 TH2-type cytokines that exacer-
bate allergic inflammation. In addition, cellsthat produce IL-25
(macrophages, epithelialcells and mast cells) induce others to
secretethe TH2-type cytokines IL-5 and IL-13, andchemoattractants
of eosinophils inflamma-tory cells that contribute to allergic
diseases andTH2-type host defences
3. Thus, we currentlythink of TH2 not so much in the context ofa
cell, but rather as a function or, in businessparlance, a
franchise. On page 540 of this issue,another cell contributing to
the TH2 franchiseis reported by Moro and colleagues4.
The authors detected the new cell popula-tion in previously
overlooked fat-associated
lymphoid clusters (FALCs), which are scat-tered along the blood
vessels in the peritoneal
mesentery (a vascular membrane that sur-rounds part of the
intestine in the abdomen).The researchers show that these cells do
pro-duce TH2 cytokines, but that they are not T cells
Figure 1 |Newly discovered natural helper cells. a, Moro and
colleagues4identify a population ofcells producing TH2-type
cytokines in tiny accumulations of lymphoid cells, termed
fat-associatedlymphoid clusters (FALCs), in the mesentery. b, These
cells can be stimulated by the cytokines IL-25and IL-2 and by the
atypical cytokine IL-33, which signals the cell through the ST2
receptor. Naturalhelper cells produce TH2 cytokines, including
IL-13, inducing proliferation of B lymphocytes inPeyers patches and
the production of mucus, factors that counter infection with
helminth worms. The
cytokines produced by natural helper cells also support
B1-lymphocyte maintenance and productionof antibodies by B cells in
the spleen.
a b
Artery
Colon
Mesentery
FALC
Natural helper cell
(natural TH2 cell)
B1-B cell
(in peritoneal
cavity)
Peyers patch
(mucosal
lymph node)
Villi
IL-33
IL-13
IL-2
IL-25
ST2
IL-13
r ery
Colon
tery
C
Intestine
Lumen
Mucus
434
NATURE|Vol 463|28 January 2010NEWS & VIEWS
20 Macmillan Publishers Limited. All rights reserved10
