The topic of the “drop” keeps coming up and has generated a lot of interest as well as the usual rhetoric and propaganda. It is defined as the difference between the heel and forefoot height of the shoe, which is more appropriately called the ‘pitch’, but the term ‘drop’, rightly or wrongly, has become the the popular term for this. I have previously commented on drop here, here and here. My conclusion from all that is that there is no evidence for any one particular drop having systematic benefits over another. The only argument for a ‘zero drop’ is the natural fallacy, but that is not evidence. Fan boys of ‘zero drop’, in response to me suggesting that there was no evidence even went as far as arguing, using the natural fallacy, that they should be allowed to use the natural fallacy… go figure that one out. The natural fallacy is not evidence! My conclusions at that stage from the previous research that is available on drop and running shoes and extrapolating from research on heel raises is that the response to a different drop is subject specific and there are no systematic responses. Now we have another new study to add to the mix and consider:
Shoe drop has opposite influence on running pattern when running overground or on a treadmill
Nicolas Chambon, Nicolas Delattre, Nils Guéguen, Eric Berton, Guillaume Rao
European Journal of Applied Physiology; December 2014
Minimalist running shoes are designed to induce a foot strike made more with the forepart of the foot. The main changes made on minimalist shoe consist in decreasing the height difference between fore and rear parts of the sole (drop). Barefoot and shod running have been widely compared on overground or treadmill these last years, but the key characteristic effects of minimalist shoes have been yet little studied. The purpose of this study is to find whether the shoe drop has the same effect regardless of the task: overground or treadmill running.
Twelve healthy male subjects ran with three shoes of different drops (0, 4, 8 mm) and barefoot on a treadmill and overground. Vertical ground reaction force (vGRF) (transient peak and loading rate) and lower limb kinematics (foot, ankle and knee joint flexion angles) were observed.
Opposite footwear effects on loading rate between the tasks were observed. Barefoot running induced higher loading rates during overground running than the highest drop condition, while it was the opposite during treadmill running. Ankle plantar flexion and knee flexion angles at touchdown were higher during treadmill than overground running for all conditions, except for barefoot which did not show any difference between the tasks.
Shoe drop appears to be a key parameter influencing running pattern, but its effects on vGRF differ depending on the task (treadmill vs. overground running) and must be considered with caution. Unlike shod conditions, kinematics of barefoot condition was not altered by treadmill running explaining opposite conclusions between the tasks.
Now that was interesting from two perspectives: the differences in the running shoe drop and the difference between overground and treadmill running.
To summarize, with regard to loading rates they found:
- in the overground condition, the higher drop shoe had the lowest loading rate. The barefoot condition had the highest loading rate.
- in the treadmill condition, the opposite was the case.
A couple of points can be made from this. This is yet another study that shows barefoot running has higher loader rates (in the overground condition – I will address the overground/treadmill difference below). If you are in the school that believes that impact forces and loading rates are important, then this is showing that a higher drop shoe induces a lower loading rate (however, the evidence on impact loads being important for injury is hardly compelling).
These findings (in the overground condition) is the opposite of what the rhetoric and propaganda says on ‘zero drop’ and loading rates when running barefoot.
To summarize, with regard to the kinematics at touchdown they found:
- in the barefoot condition, the foot/ground angle; ankle angle and knee angle were the same between overground and treadmill
- the foot/ground angle was higher during overground running in the shoe conditions compared to the treadmill condition
- ankle angle was higher (more dorsiflexion) overground running in the shoe conditions compared to the treadmill condition
- knee flexion angle was lower during overground running in the shoe conditions compared to the treadmill condition
The key point here is the differences between treadmill and overground. A number of people are automatically dismissive of any running research done on treadmills as it is not the same as overground and therefore research done using treadmills is not valid. This study would lend weight to view unless you are a runner that just runs on treadmills. I have never previously automatically dismissed studies just because they are on a treadmill. I prefer to look at what the research question is and what parameter(s) was under investigation and then look at what we know about that parameter(s)’s difference in overground vs treadmill running. A treadmill may be perfectly fine in some cases and not in others. The above study gives some good data on the differences between some parameters in overground vs treadmill running, so can be factored in the critical appraisal of running research done on treadmills.
Also of interest is the lack of difference in barefoot which would suggest that research on barefoot running in the parameters used in this study would be appropriate on a treadmill. We can only speculate as to why there were no differences in the barefoot condition. The authors did speculate that the sensory feedback during barefoot running could lead to less perturbation. I not so sure.
As always, I go where the evidence takes me until convinced otherwise, and this study shows:
- loading rates are higher in the barefoot condition during overground running
- the response to the drop in a shoe is different when running on a treadmill compared to overground
- there were not a lot of differences between the 0, 4 and 8 mm drop shoes
Chambon N, Delattre N, Guéguen N, Berton E, & Rao G (2014). Shoe drop has opposite influence on running pattern when running overground or on a treadmill. European journal of applied physiology PMID: 25501676