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…