The purpose of this study was to examine the efficacy of a gait retraining program designed to reduce lower extremity loading during running. The main feature of the program was multiple training sessions on a treadmill involving real-time visual feedback of tibial acceleration. In addition, it involved a gradual increase in running time and a gradual removal of the feedback. This program resulted in a reduction in all of the loading variables of interest (PPA, VILR, VALR, and VIP). Subjectively, all of the subjects reported that their new gait patterns felt natural by the end of the sixth session. More importantly, the changes brought about by the retraining persisted for at least one month.
The results of this study build on the results of the previous study by Crowell et al. (2010)
. In that study, a single gait retraining session using real-time visual feedback was conducted. The objectives were to determine whether subjects could reduce their lower extremity loading and maintain the reductions for a few minutes after the feedback was removed. In that study, the changes in PPA, VILR, VALR, and VIP ranged from +6% to −60%, −15% to −39%, −16% to −39%, and −6% to −30%, respectively. For the group of subjects in the current study, the reductions in PPA, VILR, VALR, and VIP fall within the ranges achieved in the previous study. Thus, gait retraining using real-time visual feedback of tibial acceleration appears to be effective in reducing lower extremity loading for up to one month.
The loading variables (PPA, VILR, VALR, and VIP) were chosen because they occur when the foot is impacting the ground during running (generally within the first 50 ms of stance). Increases in these variables have been shown to be associated with tibial stress fractures (Davis et al., 2004
, Milner et al., 2006a
). Following the retraining program, PPA, VILR, VALR, and VIP were within the range reported for normal subjects in other studies (Hennig et al., 1993
; Mahar et al., 1997
; Laughton et al., 2003
; Davis et al., 2004
; Milner et al., 2006a
). This indirectly suggests that the risk of tibial stress fractures was reduced for subjects in this study. However, prospective studies are needed to confirm this.
Attempts by others to reduce loading during running have included the use of cushioned shoes, foot orthoses and shock attenuating insoles. In terms of tibial acceleration, researchers have found reductions in PPA of roughly 11% (Milani et al., 1997
) to 20% (Butler et al, 2006
) when comparing different shoes. Reductions in PPA of 16% have been reported for subjects running with cushioned insoles compared to running with standard insoles (O’Leary et al., 2008
). In examinations of foot orthoses, researchers have reported reductions as high as 23% for VILR, 18% for VALR, and 10% for VIP when running with custom orthoses in running sandals (Mundermann et al., 2003
) or commercially available orthoses in military boots (Dixon, 2007
). However, reductions in PPA, VILR, VALR, and VIP achieved in the current study () were at least two times greater than those achieved through the use of cushioning shoes, foot orthoses, or shock attenuating insoles. This suggests that an individual’s ability to alter their own running mechanics may be greater than that of external devices such as shoes, orthoses, or insoles.
An important indication of learning is the retention of motor skills beyond the training period (Salmoni et al., 1984
). We found that the reduced loading noted after the retraining persisted at the 1-month follow-up. We postulate that this was due to the faded feedback design used in the current study. Subjects who receive intermittent or delayed feedback have been shown to perform better in the long-term than subjects who received continuous immediate feedback (Swinnen et al., 1990
; Winstein and Schmidt, 1990
). Removing the feedback is beneficial to motor skill learning because the subjects must rely on internal cues for performing correct motor patterns (Winstein, 1991
). While insignificant, there were small increases in some of the variables between the post-training data collection and the 1-month follow-up (). A continued increase in these values post-training might indicate that subjects may need more than eight retraining sessions, or that they may need periodic refresher training. A study with longer follow-up is currently underway to determine this.
Changing a runner’s gait to reduce the risk of a stress fracture may have unintended consequences such as increasing the chance of another kind of injury. For the subjects in this study, the gait retraining did not appear to cause any injuries. The subjects appeared to accommodate to the new gait pattern quickly, and the soreness that occurred during the retraining sessions did not last for more than a few sessions. In addition, no injuries were reported at the one-month follow-up.
Runners seem to be able to modify their gait without specific instructions on how to accomplish it. In this study, subjects were given the same instructions about running softer and keeping their PPA below the line on the monitor. As a result, they all achieved reductions in their PPA, VILR, VALR, and VIP. Some of the strategies used by the subjects may be more effective than others, and these strategies are being examined as part of a larger study.
One of the strengths of this simple retraining program is its applicability to a variety of settings. The required equipment (treadmill, accelerometer, computer, and monitor) is readily available and relatively inexpensive. Therefore, it could be easily implemented into physical therapy clinics, fitness centers, and military training facilities in order to assess and retrain individuals at risk for stress fractures.
The results of this study are significant in many ways. First, the reductions in PPA, VILR, VALR, and VIP achieved through retraining are, on average, greater than the reductions achieved through the use of cushioning shoes, foot orthoses, or shock reducing insoles. Thus, impact loading may be more effectively reduced with gait retraining than footwear and orthotics, which may be more cost effective in the long run. Reducing this impact loading may reduce the risk of stress fractures in runners and allow them to remain physically active, resulting in healthier lifestyles. In terms of the military, recruits who sustain stress fractures and exhibit high impact loading could undergo the retraining during their rehabilitation. This may significantly reduce their risk for re-injury and could significantly reduce the high cost to the military when a soldier is medically discharged. Future studies will be focused on the kinematic strategies used to reduce PPA, VILR, VALR, and VIP. In addition, the gait retraining program used in this study will serve as the foundation for future experiments with other feedback methods and training schedules. The long-term goal of this work is to use gait retraining as a means for preventing stress fractures. Thus, after the feedback method and training schedule are optimized, a prospective study with a large group of runners at high risk of stress fractures can be conducted. This would show the efficacy of gait retraining for the prevention of stress fractures.