Craig Payne

University lecturer, runner, researcher, skeptic, woo basher, clinician

Nov 12, 2017
Published on:
2 min read

I was doing a live Facebook thing with Ian Griffiths last week answering questions. One of those questions was about what happened to this blog as I had not posted anything since September. It simply boils down to time. I have what I think are some important posts written in my head and just need to find time to put pen to paper (or finger to keyboard). Not a day goes by that something is not published that is blog worthy. Some are more important than others and some pique my interest more than others. I should be spending today recording videos, but a near fatal dose of man flu that I only just managed to pull through from has left me with a bad voice for that today. It was then timely that this turned up this morning.

What initially caught my eye was that it appeared to be a pretty comprehensive study in a high-quality journal and in the abstract, it reported that injury prevalence was 8% in the habitually barefoot group and 61% in the habitually shod group. A statistic like that is going to get my attention. As with a lot of things like that, all is not what it seems when you dig into the details. I will follow this one to see how far the critical thinking skills get displayed in social media (I think we know the answer to that). Here is the abstract:

Foot Structure and Function in Habitually Barefoot and Shod Adolescents in Kenya
Aibast, Herje; Okutoyi, Paul; Sigei, Timothy; Adero, Walter; Chemjor, Danny; Ongaro, Neford; Fuku, Noriyuki PhD; Konstabel, Kenn; Clark, Carol; Lieberman, Daniel E. PhD; Pitsiladis, Yannis MMedSci, PhD
Current Sports Medicine Reports: November/December 2017 – Volume 16 – Issue 6 – p 448–458
Habitually barefoot (HB) children from the Kalenjin tribe of Kenya are known for their high physical activity levels. To date, there has been no comprehensive assessment of foot structure and function in these highly active and HB children/adolescents and link with overuse injuries. Purpose: The aim of this research is to assess foot structure, foot function, injury and physical activity levels in Kenyan children and adolescents who are HB compared with those who were habitually shod (HS). Methods: Foot structure, function, injury prevalence, and physical activity levels were studied using two studies with equal numbers of HS and HB. HS and HB children and adolescents were matched for age, sex, and body mass. Foot arch characteristics, foot strength, and lower-limb injury prevalence were investigated in Study 1 (n = 76). Heel bone stiffness, Achilles tendon moment arm length and physical activity levels in Study 2 (n=62). Foot muscle strength was measured using a strength device TKK 3360 and heel bone stiffness by bone ultrasonometry. The moment arm length of the Achilles tendon was estimated from photographs and physical activity was assessed using questionnaires and accelerometers. Results: Foot shortening strength was greater in HB (4.8 ± 1.9 kg vs 3.5 ± 1.8 kg, P < 0.01). Navicular drop was greater in HB (0.53 ± 0.32 cm vs 0.39 ± 0.19 cm, P < 0.05). Calcaneus stiffness index was greater (right 113.5 ± 17.1 vs 100.5 ± 116.8, P < 0.01 left 109.8 ± 15.7 vs 101.7 ± 18.7, P < 0.05) and Achilles tendon moment arm shorter in HB (right, 3.4 ± 0.4 vs 3.6 ± 0.4 cm, P < 0.05; left, 3.4 ± 0.5 vs 3.7 ± 0.4 cm, P < 0.01). Lower-limb injury prevalence was 8% in HB and 61% in HS. HB subjects spent more time engaged in moderate to vigorous physical activity (60 ± 26 min·d−1 vs 31 ± 13 min·d−1; P < 0.001). Conclusions: Significant differences observed in foot parameters, injury prevalence and general foot health between HB and HS suggest that footwear conditions may impact on foot structure and function and general foot health. HB children and adolescents spent more time engaged in moderate to vigorous physical activity and less time sedentary than HS children and adolescents.

This was quite a complex study (it was actually two studies in one) and there is no way I can go through it all here (especially things like the cherry-picked literature review and double standards in how they use different references), so refer you to the full paper for those with access with your critical thinking hat on. Here, I will only comment on three things:

Firstly, and really disappointing given the huge effort the researchers put into this study to see that undone by what should have been picked up in the pre-publication peer review process and fixed then. For most of the statistics, the authors used a student t-test. They did multiple comparisons using that test. If you dredge the data enough in any study with multiple comparisons you will always find something that is statistically significant by chance. You can’t do that unless you do a Bonferroni adjustment for the p-value. This means that most of the statistically significant findings that they reported were not really statistically significant. That casts a huge shadow over the whole study.

Secondly, and the authors did point this out, the results (given the first point I just mentioned) are probably only applicable to the environment that they study was conducted in and the lifestyle of the population under investigation. We can only speculate how generalizable they are to those who don’t live in rural Kenya.

Thirdly, especially given my first point, is that the difference in the injury rate between the two groups was large. The lower-limb/back injury prevalence was 8% in the barefoot group and 61% in the shod group. Even given the multiple comparisons issues, that is still a big difference. Unfortunately, next to no information is given in the methods on how they determined this (it should have been); over what time frame they went back over, etc. I assume this was self-determined retrospectively with all the issues associated with recall bias etc. The mean age of the participants was around 15 years, so this could also be an issue. While I do accept that the injury prevalence does appear to be much lower in the barefoot group and that this is possibly one of the more important findings in the study, but just do not understand why that chose to provide so little information on this in the methods and results when they provided extraordinary details on some other parameters which were not that important. It makes it hard to believe, judge and accept the finding without those details.

Additionally, the p-value for the differences in the injury rate was 0.01, which given the multiple comparisons (first point above) and the need to do a Bonferroni adjustment, then that different is probably not statistically significant (but given that it is 8 v 61, that is surprising!)

Fourthly, (I know I only said three, but this is an extraordinarily minor point), I notice that there was one bunion in the barefoot group (at age 15!); and I thought shoes cause bunions … go figure.

As always, I go where the evidence takes me until convinced otherwise …. and due to the multiple comparisons (first point above) and the lack of information (third point above), I need more information to be convinced.