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.
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.