Comparing the Biomechanical Demands of Different Running SurfacesBy Dominique StasulliMost runners are creatures of habit by nature, running the same go-to routes, at the same pace, inthe same shoes, at the same time of day. Running the trusty four-mile loop around town also means the surface never changes. he creatures of habit can tell you where every pothole, overgrown bush, dip in the road, and crac! in the sidewal! lie, right down to the tenth of a mile. "f this sounds familiar, then ta!e this opportunity to learn how brea!ing new ground can be a beneficial tool in turning any runner into a biomechanically stronger one.Before comparing terrain, it#s important to consider a few factors regarding how the body reacts with the ground. "t is common !nowledge that running has an impact on the musculos!eletal system$ any non-runner will use this fact relentlessly in protest of the sport. Body mass, form, and running surface all play a role in %ust how much impact actually results. "n the most literal sense, the body &collides# with the ground with a force that is four to five times the runner#s bodyweight with each step and roughly '() times each minute *McMahon + ,reene, '-.-/.he amount of energy needed to oscillate the legs through one stride is optimi0ed by !eeping the support phase short *when one foot is in contact with the ground/ and by pushing off &reactively# *Bosch + 1lomp, 2))3/. Reactive muscles essentially recycle energy between phases as a function of muscle elasticity and ultimately save the athlete energy costs over the long haul. 4ong ground-contact results in greater energy e5penditure and less recycling. he body is required to absorb the shoc! of the ground, which reverberates through the tendons and muscles with elastic recoil, allowing the desired upward-forward propulsion to initiate, as if on spring-containing legs.6ot only do the legs act as natural, built-in springs, but the ground surface itself can also. he degree of compliance, or &give,# that a surface has, will determine the speed of energy transfer between the foot and the ground. 7arder surfaces return the energy more quic!ly, allowing the athlete to cover ground with greater speed. More malleable surfaces result in longer ground contact time, as a result of their supple properties, which is directly correlated to slower turnover,and thus, diminished ground coverage and speed. he runner#s legs, which remember, are also springs, must ad%ust stiffness according to the compliance of the terrain$ this is necessary to yieldthe optimal footstri!e duration for speed production and li!ewise, the lowest cost of o5ygen demand. "n other words, the body needs a happy medium in fle5ibility to be most economically efficient.hin! of the hard ground as a stiff spring and the soft ground as a loose spring$ this should help with visuali0ation as we brea! down the individual surfaces8Road"t may appear that the hardest surface would provide the most stable platform for push-off, and thus, allow for the greatest speed. 7owever, road asphalt is actually so dense it dampens the ability of the legs to gain vertical force from its return *9eehery, '-(:/. "n effect, the impact of the road overpowers the elastic energy return to the legs, resulting in a neutrali0ation of positive return. ;hile the muscles are busy absorbing the shoc! of impact, the road quic!ly returns the elastic energy bac! to the leg, but, the shoc!ed muscles are ill-prepared to receive it. he body attempts to &cushion the blow# by slowing the landing phase$ this &bra!ing# motion results in longer ground contact time, and slower speeds. "nterestingly enough, concrete was found to havethe most impact and least return of any surface, due to its density *9eehery, '-(:/. Moreover, a bone and %oint analysis study of sheep wal!ing on concrete over two years found thic!ened subchondral bone plates and bone corte5, resulting in less elastic bone and poor shoc! absorption*9eehery, '-(:/. "n clinical terms, this is classic, premature osteoarthritis, or