Tibial strain and impacts have been getting a lot of attention lately due to all the comments about heel striking being the cause of most running injuries (its not) and this is an important reason why there should be a midfoot or forefoot strike when running. Transitioning away from a heel strike does reduce that ground reaction impact, but it is not possible to reduce the load on one group of tissues without increasing it on another group of tissues. There has been very little attention in the literature to the increased load on other tissues to offload the tibial impacts. This recent study form New York University is a step in that direction; here is the abstract:
EMG and tibial shock upon the first attempt at barefoot running
Evan D. Olina & Gregory M. Gutierrez
Human Movement Science; Available online 2 May 2013
As a potential means to decrease their risk of injury, many runners are transitioning into barefoot running. Habitually shod runners tend to heel-strike (SHS), landing on their heel first, while barefoot runners tend to mid-foot or toe-strike (BTS), landing flat-footed or on the ball of their foot before bringing down the rest of the foot including the heel. This study compared muscle activity, tibial shock, and knee flexion angle in subjects between shod and barefoot conditions. Eighteen habitually SHS recreational runners ran for 3 separate 7-minute trials, including SHS, barefoot heel-strike (BHS), and BTS conditions. EMG, tibial shock, and knee flexion angle were monitored using bipolar surface electrodes, an accelerometer, and an electrogoniometer, respectively. A one-way MANOVA for repeated measures was conducted and several significant changes were noted between SHS and BTS, including significant increases in average EMG of the medial gastrocnemius (p = .05), average and peak tibial shock (p < .01), and the minimum knee flexion angle (p < .01). Based on our data, the initial change in mechanics may have detrimental effects on the runner. While it has been argued that BTS running may ultimately be less injurious, these data indicate that habitually SHS runners who choose to transition into a BTS technique must undertake the process cautiously.
This study took 18 heel strikers; they used EMG on the medial gastroc and tibialis anterior; an accelerometer on the tibia and an electrogoniometer at the knee. The subjects then ran on a treadmill at a comfortable speed in their shoes; then barefoot heel striking; then barefoot forefoot striking.
The main findings of interest were:
- peak shock in the tibia was greater in the barefoot conditions (this was measured using the accelerometer attached to the tibia as opposed to the ground impact reported in other studies).
- The time to peak shock was shorter in the barefoot conditions (indicating that vertical load rate increased when barefoot).
- The EMG activity was significantly greater in the barefoot conditions, which indicates the muscles are working harder in the barefoot conditions. The EMG activity of tibialis anterior muscle was greater in the shod heel strike condition (which is consistent with what was discussed here: Should we transition all anterior compartment syndromes to forefoot striking?).
- Knee flexion angle at contact was greater in the barefoot forefoot strike condition. The authors suggest that this is indicative of increased muscle activity of the vastus and rectus femoris muscles.
- Maximum knee flexion angle was greater in the shod heel strike condition.
- This was an acute intervention, so the results may or may not be the same after a period of habituation. See the comments here on changes in loads after habituation.
- It was on a treadmill, so may not be totally representative of overground running.
- I am sure some will find a way to have a problem with the sample size of 18; I don’t. (However, the Chi Running community were happy with a sample size of 9 when it was shown that adopting a midfoot strike decreased load!).
- This is consistent with two previous studies have shown increase strain in the tibia during barefoot running: One from Allison Altman & Irene S. Davis presented at the 2012 ASB meeting showed that “Strain rate was highest in the forefoot strike condition in both tension and compression. We expected the strain rate to be highest in the rearfoot strike condition due to the local maxima observed around the impact peak of the vertical ground reaction force” and they commented that: “However, it is plausible that the increased strain seen in the forefoot strike may be a result of muscular contraction … While peak strains were similar between conditions, strain rates were highest in the forefoot condition due to muscular contributions. It may be that barefoot running requires less muscle force than the shod forefoot condition due to the lower inclination angle of the foot at footstrike.” The other from Derrick et al at the same meeting and reported that: “Although ff running reduces the vertical impact peak relative to rf running, it requires greater plantar flexor activity. Since the gastrocnemius muscle crosses the knee joint, it requires greater cocontraction at the knee to create a similar net moment. Even though the increased muscle forces work to reduce the total moment acting at the crosssection, it is not enough to reduce the stresses because of the increased compressive force caused by the muscles. This resulted in increased stress in 3 of the 4 quadrants.” Both these studies are still in abstract form from the conference and have not been published in full in a peer reviewed journal.
- This study, to me, just confirms that the mechanics of different running forms are different and they load different tissues differently. You just trade one load for another. For one runner that may be good thing for them; for another running that may not be good for them.
As always, I go where the evidence takes me and the evidence tells me that forefoot striking, barefoot running or minimalism does not reduce the actual amount of strain on the tibia.
Olin ED, & Gutierrez GM (2013). EMG and tibial shock upon the first attempt at barefoot running. Human movement science PMID: 23643493