Barefoot running: biomechanics and implications for running injuries. Curr Sports Med Rep 2012

Abstract Despite the technological developments in modern running footwear, up to 79% of runners today get injured in a given year. As we evolved barefoot, examining this mode of running is insightful. Barefoot running encourages a forefoot strike pattern that is associated with a reduction in impact loading and stride length. Studies have shown a reduction in injuries to shod forefoot strikers as compared with rearfoot strikers. In addition to a forefoot strike pattern, barefoot running also affords the runner increased sensory feedback from the foot-ground contact, as well as increased energy storage in the arch. Minimal footwear is being used to mimic barefoot running, but it is not clear whether it truly does. The purpose of this article is to review current and past research on shod and barefoot/minimal footwear running and their implications for running injuries. Clearly more research is needed, and areas for future study are suggested

Midfoot Strikers Are Different from Forefoot Strikers, but Similar to Rearfoot Strikers

Category: Sports Introduction/Purpose: Rearfoot strike (RFS) patterns have an impact transient that is associated with running injuries. These transients are not present in FFS patterns. Midfoot strike (MFS) runners are often grouped with FFS runners in studies as they are both non-heel strike patterns and assumed to be similar. However, this has not been tested. Tibial shock (TS) provides a measure of impacts and can be easily assessed in the field. Therefore, the purpose of this study was to compare TS among differing footstrike patterns measured during a marathon race. We hypothesized that MFS would have greater impacts than FFS, but lower than RFS. We also aimed to examine how impacts vary across speeds. We hypothesized that impacts would increase with speed similarly in RFS, MFS and FFS. Methods: 224 healthy runners (119 M, 105 F; 44.1±10.8 yrs) running the 2016 Boston marathon volunteered for the study. Prior to the race, participants ran on a treadmill to determine their habitual footstrike pattern (169 RFS, 32 MFS, 23 FFS). On race day, they ran the course wearing an accelerometer strapped onto their right medial ankle. For this part of the study, the average of the peak TS recorded between the 5 km and 10 km point of the race. This region was used as it had a flat gradient. The peak TS was recorded for each footstrike and averaged over the 5 km distance. This value was compared between the three footstrike patterns using an ANOVA (p<0.05). A regression analysis was used to determine the interaction of FSP and speed for each FSP using individual marathon runner data points. An ANOVA (p<0.05) was used to assess significance of the regression. Results: TS in FFS runners was significantly less than in MFS (P=0.01) and RFS (P=0.01) runners. (Figure 1, top panel). There was no difference between RFS and MFS (P=0.49). When examining the relationship between TS and speed, a significant positive correlation was noted for RFS (p<0.00). and MFS (p=0.02), but not for FFS (p=0.82) (Figure 1, bottom panel). Conclusion: In contrast to common belief, MFS runners exhibit impacts that are like RFS runners, and both are higher than FFS runners. This suggests that MFS runners should be grouped with RFS runners, and not FFS runners, when assessing impacts. In addition, both RFS and MFS runners exhibited greater impacts as speed increased. However, FFS runners appear to be able to maintain lower impacts at faster speeds. This may be due to greater calf activation, mitigating the effect of increasing speed on impacts. This may offer protection from impact-related injuries in FFS runners

Forefoot Striking Is More Effective in Reducing Loadrates than Increasing Cadence in Runners

Category: Sports Introduction/Purpose: Vertical impact forces are highly influenced by the way the foot contacts the ground. These impact forces are associated with high loading rates which have been related to running injuries. As a result, clinicians have begun to use gait retraining interventions to reduce loadrates and prevent future impact-related injuries. Two types of gait retraining techniques have been promoted to reduce excessive running impacts. The first involves increasing cadence (CAD), or number of steps per minute, by 5-10%, thereby reducing stride length. The second type of gait retraining involves landing on the ball of the foot at ground contact, or using a forefoot strike (FFS). Both of these gait-retraining styles have been reported to reduce impacts, but they have not been compared with each other. Methods: 33 healthy runners (9M, 24F), running 5-15 mpw, with a rearfoot strike pattern with cadence < 170 steps/min were recruited. Subjects were randomly allocated to either FFS or CAD retraining. All subjects underwent an 8-session gait retraining program (over 2-3 wks) with auditory feedback on a treadmill. The CAD group ran to a digital metronome to increase cadence by 7.5%. The FFS group wore a wireless accelerometer that provided an auditory signal on footstrike pattern. A gait analysis was conducted at baseline, 1 wk, 1 month, and 6 months. Variables included vertical average and instantaneous load rates (VALR, VILR). A 2 x 4 repeated measures ANOVA was used to compare differences within and between the CAD and FFS groups at baseline, 1 week, 1 month and 6 months post retraining. For variables with significant interactions, simple main effects of group, as well as time were further explored using one-way ANOVA Results: There were significant interaction effects of time*group for VALR (p= 0.001), VILR (p=0.001) and foot angle (p< 0.001), but not cadence. For the simple main effects for the CAD group, VALR reduced by 14%, 7% and 16% at 1 week, 1 month, and 6 months post gait retraining respectively, compared with baseline (Figure 1). However, these reductions were not significant. For the FFS group, VALR was significantly reduced by 50%, 51% and 51% at 1 week, 1 month, and 6 months post gait retraining respectively. Interestingly, both the CAD and FFS groups increased cadence by similar amounts. Conclusion: Transitioning to a FFS pattern is significantly more effective than increasing CAD when reducing vertical loadrate (both VALR and VILR) is the goal. These changes persisted out to 6 months post gait retraining, suggesting permanence of the new pattern

The Relationship Between Vertical Loadrates and Tibial Acceleration Across Footstrike Patterns

Category: Other Introduction/Purpose: While the etiology of injuries is multifactorial, impact loading, as measured by the loadrate of the vertical ground reaction force has been implicated. These loadrates are typically measured with a force plate. However, this limits the measure of impacts to laboratory environments. Tibial acceleration, another measure of running impacts, is considered a surrogate for loadrate. It can be measured using new wearable technology that can be used in a runner’s natural environment. However, the correlation between tibial acceleration measured from mobile devices and vertical ground reaction force loadrates, measured from forceplates, is unknown. The purpose of this study was to determine the correlation between vertical and resultant loadrates to vertical and resultant tibial acceleration across different footstrike patterns (FSP) in runners. Methods: The study involved a sample of convenience made up of 169 runners (74 F, 95 M; age: 38.66±13.08 yrs) presenting at a running injury clinic. This included 25 habitual forefoot strike (FFS), 17 midfoot strike (MFS) and 127 rearfoot strike (RFS) runners. Participants ran on an instrumented treadmill (average speed 2.52±0.25 m/s), with a tri-axial accelerometer attached at the left distal medial tibia. Only subjects running with pain <3/10 on a VAS scale during the treadmill run were included to reduce the confounding effect of pain. Vertical average, vertical instantaneous and resultant instantaneous loadrates (VALR, VILR and RILR) and peak vertical and resultant tibial accelerations (VTA, RTA) were averaged for 8 consecutive left steps. Correlation coefficients (r) were calculated between tibial accelerations and loadrates. Results: All tibial accelerations were significantly correlated across all loadrates, with the exception of RTA with VILR for FFS (Table 1) which was nearly significant (p=0.068). Correlations ranged from 0.37-0.82. VTA was strongly correlated with all loadrates (r = 0.66). RTA was also strongly correlated with both loadrates for RFS and MFS, but only moderately correlated with loadrates for FFS (r = 0.47). Correlations were similar across the different loadrates (VALR, VILR, RILR). Conclusion: The stronger correlation between vertical tibial acceleration and all loadrates (VALR, VILR, RILR) suggests that it may be the best surrogate for loadrates when studying impact loading in runners

A Comparison of Foot Strengthening versus Minimal Footwear Use on Intrinsic Muscle Size and Strength

Category: Other Introduction/Purpose: The intrinsic muscles of the arch have been classified as the core of the foot. Intrinsic foot muscles (IFM) work as local stabilizers and extrinsic foot muscles (EFM) work as global movers to help control the pronation of the foot. These muscles prevent excessive strain of the MLA. Previous research has shown that strengthening IFM may reduce pain and improve function in people with plantar fasciitis. Additionally, habitual use of minimal shoes that lack support of the arch require greater demand on the intrinsic muscles. The purpose of this study was to determine the effectiveness of two different strengthening interventions on IFM and EFM size and strength. Methods: 57 healthy runners (avg 15-30 mpw) were randomly assigned to a foot strengthening (FS, n=19), a minimal shoe walking (MSW, n=19), or a control group (C, n=19). Baseline cross-sectional areas of abductor hallucis, quadratus plantae, flexor digitorum brevis, and flexor digitorum longus, and thickness of the flexor hallucis brevis, tibialis posterior, and tibialis anterior were obtained with ultrasound using a 10 MHz linear probe. Doming, great toe flexion and lateral toes flexion strength were also measured using a custom-built dynamometer. The FS group then underwent an 8 wk foot and ankle strengthening program. The MSW group progressively walked in minimal footwear from 2,500-7,000 over the course of 8 wks. All groups, including C, maintained normal running mileage in conventional footwear throughout the 8 wks. Size and strength measures were then repeated. A repeated measures ANCOVA with a post-hoc test was used to determine differences in size and strength between groups. Results: All muscles measured in the FS and MSW groups increased significantly in size from weeks 0-8. There were no changes in muscle size in the C group. The FS group experienced significantly greater size changes for the flexor hallucis brevis than the MSW group. All other changes in muscle size were not significant between the FS and MSW groups. The FS and MSW groups showed significant increases in strength in all 3 tests from week 0-8. Strength of the control group did not change at any time. The increases in strength in the FS and MSW groups were not significantly different than each other. Conclusion: Exercises that target the intrinsic and extrinsic foot muscles are effective in increased strength and size of the muscles. However, similar increases in strength and size can be obtained by progressive walking in minimal footwear. Combining both these approaches may have an even greater effect. Stronger feet may offer greater protection against overuse injuries such as plantar fasciitis

Midfoot Angle Changes During Running After an 8-week Foot Strengthening Program

Category: Other Introduction/Purpose: The arch has been referred to as the core of the foot. The arch’s structure, movement, and integrity during running gait largely depends on the function of intrinsic and extrinsic foot muscles. There are many injuries that can be associated with a dysfunctional medial longitudinal arch. Improving the strength of the foot muscles could help improve arch function during running. The purpose of this study was to compare changes in arch deformation after eight weeks in a foot strengthening exercise group (FS), a group walking in minimalist shoes (MSW), and a control group (C). Methods: 24 healthy runners (average of 15-30 miles/week, no experience with minimalist footwear) were randomly assigned to FS (n=9), MSW (n=7) or C (n=8). FS subjects followed a series of progressive exercises designed to strengthen the intrinsic and extrinsic foot muscles. MSW subjects walked in minimal footwear, increasing from 2,500 to 7,000 steps/day over an 8 wk period. All runners maintained their pre-study mileage in conventional running shoes throughout the 8-week study Three-dimensional motion analysis data was collected at the beginning of the study and after week 8. Passive-reflective markers were placed according to the Oxford Foot Model. Subjects ran at a self-selected pace on a treadmill while data were collected for at least 10 strides. Peak midfoot angles were extracted and averaged within each trial. Group means at week 0 and week 8 were compared using paired t-tests with alpha set at 0.05. Results: While all groups experienced a decrease in midfoot angle, only the FS group experienced a significant change (see table). These results suggest that the foot exercise intervention resulted in more arch control during running than the progressive walking in minimal shoes. Greater changes may have been found if the subjects progressively ran in the minimal shoes which would have placed greater demands on the arch musculature. Conclusion: Based on these data, it seems possible for patients to reduce the amount of arch deformation during running by using targeted foot exercises. This could help with patients who have overuse injuries associated with increased arch deformation. These results also suggest that foot strengthening may be an effective way to prepare for minimal footwear running