Is the drop of a running shoe associated with injury risk?

I previously blogged about the evidence on the use of zero drop vs a higher drop of running shoes and concluded that there is no evidence for one drop over another. Judging by the comments that the post received the ‘fan boys’ did not like that conclusion, responding with the usual rhetoric and propaganda and trope of logical fallacies. I could see nothing wrong with that conclusion as there was no evidence for any one particular drop over another. My own personal belief based on my understanding of the evidence and in my own experiences and my discussion with runners and running shoe retailers is that each individual runner does seem to have a drop ‘sweet spot’. There just seems to be a certain amount of drop that suits each individual runner that is usually found by trial and error. In other words its subject specific. For those not up to speed on terminology, ‘drop’ refers to the difference in the height of the shoe between the heel and forefoot. Typically a traditional running shoe has around 10mm. The ‘fan boys’ consider anything other than zero mm to be evil.

Having said that, things on the evidence front have just taken a turn:

Influence of the Heel-to-Toe Drop of Standard Cushioned Running Shoes on Injury Risk in Leisure-Time Runners
A Randomized Controlled Trial With 6-Month Follow-up

Laurent Malsioux, PhD, Nicolas Chambon, PhD, Axel Urhausen, Prof., MD and Daniel Theisen, PhD
Am J Sports Med August 8, 2016
Background: Modern running shoes are available in a wide range of heel-to-toe drops (ie, the height difference between the forward and rear parts of the inside of the shoe). While shoe drop has been shown to influence strike pattern, its effect on injury risk has never been investigated. Therefore, the reasons for such variety in this parameter are unclear.
Purpose: The first aim of this study was to determine whether the drop of standard cushioned running shoes influences running injury risk. The secondary aim was to investigate whether recent running regularity modifies the relationship between shoe drop and injury risk.
Study Design: Randomized controlled trial; Level of evidence, 1.
Methods: Leisure-time runners (N = 553) were observed for 6 months after having received a pair of shoes with a heel-to-toe drop of 10 mm (D10), 6 mm (D6), or 0 mm (D0). All participants reported their running activities and injuries (time-loss definition, at least 1 day) in an electronic system. Cox regression analyses were used to compare injury risk between the 3 groups based on hazard rate ratios (HRs) and their 95% CIs. A stratified analysis was conducted to evaluate the effect of shoe drop in occasional runners ( Results: The overall injury risk was not different among the participants who had received the D6 (HR, 1.30; 95% CI, 0.86-1.98) or D0 (HR, 1.17; 95% CI, 0.76-1.80) versions compared with the D10 shoes. After stratification according to running regularity, low-drop shoes (D6 and D0) were found to be associated with a lower injury risk in occasional runners (HR, 0.48; 95% CI, 0.23-0.98), whereas these shoes were associated with a higher injury risk in regular runners (HR, 1.67; 95% CI, 1.07-2.62).
Conclusion: Overall, injury risk was not modified by the drop of standard cushioned running shoes. However, low-drop shoes could be more hazardous for regular runners, while these shoes seem to be preferable for occasional runners to limit injury risk.

Nothing in the methods and analysis jumps out at me as being problematic and as this is a prospective randomized trial, then this is a high level of evidence. And, most importantly, the write up complied with the CONSORT statement.

Their conclusions were clear and supported by the data:
Overall, there were no differences in the injury rate between the different drops.
Low drop shoes increase the injury risk for regular runners (>6 months running).
Low drop shoes decreased the injury risk for occasional runners

As always, I go where the evidence takes me until convinced otherwise ….and zero drop is not a safe as its made out to be; but i still think there is a ‘drop’ sweet spot that is subject specific.

Malisoux, L., Chambon, N., Urhausen, A., & Theisen, D. (2016). Influence of the Heel-to-Toe Drop of Standard Cushioned Running Shoes on Injury Risk in Leisure-Time Runners: A Randomized Controlled Trial With 6-Month Follow-up The American Journal of Sports Medicine DOI: 10.1177/0363546516654690

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