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.
Parametric and bootstrap approaches to repeated measures designs