Flip Flop Madness. Can a flip flop reduce loading/impact force? Maybe...
We agree that the increased ankle dorsiflexion moment is to try and keep the flip flop on. This particular flip flop, the Fit Flop, has different gait parameters (see figure 2 in the article) compared to normal flip flops and barefoot. We hypothesize this is most likely due to the semi rockered design along with the heel cup. Rockered shoes reduce the amount of hallux dorsiflexion needed for forefoot rocker and reduce plantar pressures in the forefoot (1) What surprised us most were the decreased impact forces.
"The current study identified increased ankle dorsiflexor activity in flip-flop style footwear compared to barefoot, coupled with increased dorsiflexion in swing, assumed to be a mechanism to hold the shoe on the foot. The FitFlop limited foot motion in the frontal plane and significantly reduced loading at impact, compared to flip-flop and barefoot. However, it is not clear whether the reductions in these parameters are enough to reduce any potential injury or overuse injuries associated with flip-flop footwear and further, longitudinal, research would be needed to clarify this relationship." (2)
More on the subject with a free, full text below.
1. Sobhani S, van den Heuvel E, Bredeweg S, Kluitenberg B, Postema K, Hijmans JM, Dekker R. Effect of rocker shoes on plantar pressure pattern in healthy female runners. Gait Posture. 2014 Mar;39(3):920-5. doi: 10.1016/j.gaitpost.2013.12.003. Epub 2013 Dec 9.
2. Price C, Andrejevas V, Findlow AH, Graham-Smith P, Jones R. Does flip-flop style footwear modify ankle biomechanics and foot loading patterns? Journal of Foot and Ankle Research. 2014;7:40. doi:10.1186/s13047-014-0040-y.
link to free full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4182831/