I’m taking a break from my movement series this article with
a quick look at a concept very much related to my last post on improving
functional running range of motion, that of running economy.
This post was actually inspired by a great you-tube analysis
on the different running ‘styles’ observed among the elite on the lava fields
of Kona (linked here).
For what it’s worth, I very much agree with the points made
in the clip; that, among elite triathletes we see a mix of ‘classic’ runners,
i.e. the gazelles – folks embody the traditional ‘pretty’ run style &
‘functional’ gliders – athletes with a higher cadence run style that may be more
akin to a race walker than a fast moving Kenyan.
There is some scientific support that backs up the
assertions made by the presenter that some folks, (esp. slower runners with
longer limbs) running at Ironman paces may be more economical with a less
traditional, ‘gliding’ type run style, typified by a higher cadence & lower
stride length.
Hunter and Smith (2007) did a neat study that investigated
the impact of manipulating run cadence on the oxygen cost of running at a given
pace (in this case, max 1hr run pace). Their results are summarized in the
figure below…
They found a consistent ‘sweet spot’ cadence that elicited the lowest energy cost for a given pace among the runners of
1.47-1.48Hz representing a cadence of 87-89rpm, with a significant decrease in
economy (increase in oxygen cost for a given speed) above and below this. In
fact, a reduction of cadence to 80rpm resulted in a reduction in economy of
~6%. A difference of ~15mins over a good age groupers Ironman marathon!
These figures tie in well with other ‘real world’ studies of
elite run cadence ranges. Jack Daniels was one of the first to address this
question when he spent countless hours counting foot strikes of 1984 Olympians
in events ranging from the 800m to the marathon. He found that all but one
athlete fell within a relatively narrow range of 90-100rpm (~11%) despite
differences in speed of more than 30% between the events. Among the longer
distances (10k-Marathon), the range was even more homogenous (90-95rpm).
Mechanisms behind this cadence ‘sweet spot’ are still a
little mysterious, however, in vitro studies on slow twitch fibers have demonstrated a max economy plateau
that corresponds with this real world sweet spot of 90rpm (e.g. Barclay, 1994).
Similarly, studies on cyclists have shown that within muscle ‘delta’ economy is
also maximized at 90-100rpm (e.g. Sidossis et al., 1992)
OK, so assuming ~90rpm is where we want to be, what are the
implications on running stride length and ‘style’ for the competitive Ironman
athlete?
Competitive Ironman marathons (at the elite level) are run
at a speed of ~3.6-4.4 meters/sec. At 90rpm/180spm, this corresponds with
~1.2-1.4 meters per stride. Here are some comparative figures from other
running events (elite male) to bring that into perspective…
Race walk: 1.0-1.1m
Ironman – 1.2-1.4m
Elite Marathon 1.8-1.9m
800m – 2.3-2.4m
100m – 2.2-2.3m
Clearly, the Ironman marathon is quantitatively more similar
to a race walk than an elite marathon which brings into question running
teaching systems that emphasize mimicking ‘Kenyan-esque’ techniques. In fact,
when it comes to running (albeit at a slightly higher cadence and with some
reduced economy), race walkers manage to move at a comparative pace to Ironman
marathoners without leaving the ground!
This is a very
similar observation to that of the ‘Swim Smooth’ folks who have rightly
concluded that the most metabolically efficient (even if mechanically
inefficient & maybe a little less aesthetically pleasing) swim cadence for
average size athletes at Ironman paces will often result in a stroke that more
closely resembles Janet Evans than Ian Thorpe.
Ironman running is, however,
a little different to race walking. Some significant benefits to economy (~40ml/kg/km)
can be found in the slight cadence drop that comes from that ~0.2-0.3m ‘float’
from one stride to the next. However, in terms of what this optimal Ironman
style ‘looks’ like;, there is a significant difference in the look of a 20-30cm
hop vs the 80-90cm ‘bound’ from leg to leg of the shorter Kenyans. This
difference may be greater for a taller athlete like Peter Reid & less for a
shorter athlete like Mirinda Carfrae (who most closely resembles the Kenyan
style among the triathlon elite). However, particularly for folks of average
size, moving at less than elite Ironman paces, this 90rpm, short stride length
gait may result in a style that looks more like this…
Than this…
Train Smart,
AC
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