PainSci summary of Kong 2009?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided at the bottom of the page, as often as possible. ★★★★☆?4-star ratings are for bigger/better studies and reviews published in more prestigious journals, with only quibbles. Ratings are a highly subjective opinion, and subject to revision at any time. If you think this paper has been incorrectly rated, please let me know.
When shoes wear out, the biomechanics of running do change. Just not much. Kong et al tested 24 runners before and after 200 miles of road-running in the same pair of shoes. There were a few minor changes: longer stance phase, less forward leaning, and less ankle flexion. However, hip and knee angles were unchanged.
It’s significant that the effects on gait were generally minor, of course, but note the lack of difference in knee angles particularly. Knees are the site of two of the most common runner’s knee injuries, both iliotibial band and patellofemoral syndrome. In general, forces and injury risks increase together with more movement — more bending puts more torque on joints. A deeper knee bend is more stressful than a shallower knee bend. If worn out shoes have no effect on how far knees bend as you run, they aren’t much cause for concern. Although there are surely other biomechanical factors involved in these injuries, it’s unlikely that they are affected much by the condition of your shoes, and it’s reassuring that the most significant factor in overall knee stress — degree of flexion — is probably entirely unaffected.
Also interesting: they compared kinds of shoes — air, gel, spring — and concluded “the adaptation strategies to shoe degradation were unaffected by different cushioning technologies.” So it makes no difference what kind of common cushioning method you have in your shoes — they all degrade and affect running about equally. A natural enemy of the salesman is science proving that there is no difference between products!
Reader T.R. (among several others) pointed out that “200 miles is pretty low on the replacement spectrum. Usual rule of thumb out there is to replace every 300-400 miles (500-700km).” That’s a great point — and it’s probably a serious weakness of this study. It may be that they simply didn’t go far enough. The biomechanical picture could be totally different after 400 miles, particularly given that there’s a good chance that shoe degradation starts slowly and then accelerates:
See, when it starts to fall apart, man it really falls apart
Like boots or hearts oh when they start, they really fall apart.
— The Tragically Hip, Boots or Hearts
Nevertheless, the precautionary principle applies, and I do still recommend replacing your shoes when they begin to show obvious signs of wear. The risk of running in decrepit shoes may be small, but there’s not much reason to take that risk — just the modest cost of buying shoes somewhat more often. It’s not like you weren’t going to buy new shoes eventually! On the other hand, this data makes it pretty clear that replacing shoes while they still look fine isn’t really going to make much of a difference.
~ Paul Ingraham
original abstract†Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
OBJECTIVES: In this study, the effect of shoe degradation on running biomechanics by comparing the kinetics and kinematics of running in new and worn shoes was investigated. Three types of footwear using different cushioning technologies were compared.
DESIGN: Longitudinal study.
SETTING: Pre- and post-tests on overground running at 4.5 m s(-1) on a 20-m laboratory runway; performance measured using a force platform and a motion capture system.
PARTICIPANTS: 24 runners (14 men and 10 women)
INTERVENTIONS: 200 miles of road running in the same pair of shoes. Within-group factor: shoe condition (new/worn); between-group factor: footwear type (air/gel/spring).
MAIN OUTCOME MEASUREMENTS: Stance time was calculated from force data. External loads were measured by maximum vertical force and loading rate. Kinematic changes were indicated by sagittal plane angles of the torso, hip, knee and ankle at critical events during the stance phase.
RESULTS: Stance time increased (p=0.035) in worn shoes. The torso displayed less maximum forward lean (p<0.001) and less forward lean at toe-off (p<0.001), while the ankle displayed reduced maximum dorsiflexion (p=0.013) and increased plantar flexion at toe-off (p<0.001) in worn shoes. No changes in the hip and knee angles. No between-group difference among the three footwear groups or condition by type interaction was found in any measured variables.
CONCLUSIONS: As shoe cushioning capability decreases, runners modify their patterns to maintain constant external loads. The adaptation strategies to shoe degradation were unaffected by different cushioning technologies, suggesting runners should choose shoes for reasons other than cushioning technology.
- “Heel-shoe interactions and the durability of EVA foam running-shoe midsoles,” an article in J Biomech, 2004.
These five articles on PainScience.com cite Kong 2009 as a source:
- PS Is Running on Pavement Risky? — Hard-surface running may be risk factor for running injuries like patellofemoral pain, IT band syndrome, shin splints, and plantar fasciitis
- PS Save Yourself from IT Band Syndrome! — All your treatment options for Iliotibial Band Syndrome reviewed in great detail, with clear explanations of recent scientific research supporting every key point
- PS Save Yourself from Patellofemoral Pain Syndrome! — Patellofemoral pain syndrome (aka runner’s knee) explained and discussed in great detail, including every imaginable self-treatment option and all the available scientific evidence
- PS Save Yourself from Plantar Fasciitis! — Plantar fasciitis explained in great detail, including every possible treatment option, and all supported by recent scientific research
- PS Save Yourself from Shin Splints! — Causes and treatment options for shin splints explained and discussed in great detail, especially shin pain caused by myofascial trigger points, compartment syndrome, medial tibial stress syndrome, and stress fracture
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- A Bayesian model-averaged meta-analysis of the power pose effect with informed and default priors: the case of felt power. Gronau 2017 Comprehensive Results in Social Psychology.
- The neck and headaches. Bogduk 2014 Neurol Clin.
- Agreement of self-reported items and clinically assessed nerve root involvement (or sciatica) in a primary care setting. Konstantinou 2012 Eur Spine J.
- Effect of NSAIDs on Recovery From Acute Skeletal Muscle Injury: A Systematic Review and Meta-analysis. Morelli 2017 Am J Sports Med.
- Association of Spinal Manipulative Therapy With Clinical Benefit and Harm for Acute Low Back Pain: Systematic Review and Meta-analysis. Paige 2017 JAMA.