If the Shoe Fits...
It is no surprise that running is one of the most popular leisure exercise activities globally. No fuss, no equipment required other than a pair of trusty ‘takkies’. But how important are the latter in determining our injury risk whilst running? Do we need expensive technical running shoes or are we ‘Born to Run’ without them? What factors should we consider when advising clients on how to make their next shoe selection? A brief glimpse at the literature suggests that one’s ‘comfort filter’ is as good a bet as any.
Running, in particular road running, places a highly repetitive strain on the musculoskeletal system. Consequently, the most common RRIs are overuse injuries (think of stress fractures, patellofemoral joint pain, iliotibial band syndrome, Achilles tendinopathy) that develop from the cumulative damage of multiple microtraumas to bone, muscle or tendon with inadequate recovery. Estimates of RRI prevalence are highly variable but recent reports suggest that a considerable 50 to 79% of runners will be injured during a calendar year! In an effort to understand their aetiology and implement evidence-based preventative measures, risk factors for RRIs have been thoroughly investigated[2,3]. Training-related parameters, including mileage, intensity and the relative weekly increase in these variables, have been most strongly implicated. Intrinsic and extrinsic risk factors (‘effect modifiers’) interact with the training variables to determine individual predisposition and susceptibility to injury respectively. The former may include anatomical aspects (e.g. bodyweight, high arches, leg length discrepancies, excess Q angle, gluteal weakness), biomechanical characteristics (e.g. impact force, rate of loading, moment about the knee joint, pronation) and prior injury, while the latter may include the climate and equipment (i.e. running shoes ) used.
Considering these numerous confounders, the aetiology of RRI is complex and it is not surprising that changes in one factor (shoe technology) have had no impact on RRI prevalence since the 1970s[1,3]. However, this should be viewed in the context of the recent boom in running popularity, and the different running demographic. As an illustration, between 1990 and 2013 the total number of road race finishers in the USA went from 5 million to over 19 million per annum, whereas in South Africa between 2009 and 2014, marathon running popularity increased by 59.4%. The running demographic has also changed considerably: whereas the 1970s witnessed comparatively few, dedicated runners who were lean and predominantly male, the contemporary ‘runners’ world’ has a female majority and sees all body types (particularly more overweight) taking to the streets. The queues of runners in the doctors’ rooms are thus that much greater. In line with such trends, the running shoe industry has experienced tremendous growth and competing brands are relentlessly innovating new technologies to suit different wakes of people, improve performance and reduce RRIs. Let’s explore how successful they have been in achieving the latter.
The biomechanical factors most commonly linked to RRIs are the high impact forces (‘impact transient’) characteristic of heel striking, and excess pronation (inward rolling) of the foot during the transition phase. Shoe manufacturers have attempted to counter these by constructing soft cushioned shoes with elevated heels (function as a shock absorber)[1,5,] and enhanced arch support to resist over-pronation[3,6]. However, there is no conclusive evidence (from albeit studies limited in sample size) that either of these factors has been associated with RRIs, motivating critical comments that the modern prescription of such running shoes has no scientific basis. For example, a 5-month prospective study showed no difference in injury risk between runners wearing shoes with soft midsoles and those wearing identical shoes with hard midsoles. Further, in a study of the kinetics and kinematics of runners wearing shoes when they were new and subsequently after 200 miles of road running, there was no alteration in the external forces experienced. Instead, it appears that neuromuscular adjustments to the perceived impact forces regulated the stress experienced by the body, such that the runners modified their kinematic patterns to maintain constant loads. This seems to emphasise the importance of progressive overload in relation to running volume and intensity. The musculoskeletal and neuromuscular systems need adequate recovery to adapt to the repetitive load of running as experienced with the current shoes.
Nowadays, shoe recommendations (neutral, anti-pronation, motion-control) are routinely based on a runner’s arch profile (neutral, flat or high), but is this practice evidence-based? In a “mythbusting review” by Nigg et al. (2015), the authors concluded that there is no definitive evidence linking foot pronation to RRIs. One of the largest studies reviewed by Nigg and colleagues was that conducted in 2676 military personnel, in which prescribing running shoes based on foot arch height had no influence on injury risk during basic military training. More running-specific evidence comes from two recent large prospective cohort studies have provided equivocal findings. Nielsen et al. (2014) provided 900 novice runners with neutral shoes for 1 year and found that foot pronation was not associated with RRI risk. In contrast, Malisoux et al. (2016) performed a blinded trial in which more seasoned runners (n=372) were randomised to either motion control or neutral shoes, and they found that that motion control shoes were protective against RRIs, but only in runners with pronated feet. Although the latter gives credence to arch-based guidance, further research is required to replicate these findings. The same authors have since investigated the influence of shoe ‘drop’ (vertical deviation between the heel and toe) on injury risk. Specifically, they randomised 553 recreational runners to identical shoes that only differed in drop-height (0, 6 or 10 mm), and after 1 year injury risk was similar between groups. Interestingly, when stratified according to running regularity, the 0 and 6 mm shoes benefitted more occasional runners but seemed detrimental to more regular runners. This finding may point to training errors again, specifically increasing mileage and/or intensity too rapidly in a novel shoe that places increased strain on the calf muscles and Achilles tendon. Similar errors have been consistently seen in individuals attempting the transition to barefoot running[1,12], which is a topic for the next issue of SSC. Regardless, further research is required to identify additional factors that influence the most suitable level of support, cushioning and drop height for each individual.
Ultimately, the nature of the contemporary running scene means that injury is inevitable. There is simply too much variation in training parameters, anatomy and biomechanics to completely isolate the influence of running shoes on RRIs. It is my opinion that were it not for the advancements in running shoe technology, injury rates would be significantly higher. At the end of the day, a simple yet intuitive approach to selecting a suitable running shoe may be purely based on ‘comfort’. One’s perception of comfort (‘comfort filter’) is one factor that has been associated with reduced injury risk[7,13]. Rather than focusing on generalised pros and cons of this gel or that foam, simply asking “what feels most comfortable” (not what has the best colour!) may be all that is required.
Tam, N., Wilson, J. L. A., Noakes, T. D. & Tucker, R. Barefoot running : an evaluation of current hypothesis , future research and clinical applications. 349–355 (2014). doi:10.1136/bjsports-2013-092404
Malisoux, L., Oestergaard, R., Urhausen, A. & Theisen, D. A step towards understanding the mechanisms of running-related injuries. J. Sci. Med. Sport 18, 523–528 (2015).
Nigg, B. M., Baltich, J., Hoerzer, S. & Enders, H. Running shoes and running injuries : mythbusting and a proposal for two new paradigms : ‘ preferred movement path ’ and ‘ comfort fi lter ’. 1290–1294 (2015).
Meeuwisse, W. H., Tyreman, H., Hagel, B. & Emery, C. A Dynamic Model of Etiology in Sport Injury : The Recursive Nature of Risk and Causation. Clin. J. Sport. Med. 17, 215–219 (2007).
Theisen, D. et al. In fl uence of midsole hardness of standard cushioned shoes on running-related injury risk. 371–376 (2014).
Malisoux, L. et al. Injury risk in runners using standard or motion control shoes : a randomised controlled trial with participant and assessor blinding. Br J Sport. Med 50, 481–487 (2016).
Richards, C., Magin, P. & Callister, R. Is your prescription of distance running shoes evidence-based? Br. J. Sports Med. 43, 159–162 (2009).
Kong, P. W., Candelaria, N. G. & Smith, D. R. Running in new and worn shoes : a comparison of three types of cushioning footwear. Br J Sport. Med 43, 745–750 (2009).
Knapik, J. J., Trone, D., Tchangja, J. & Jones, B. Injury-Reduction Effectiveness of Prescribing Running Shoes on the Basis of Foot Arch Height: J Orthop Sport. Phys Ther 44, 805–812 (2014).
Nielsen, R. O. et al. Predictors of Running-Related Injuries Among 930 Novice Runners: A 1-Year Prospective Follow-up Study. Orthop. J. Sport. Med. 1, 1–7 (2013).
Malisoux, L., Chambon, N., Urhausen, A. & Theisen, D. 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. Am. J. Sports Med. (2016).
Murphy, K., Curry, E. & Matzkin, E. Barefoot running: does it prevent injuries? Sport. Med. 43, 1131–1138 (2013).
Mundermann, A., Stefanyshyn, D. & Nigg, B. Relationship between comfort of shoe inserts and anthropometric and sensory factors. Med Sci Sport. Exerc 33, 1939–1945 (2001).