No sooner than I posted about the undergraduate project that looked at Achilles loads between shod and barefoot running that this next study from the University of Wisconsin-La Crosse on the effects of loads in the Achilles tendon with different foot strike patterns turns up. Here is the abstract:
The Effect of Foot Strike Pattern on Achilles Tendon Load During Running.
Almonroeder T, Willson JD, Kernozek TW.
Ann Biomed Eng. 2013 May 3.
In this study we compared Achilles tendon loading parameters during barefoot running among females with different foot strike patterns using open-source computer muscle modeling software to provide dynamic simulations of running. Muscle forces of the gastrocnemius and soleus were estimated from experimental data collected in a motion capture laboratory during barefoot running for 11 runners utilizing a rearfoot strike (RFS) and 8 runners utilizing a non-RFS (NRFS) pattern. Our results show that peak Achilles tendon force occurred earlier in stance phase (p = 0.007), which contributed to a 15% increase in average Achilles tendon loading rate among participants adopting a NRFS pattern (p = 0.06). Stance time, step length, and the estimated number of steps per mile were similar between groups. However, runners with a NRFS pattern experienced 11% greater Achilles tendon impulse each step (p = 0.05) and nearly significantly greater Achilles tendon impulse per mile run (p = 0.06). This difference equates to an additional 47.7 body weights for each mile run with a NRFS pattern. Runners considering a NRFS pattern may want to account for these novel stressors and adapt training programs accordingly.
This was a good study and no issues with it jump out at me. Effectively they showed that a non-rearfoot strike pattern results in increased loads and loading rates in the Achilles tendon. The results are what you would expect, intuitive and biological plausible, so make sense. This will increase the risk for Achilles tendon disorders and calf muscle problems in those who use a non-rearfoot strike pattern (see: Which injuries are probably more common in which foot strike pattern?). As the authors noted, runners need to “adapt training programs accordingly” in order to ensure that the tissues are properly adapted to the higher loads.
As always, I go where the evidence takes me until convinced otherwise
Almonroeder T, Willson JD, & Kernozek TW (2013). The Effect of Foot Strike Pattern on Achilles Tendon Load During Running. Annals of biomedical engineering PMID: 23640524