Several interesting studies have come out over the past few weeks that have in one way or another focused on the running foot strike. The first that I’m going to cover is by Jason Bonacci and colleagues and addresses how running mechanics differ between barefoot running and running in a “minimalist” shoe (Nike Free 3.0), racing flat (Nike Lunaracer 2), and “regular” running shoes (a runner’s typical training shoe, variable by individual). The study is titled “Running in a minimalist and lightweight shoe is not the same as running barefoot: a biomechanical study” and was released in Online First form on the British Journal of Sports Medicine website.
The authors recruited 22 highly trained, high-level runners (mean 10K time of 33 minutes) and provided them each with a pair of Nike Free 3.0 and Nike Lunracer 2 running shoes. They were given 10 days to run a few times barefoot and in the new shoes so that each condition would not be entirely novel. They also ran in their usual running shoe (which was on average about 125-140g heavier than the two lightweight shoes).
The researchers filmed the runners with a 22-camera 3D Vicon system on an indoor track, and measured force using 8 force plates (this was a pretty high-caliber setup). The combination of cameras and plates allowed them to capture biomechanical data from a 20m long section of the track.
After a warmup, Each runner performed 10 running trials in each of the four conditions (barefoot, Free, Lunaracer, variable standard shoe). Average speed was 4.48m/s (about 6:00/mile) during the trials, so they were running far faster than most recreational runners.
The results of the study basically showed that running barefoot is a lot different than running in shoes, but that the three shoe conditions didn’t differ all that much.
The only real difference between the shoes was that runners tended to have shorter, quicker strides in the Frees and Lunaracers vs. their standard shoe (mean cadence 183.9 steps/min for both lightweight shoes vs. 181.3 steps/min in standard shoe). The Nike Free did reduce peak ankle adduction during stance and increased peak ankle internal rotation moment equivalent to barefoot, but in all other respects was more similar to the other shoes.
The real standout here in terms of biomechanical differences was barefoot running. Here are some of the key differences that were found for barefoot relative to the shoes:
1. shorter stride length than all shod conditions
2. higher cadence than all shod conditions (avg. 187.7 steps/min)
3. less dorsiflexion of the ankle at initial contact (i.e., flatter foot placement at contact)
4. greater ankle plantarflexion at toe-off
5. reduced knee extension and abduction moments
6. less knee flexion during midstance (straighter leg)
7. smaller joint moments and less work done at the knee (24% less negative work when barefoot compared to the standard shoe)
8. greater joint moments and more work done at the ankle
The authors summarize by saying: “Knee and ankle mechanics when running barefoot were different to all shod conditions, including the minimalist shoe, indicating that the minimalist shoe cannot entirely replicate the mechanics of running barefoot.”
This study provides further confirmation for a pattern that we are starting to see over and over. That is: barefoot running mechanics are different than shod running mechanics, particularly when comparing barefoot to a well cushioned shoe. Barefoot running tends to reduce work done by the knee and increase work done by the ankle. From a therapeutic standpoint, barefoot running may have benefits to those with knee issues, but may put the foot, ankle, Achilles, and calf at greater risk. Thus, knowing the individual runner and their needs/weaknesses is critical to avoid trading one set of injuries for another.
What I particularly liked about this study is that the authors were very open about admitting its limitations. For example, they point out the the Nike Free has quite a bit of cushion and an elevated heel. Habitual barefooters jump all over anyone who claims that the Nike Free replicates barefoot running, and this study seems to prove them right, at least in terms of how it affects biomechanics (and much to the chagrin of Nike marketing…). Studies of less cushioned shoes (e.g., Vibram Fivefingers) have revealed more similarity to barefoot running, but even ultraminimal shoes don’t seem to be a perfect mimic to running without footwear. They also admit that by not controlling the standard shoe they may have not as easily detected differences between the minimal and more traditional shoes.
Another important point that the authors emphasize is that their subjects were very highly trained runners and that as a result they might “already have highly consistent running mechanics and different types of shoes have little influence on their running gait.” They indicate that “It is possible that lesser trained runners with less consistent mechanics may be more susceptible to changes in running gait when utilising a minimalist shoe.” As always, one must consider the subjects and conditions studied when applying the results of a scientific study, and I’d once again love to take a look at individual variation.
The authors end the paper with the following conclusion, which I feel is a very nice summary of the implications of their study:
“In conclusion, the dynamics of running overground while barefoot are different to that of running in a minimalist shoe that has cushioning and an elevated heel. Athletes and their coaches should not expect to instantly replicate barefoot running while in a minimalist shoe. Running barefoot does induce mechanical changes to habitually shod highly trained runners gait and it is inherently different to shod running. The increase in work done at the ankle must be considered when transitioning to running barefoot as too rapid a transition may overload the triceps surae complex. Conversely, the reduction in joint moments and work done at the knee while running barefoot may provide potential benefits for the management of knee pain and injury.”
You can read the abstract to Bonacci et al., 2013 here: http://bjsm.bmj.com/content/early/2013/01/10/bjsports-2012-091837.full