She’s got legs; she knows how to use them

I often feel like my long limbs get in my way.  There is a certain lack of coordination that comes along with extra-long legs – think Bambi learning to walk.  As a runner though, many people view my long skinny gams as an asset.  I’m not convinced.  Clearly they’ve never gone shopping for full-length running tights or “capris” as I call them.  I have a permanent ring of frostbite in that space between the end of my socks and the start of my so-called pants.

Let’s look at the reigning marathon champions.  At 5’8, Paula Radcliffe is taller than the average woman, but she’s barely model tall.  Haile Gebrselassie, at 5’5, is below average height, but not dramatically so.  I read somewhere (source unknown) that most elite marathoners tend to be of average height and below average mass.  Maybe distance runners look so tall because they are so lean.  Like an optical illusion.  Long legs may sound good, but a short lean person does have less mass to carry around for 42.2K than a tall lean person.  The shorter runner may also have a flexibility advantage that could benefit running – more efficient stride, less injury susceptibility, and so on.  I don’t know for certain that taller folks are less-flexible;  I’m just saying that you don’t see many sky-scraping gymnasts.

The ‘tall is better’ theory seems to centre around the hypothesis that longer legs means a longer stride, which in turn means fewer steps over the same distance.  Presumably, over the long run (ha ha), fewer steps are more economical.  However, longer limbs may also have a greater moment of inertia, which requires effort to overcome – which is not so economical.  Anthropologically speaking, as with shorter toes, increased lower-limb length is thought to have coincided with other morphological changes observed with the appearance of Homo species.  These changes are consistent with the view that daily movement distances were much more extensive for Homo than for earlier hominins.  When the movement territory was small the cost of less efficient shorter lower limbs would have been minimal, especially in light of other advantages (like climbing).  But as the need for endurance locomotion arose, fuel-efficient long limbs became an asset.  Perhaps a must.  Or so the theory goes.

Steudel-Numbers, Weaver, and Wall-Scheffler tested whether leg-length did impact running economy.  When controlling for body mass, they found that increased lower-limb length did result in a lower cost of running.  It’s true; there is a long-legged advantage, at least in terms of locomotor economy! Long legs are more efficient, although it isn’t clear why.  It is interesting, though, that this increased efficiency was not related to stride length. The tall (or, more precisely, the long lower limbed) do have an advantage, but not because of their increased distance between footsteps.   So don’t envy the stride, envy the ride.

Ref: Steudel-Numbers KL, Weaver TD, Wall-Scheffler, CM. The evolution of human running: Effects of changes in lower-limb length on locomotor economy. J Hum Evol. 2009. 53:191-196.

Title Reference: ZZ Top – Legs. From the album Eliminator. 1983.