More Flip Flop Madness. Can a flip flop reduce impact forces?

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/

Flip Flops not so bad? We still think they suck and here's why...

We have talked about the dangers of open back shoes (Including flip-flops)  and loss of ankle rocker as well as changes in forefoot rocker and great toe dorsiflexion on our blog many times.

The findings of this study, with slower cadence and shortened stance are not surprising (especially since you need to fire your long flexors to keep them on!) nor are ankle joint kinematics (flip flops have no heel counter and are not torsionally rigid, so naturally there would be increseased subtalar motion), however we really question the interpretation.

 "Many have long suspected the answer, but a new study would appear to resolve the question: Are flip flops really that bad for your feet? According to Chen and colleagues from the Department of Biomedical Engineering at The Hong Kong Polytechnic University, flip flops are most likely no better than barefoot when it comes to lower-limb co-contraction and joint contact force in the ankle. The authors had hypothesized that the popular rubber footwear would increase co-contraction of the muscles between the knee and ankle joints in what they thought was a compensatory mechanism for the unstable foot–sole interface and would affect gait kinematics and kinetics.

In the study, the researchers had 10 healthy males perform 6 walking trials under 3 conditions: barefoot, sports shoes, and thong-type flip flops. Participants, who reported they were not “regular flip flop wearers,” were fitted with numerous markers that were monitored while they walked on a 10-meter pathway. The study looked at several muscle pairings that stabilize the knee, ankle, and subtalar joints, including vastus lateralis and gastrocnemius medialis; vastus lateralis and biceps femoris; and peroneus longus and tibialis anterior.

In pairwise comparisons, the walking velocity of flip flops was lower than that of sports shoes (p<0.01) but comparable to barefoot (p>0.05), findings that were consistent with the published literature. Although not significant, the minimalist footwear produced a slower cadence and shortened stance phase in walking trials compared to the other 2 types of footwear. Joint kinematics differed significantly in the ankle joint (F[2,18]=6.73, P<.05) and subtalar joint (F[2,18]=4.45; P<.05); Furthermore, ankle and subtalar range of motion was higher for flip flops than for sports shoes. However, co-contraction was not enhanced. The authors propose that walking speed does not need to be consistent for real-world activities and the slower speed could be a natural approach to avoid injury.

The authors conclude that the slowed walking speed of flip flop users could account for the comparable joint biomechanics between flip flop use and barefoot. They note, however, that, for injury prevention, the closed-toe design of the sports shoe would provide better support for joint motion and loading compared to the other 2 options."

Source:

Chen TL, Wong DW, Xu Z, Tan Q, Wang Y, Luximon A, Zhang M. Lower limb muscle co-contraction and joint loading of flip-flops walking in male wearers. PLoS One. 2018;13(3):e0193653."

image and article source: http://lermagazine.com/issues/may/flip-flops-bare-feet-or-sports-shoes-which-are-best-and-which-are-worst