Stress fractures are among the most common overuse injuries that runners and military trainees sustain. The tibia is the most frequent site for stress fractures of the lower extremities. There are many risk factors for these injuries, including, running mechanics. If running mechanics can be modified, it may be possible to reduce an individual’s risk of a stress fracture. The overall goal of this study was to determine if a gait retraining program could reduce the lower extremity loading associated with the risk of stress fractures. In addition, a model of the tibia was developed in order to examine the effect of gait retraining on the internal loading of the tibia.

The first aim of this study was to determine if runners could use real-time visual feedback from an accelerometer to reduce their tibial acceleration, which is one of the variables associated with stress fractures. Five runners participated in the study in which they ran on a force-measuring treadmill with an accelerometer attached to their tibias during a single 30-minute session. The session was divided into warm-up, feedback, no-feedback, and cool-down periods. Four of the five runners were able to reduce their tibial acceleration. As a group, the subjects reduced the peak positive acceleration on their tibias by 26%. Although the only variable provided as feedback was tibial acceleration, three other variable that are associated with stress fractures also showed reductions. The average reductions in impact peak, average loading rate, and instantaneous loading rate were 16%, 18%, and 18%, respectively. It was concluded that real-time visual feedback of tibial acceleration could be used by runners to achieve short-term reductions in the lower extremity loading associated with stress fractures.

The second aim of this study was to determine if multiple training sessions would allow subjects to reduce their lower extremity loading and to maintain those reductions for one month. Ten subjects whose peak positive acceleration was above normal participated in a gait retraining program over a two-week period. Subjects ran on a treadmill and received real-time visual feedback from an accelerometer attached to their distal tibias. Over the course of the retraining sessions, the running time increased and feedback time decreased. After the retraining sessions were completed, peak positive acceleration, vertical force loading rates, and impact peak were reduced approximately 50%, 30%, and 20%, respectively compared to their pre-training values. These reductions were also maintained at the 1-month follow-up.

The third and final aim of this study was to determine if the reduced lower extremity loading associated with the gait retraining program resulted in reductions in the loading on the tibia itself. This was assessed by examining the stresses, strains, and strain rates on the tibia. Simple beam models of the tibias of five of the subjects in the retraining study were created. Pre-training and post-training kinematic, kinetic, and electromyographic data collected from the subjects. These data were used to estimate the muscle forces, joint reaction forces and moments, and inertial forces and moments that were entered into the models. The models were used to calculate stresses, strains, and strain rates on the medial and posterior sides of the mid-tibia and the distal third of the tibia. All of the subjects reduced their pre-training strain rates on at least one location after completing the gait retraining program. For the group, the pre-training to post-training reductions in strain rate at the mid-tibia were between 13% and 23%. Also, at the distal third of the tibia, the mean reductions varied from 0.3% to 35%. These results suggest that tibial strain rates can be reduced by the gait retraining program. This is important because reductions in strain rates may reduce the risk of stress fractures for subjects who go through gait retraining. Further study is needed to examine the kinematic changes made by subjects as a result of the gait retraining. These changes need to be examined to determine if there is a relationship between specific kinematic changes and reductions in strain rates. In addition, more subjects are needed to determine if the reductions in strain rates are significant.

These studies are the initial efforts to examine the effectiveness of gait retraining as a means for reducing the risk of stress fractures. Future efforts will involve continued evaluation of the retraining program, new applications for the model, and eventually, retraining programs outside the laboratory. Continued follow-up of subjects is needed to determine the persistence of the reductions in lower extremity loading. The simple beam model can also be used to examine stresses, strains, and strain rates for data collected under various other conditions of speed, slope, fatigue, and footwear. Prospective studies are needed to determine if the gait retraining program can reduce the occurrence of stress fractures. If the retraining program can reduce the occurrence of stress fractures, it may be beneficial to establish gait retraining programs in physical therapy clinics, fitness centers, and military training facilities as a means of preventing stress fractures.