The Pain & Therapy Bibliography, Record ID 4242 {show all records}
Running in new and worn shoes: a comparison of three types of cushioning footwear
most detailed summaries by Paul Ingraham
summary
Running shoes certainly do wear out — for instance, midsole EVA foam steadily breaks down over time (see Verdejo et al). And when they do, the biomechanics of running do change. Just not very 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 it’s particularly important to 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 syndrome and patellofemoral syndrome. In general, forces and injury risks increase together when there’s greater movement in the joints — 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, it’s unlikely that there is much cause for concern. Although there are undoubtedly 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: Kong and colleagues also compared different kinds of shoes — air, gel and spring types — and concluded that “the adaptation strategies to shoe degradation were unaffected by different cushioning technologies.” In other words, 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.
Despite this, the precautionary principle applies here, 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.
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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.
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These four articles on SaveYourself.ca cite this paper as a source: