Foot core training to prevent running-related injuries. A survival analysis of a single-blind, randomized controlled trial

Key Points

1. Running-related injury risk was reduced in recreational runners who performed a foot strengthening protocol, compared to runners who did a placebo static stretching protocol.
2. This study was conducted in recreational runners and the generalizability to novice or elite runners requires further examination.

BACKGROUND & OBJECTIVE

Running is a popular recreational activity with recognised health benefits (1). However, running-related injuries are common and cause interruption or abandonment of physical activity. With incidence of running-related injuries reported to be as high as 79% (2), establishing effective injury prevention is a priority.

During running the foot plays an integral role in the absorption and transmission of body forces to the ground, and vice-versa. The intrinsic muscles of the foot are important contributors to foot function, assisting the dampening of impact forces and stiffening the forefoot for propulsion (3,4). Additionally, the intrinsic muscles provide the ability to actively modulate foot function to respond to varying demands (acceleration/deceleration, incline/decline) (5). Training these muscles may improve foot function and assist injury prevention in runners.

The aim of this randomized controlled trial was to investigate the efficacy of a foot muscle strengthening protocol in reducing the incidence of running-related injuries in recreational runners over the course of a 1-year follow-up.

Incidence of running-related injuries has been reported to be as high as 79%.

The idea that a stronger foot should better dissipate cumulative loads appears somewhat supported as foot strength gains were correlated with time to injury.

METHODS

118 participants (aged 18-55 years) who ran between 20 and 100km per week, for one year or more, were recruited for the trial. Key exclusion criteria were: a running-related injury in the previous 2 months, experience running barefoot or in minimalist shoes, previous lower limb surgery, and chronic diseases or impairments that could influence running performance.

Participants were randomized into one of two groups:

Group 1 - Foot muscle strengthening

• 8-week training protocol consisting of 12 foot-ankle exercises performed once per week supervised by a physical therapist, and 8 foot-ankle exercises performed 3 times per week at home with remote supervision.

Group 2 - Control

• 5-minute placebo static stretching protocol 3 times per week with weekly feedback from a physical therapist.

Following the 8-week intervention, participants were instructed to continue the respective exercises 3 times per week until the end of the 12-month follow-up and record their adherence. Weekly reports on running distance, pace and running-related injury incidence were completed. In addition, foot strength and arch index were assessed at baseline, 8 weeks and 16 weeks.

RESULTS

28 participants (23.5%) reported a running-related injury, including 20 participants (32.8%) from the control group and 8 participants (14.0%) from the foot strengthening group. Participants in the control group were 2.42 times more likely to experience a running-related injury than participants in the foot strengthening group in the 12-month follow-up (see Figure 1). Larger gains in foot strength over the 8 weeks of training was correlated to longer time to develop a running-related injury.

Adherence to supervised sessions was high (88%). Adherence to remote supervised (home) sessions was high in the first 8 weeks (90.4%) but declined over the 12-month follow-up (48.9%).

Other factors (previous injury, body mass index, foot strike pattern, sex, foot posture index, years of running, mileage and pace) did not affect running-related injury risk. However, each increased year of age was associated with a 1.07-fold increase in running-related injury risk.

LIMITATIONS

There was no differentiation between types or sites of running-related injuries. Foot strengthening may be more effective in preventing some injuries than others, but this could not be determined from this study. Running-related injuries were also self-reported which may have introduced some bias. Finally, the generalizability of results to novice runners (<1 year) with lower weekly mileage (<20km), or elite runners, is unknown.

CLINICAL IMPLICATIONS

This study employed rigorous methods, such as pre-registration and publication of the trial protocol (6), random group allocation, blinded assessments, monitoring of adherence to the intervention, and analysis of data using an intention-to-treat approach, which improves confidence that unbiased conclusions can be drawn from the data. The study protocol was published in an open access journal (6), making the detailed description of the exercise protocol freely downloadable to use.

The authors' proposition that a stronger foot should better dissipate excessive and cumulative loads appears somewhat supported as foot strength gains were correlated with time to injury. However, how each runner responds biomechanically to foot strength improvements and how this relates to different injury types or sites requires further investigation. Although age was the only independent risk factor identified in this cohort, other risk factors like body mass index, previous injury and mileage might still be important to consider. Selection bias (exclusion criteria used in recruitment) may explain why these factors weren't relevant in this group of runners.

The program structure included sessions supervised by a therapist (weekly for 8 weeks) as well as independent (home) sessions that were remotely supervised using a web program. All sessions were estimated to take 20 to 30 minutes to complete. This time commitment may be a consideration for implementation. The remote supervision involved contacting participants who failed to log in to the web software for more than five consecutive days, or if participants failed to attend any of the locally supervised sessions. The remote supervision (continued contact) may relate to the high adherence that was observed in the first 8 weeks of the trial and could be an important consideration when implementing an intervention like this in the clinical setting.

Although the intervention period was 8 weeks, participants were instructed to continue the exercises at home 3 times per week for the duration of the 12-month follow-up. This begs the question: Is 8 weeks of training sufficient to obtain a reduction in injury risk, or was continuation of the intervention an important component in the program's efficacy over the 12 months? The authors provided some insight to this question. They reported that by the fourth month of follow-up differences in cumulative running-related injury risk were evident between the two groups and suggested that just 4 to 8 months of the foot exercise regimen might be effective.

+STUDY REFERENCE

Taddei U, Matias A, Duarte M & Sacco I (2020) Foot Core Training to Prevent Running-Related Injuries: A Survival Analysis of a Single-Blind, Randomized Controlled Trial. Am J Sports Med, 48(14), 3610-3619.

SUPPORTING REFERENCE

1. Hespanhol Junior, L. C., Pillay, J. D., van Mechelen, W., & Verhagen, E. (2015). Meta-Analyses of the Effects of Habitual Running on Indices of Health in Physically Inactive Adults. Sports Med, 45(10), 1455-1468. https://doi.org/10.1007/s40279-015-0359-y
2. van Gent, R. N., Siem, D., van Middelkoop, M., van Os, A. G., Bierma-Zeinstra, S. M. A., & Koes, B. W. (2007). Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review. Br J Sports Med, 41(8), 469-480. https://doi.org/10.1136/bjsm.2006.033548
3. Kelly, L. A., Farris, D. J., Cresswell, A. G., & Lichtwark, G. A. (2019). Intrinsic foot muscles contribute to elastic energy storage and return in the human foot. J Appl Physiol (1985), 126(1), 231-238. https://doi.org/10.1152/japplphysiol.00736.2018
4. Farris, D. J., Kelly, L. A., Cresswell, A. G., & Lichtwark, G. A. (2019). The functional importance of human foot muscles for bipedal locomotion. Proc Natl Acad Sci U S A, 116(5), 1645-1650. https://doi.org/10.1073/pnas.1812820116
5. Riddick, R., Farris, D. J., & Kelly, L. A. (2019). The foot is more than a spring: human foot muscles perform work to adapt to the energetic requirements of locomotion. J R Soc Interface, 16(150), 20180680. https://doi.org/10.1098/rsif.2018.0680
6. Matias, A. B., Taddei, U. T., Duarte, M., & Sacco, I. C. N. (2016). Protocol for evaluating the effects of a therapeutic foot exercise program on injury incidence, foot functionality and biomechanics in long-distance runners: a randomized controlled trial. Bmc Musculoskeletal Disorders, 17. https://doi.org/10.1186/s12891-016-1016-9