I spent much of yesterday in a meeting with Merrell footwear that was attended by several running biomechanics experts. One of the things we all lamented was the laser focus on foot strike that has arisen from the barefoot running debate and resulting discussions about what type of running form is best. Running form seems to have become synonymous with foot strike, and forefoot striking seems to have become synonymous with barefoot running. This frustrates me as there is much more to running form than foot strike, and I think there are quite possibly more important aspects of running form that are influenced by running barefoot than where the foot makes initial contact.
After the meeting yesterday I returned to my hotel room to find a bunch of references to an article that had just been published on the New York Times Well Blog. The article was titled “Is Barefoot-Style Running Best? New Studies Cast Doubt” and was accompanied by a giant photo of the Vibram Fivefingers shoes (which, strangely, have also become synonymous with barefoot running – they are not!). The article went on to discuss a study from UMass published online last month at the Journal of Applied Physiology.
The study was an interesting one. They took two groups of runners – 19 habitual RF and 18 habitual FF runners – and compared their running economy using their habitual foot strike and the reversed, non-habitual foot strike at three different speeds (3.0, 3.5, and 4.0 m/s). Foot strike was classified in the lab using both video and force parameters, and this is where one important point needs to be made. Because true forefoot strikers were difficult to find, their “forefoot” group actually consisted of 14 midfoot strikers and only four true forefoot strikers. Keep that in mind when interpreting the results – it was more a comparison between midfoot and heel than forefoot and heel. All subjects ran in the same New Balance racing flats.
Now, the NY Times reported the results as follows:
“In the end, this data showed that heel-striking was the more physiologically economical running form, by a considerable margin. Heel strikers used less oxygen to run at the same pace as forefoot strikers, and many of the forefoot strikers used less oxygen — meaning they were more economical — when they switched form to land first with their heels.”
Now, here’s what the what the authors of the study report in the text of the paper:
“We found no difference in rates of oxygen consumption or relative contribution of carbohydrate oxidation to total energy expenditure between habitual RF and FF runners performing their habitual footstrike pattern at a slow, medium, and fast speed.”
So, when runners used their usual foot strike pattern, there was actually no difference in running economy between the groups. No difference at any of the three speeds tested. This result is consistent with other studies that have compared economy between heel and forefoot strikers. They also found no statistically significant difference in carbohydrate oxidation between the two groups at any of the speeds tested, though there was a trend for “forefoot” strikers to burn more carbs. This is quite different from what was reported in the Times.
When they asked the runners to run with the opposite foot strike, they found the following:
“When performing the alternative footstrike pattern, FF running resulted in greater rates of oxygen consumption than RF running in the RF group at the slow and medium speeds and across groups at the fast speed.”
So, habitual heel strikers got less economical when they ran with a forefoot strike at the slow and medium speeds. No real surprise there as it was a novel pattern requiring greater use of the plantarflexor muscles. If I’m interpreting the results presented in their Figure 2 correctly, the forefoot strikers were equally economical when running with either foot strike at any of the speeds. It was only when the foot strike groups were combined that rearfoot striking was more economical at the fast speed. Carb usage was only significantly increased when the rearfoot strikers switched to a forefoot strike at the slowest speed.
One of the cool things about this study is that they provided data on individual changes. Group means don’t always provide a good picture of the magnitude of change that can occur at an individual level. What they found was that economy for rearfoot strikers was better when rearfoot striking for almost all individuals at the sow and medium speeds, and for roughly 2/3 of individuals at the fast speed. “Forefoot” strikers were split roughly 50-50 at the slow speed in terms of whether rearfoot or forefoot was more economical, but more tended to do better with a rearfoot strike at the higher speed. Similarly, about 75% of the habitual RF strikers tended to burn less carb with a rearfoot strike at all speeds (slightly less at the fastest), whereas patterns for the forefoot strikers were more evenly split.
How would I interpret all of this?
1. If you are a heel striker, switching to a forefoot strike will likely lead to reduced economy, at least until you become used to the new pattern. But, it’s not likely that you will become more economical with a forefoot strike even with practice (remember, there was no significant difference between habitual rearfoot and “forefoot” strikers when using their habitual foot strike). Economy is probably not a great reason heel strikers to mess around with their foot strike.
2. If you are a midfoot striker, as were most in this study, it probably doesn’t matter much what your foot is doing. Forefoot and heel strikes are equally economical. This doesn’t surprise me much since a midfoot strike is kind of a middle ground between forefoot an heel striking (in fact, my guess would be that they might use multiple foot strike types when they run).
3. There was a tendency for forefoot strikers to burn more carbs. The authors reference a paper I published which showed that midfoot and forefoot strikers tend to switch to a heel strike late in a marathon. Thus, if your plan is to race a marathon, there may be an advantage to a heel strike (a mild heel strike I’d guess).
4. This study was conducted on a treadmill, so we do have to be careful about extrapolating the results to a non-compliant, harder surface like a road.
Now, one part of this study that I haven’t mentioned up to this point is that the authors also measured some kinematic variables. Two of the variables they measured were stride length and stride rate. The focus of the study was to compare running economy, but my guess is that most people considering switching foot strike are doing so not to make themselves more economical, but do so because they are dealing with some kind of injury and think that a switch might help. People generally don’t take up barefoot running out of a desire to race faster, they do so because they either enjoy it or have found that running in shoes just does not work for them. When groups were combined, they found that rearfoot strikers tended to take longer and slower strides (about 2% longer, and 2% slower). Previous research has shown that an increase in stride rate of even just 5-10% can reduce loading on the knee and hip (again emphasizing here that there’s more to running form than just foot strike!). So, there my be a tradeoff whereby a forefoot strike may at times be less economical for some individuals, but they may benefit in other ways such as via a shorter, quicker stride with reduced loading of the knee/hip (but possibly increased loading of the foot and ankle).
As always, I come back to the individual. If you’re a forefoot striker, there’s probably not a big benefit to trying something else except maybe if you plan to race a marathon or if you have injury issues that can be linked to your contact style (foot, ankle, calf problems perhaps). If you are a rearfoot striker, you’re probably not going to become an elite runner by switching your foot strike. You may, however, shorten your stride up a bit which could be good for other reasons (e.g., reduced loading). Consider the tradeoffs, and figure out what’s best for you and your needs.