September 2016

Step-rate manipulation and foot-strike pattern

9running-iStock_98053341In distance runners, step-rate manipulation of at least 10% above a runner’s preferred rate may be an effective clinical gait retraining method to decrease the severity of foot inclination angle at heel strike and possibly encourage a transition to a nonheel-strike pattern.

By Darrell J. Allen, PT, DPT, MS, SCS, CSCS; Hollie Heisler, PT, DPT; and Jennifer Mooney, PT, DPT 

The popularity of running in the US is at an all-time high. With the growing number of runners, especially those running high mileage in preparation for half and full marathon distances, injuries related to running have also been on the rise. In a 2007 systematic review, Van Gent et al reported an incidence of running-related injuries ranging from 19.4% to 79.3%.1 As more runners seek care for running-related injuries, it becomes increasingly important that healthcare and rehabilitation professionals are equipped to provide care specific to these injuries.

In recent years, researchers have examined the impact forces associated with running and have shown—or at least provided a theoretical basis to suggest—that higher impact forces are a potential cause of various running-related injuries.2-4 It’s well established that impact forces at the knees and hips are typically higher in runners who use a rearfoot-strike (RFS) pattern than those who use a midfoot- or forefoot-strike pattern.5-8 Research also shows shod runners typically strike with the heel first, while barefoot runners tend to run with a nonheel-strike pattern. Changing foot-strike pattern from a RFS pattern to a midfoot- or forefoot-strike (FFS) pattern through gait retraining may be one way to reduce impact forces and the risk of running-related injuries.9,10 Up to 96% of recreational runners who run in traditional running shoes have been reported to be heel-strikers, making this a relevant issue for rehabilitation professionals.11,12

Gait retraining

Several methods of running-gait retraining to modify foot-strike pattern have been examined in the literature.13 Barefoot running has been one of the most prominent methods to accomplish a change from a RFS pattern to a FFS pattern. It has been well documented that barefoot running tends to support a more forefoot-based foot-strike pattern, decreased contact time, and a quicker step rate compared with running in traditional cushioned shoes, which tends to support a heel-strike pattern.14-16 Hatala et al, however, found not all habitually barefoot people prefer running with a FFS pattern and that factors other than shoe preference may dictate foot-strike pattern.17 The feel and comfort of barefoot running is very different than running in shoes and may be difficult for many runners to get used to.

Increasing step rate is more likely to positively affect foot inclination angle than foot-strike pattern in habitual heel strikers who run in traditional cushioned shoes.

Minimalist shoes have become popular in recent years, and marketing of these shoes has suggested their benefits to runners are similar to those of barefoot running. Rice et al in 2016 examined the component and the result of ground-reaction forces and instantaneous load rate during running in three groups of runners: habitually shod runners with a RFS pattern, habitually shod runners with a FFS pattern, and those who habitually run in minimal shoes and have a FFS pattern. The results suggested running with a FFS pattern in standard shoes resulted in similar load rates as running with a RFS pattern in standard shoes. However, resultant load rates were significantly lower when running with a FFS pattern in minimal shoes.18 It may be expected that those individuals who are not already FFS runners may experience higher load rates, at least initially, if they transition to minimalist shoes.

Other research has shown runners who switched to minimalist shoes did not acutely change their foot strike pattern from a heel-strike pattern to a nonheel-strike pattern and, in fact, experienced higher loading forces than when running in traditional shoes.19 Bergstraa et al reported increased plantar pressures in women who ran in minimalist shoes and no difference in landing patterns between running in minimalist versus traditional shoes.20 Finally, a study by Kernozek et al in 2014 looked at loading in minimalist footwear over a four-week period compared with one session. They also found higher plantar pressure loading in minimalist shoes, with the specific location of the higher pressures dependent on foot-strike pattern.21

running-table1These findings collectively suggest that runners who wish to continue to run in traditional running shoes may need to look at other methods of changing their foot-strike pattern to reduce impact forces.

Step-rate manipulation was described by Heiderscheidt et al in 2011; they found a significant reduction in impact forces in distance runners with as little as a 5% increase in step rate.4 Multiple authors have also reported a reduction in impact forces through increased cadence or step rate.6,22-24 The research by Heiderscheidt et al showed increasing step rate in shod runners was associated with reduced kinematic variables, including step length, center of mass vertical excursion, and foot inclination angle. Reduction of these variables was associated with decreased impact forces, which could theoretically reduce injury risk for distance runners.

Step-rate manipulation has also been presented as an easy and practical method of running-gait retraining in the clinical environment, since it can be accomplished using metronome cues and faded feedback methodology. While past research has documented many positive changes in running kinematics related to step-rate manipulation, it had not been examined as a method to change foot-strike pattern, nor had the percentage of step-rate increase needed to make this change been established.

Our research

The purpose of our study was to examine step-rate manipulation as a potential method to change foot-strike pattern from a heel-strike to a nonheel-strike pattern. A secondary purpose was to describe the effect of step-rate manipulation at specific percentages above a runner’s preferred step rate on foot inclination angle at initial contact.

We measured foot inclination angle, using the Medical Motion Video Analysis Software, as the angle between the treadmill and the sole of the foot, consistent with previous studies that have reported on this measure.5,29

Our study had 40 volunteer runners who were heel-strikers and had a weekly mileage of at least 10 miles. All were analyzed while wearing their own traditional running shoes. We confirmed runners as heel strikers during the warm-up periods on the treadmill. Although six runners claimed to be midfoot strikers on the day of testing, we confirmed on review of the data that they were heel-strikers. Each participant’s step rate was determined at his or her preferred running pace, and a metronome was used to increase step rate above the preferred rate by 5%, 10%, and 15%; these conditions were randomized.

We used 2D video motion analysis to determine foot-strike pattern and measure foot inclination angle at initial contact during running for each step-rate condition. We classified foot-strike patterns into three categories consistent with Lieberman et al: rearfoot, when the heel is the first region to contact the ground; midfoot, when the heel and ball of the foot simultaneously contact the ground; and forefoot, when the ball of the foot contacts the ground before the heel.14 We looked at foot strike during one segment of the run, not throughout the entire run.

Our study showed there was an overall difference and a significant, increasing number of nonheel strikers as the step rate increased: The preferred rate + 15% had significantly more nonheel strikers than the preferred rate and preferred rate + 5% conditions; the preferred rate + 10% condition had significantly more nonheel strikers than the preferred rate. Table 1 compares all three foot-strike patterns at the different step rates.

Our study also found a statistically significant reduction of the mean foot inclination angle as step rate increased (Table 2). The + 5% condition had a 3.34º smaller angle on average than the preferred step rate. The angle in the preferred rate was significantly greater than all other conditions, while the + 15% condition had a significantly smaller angle than all other conditions.

running-table2In summary, with regard to both the foot-strike pattern and foot inclination angle analysis, significant changes were associated with increases in step rate. For the foot-strike pattern, an increase of at least 10% in the step rate was needed to show a significant increase in the number of nonheel strikers. For foot inclination angle, significant decreases in the angle were observed with even 5% increases in step rate.

Clinical implications

The intent of our study was to determine whether step-rate manipulation alone was enough to change foot-strike pattern in shod recreational distance runners. We found increasing step rate above the runner’s preferred rate by 10% was successful in changing foot-strike pattern from a heel-strike to a midfoot- or forefoot-strike pattern in 17.5% of the runners, while increasing step rate by 15% changed foot strike pattern in 30%. These results suggest step-rate manipulation alone may be an effective way to change foot-strike pattern in a small percentage of shod distance runners.

Although this is a statistically significant change, it does represent a relatively small percentage of the overall population. The majority of the runners in this study continued to run with a heel-strike pattern under all step-rate conditions. This suggests step-rate manipulation may be helpful to change foot-strike pattern in a small percentage of shod recreational runners, but that other methods of changing strike pattern may be more effective for runners as a population.

One of our observations, though not statistically analyzed, was that many runners who changed foot-strike pattern had a very small foot inclination angle at initial contact at their preferred step rate. These individuals may have an easier transition to a midfoot- or forefoot-strike pattern with an increased step rate than those who foot strike with a larger angle of inclination.

A limitation of our study was that it was performed for just one training session and the participants did not have a chance to practice running at these step rates. It may be that step-rate retraining may be more effective in changing foot-strike pattern over a longer period, including in those individuals who have larger foot inclination angles at initial contact.

Another finding of our study was that the foot inclination angle significantly decreased as step rates increased, which supports results of past research.7 Others have shown that, as foot inclination angle decreases, ground-reaction forces and knee joint loads at initial contact are reduced.25 Our findings suggest, then, that reducing foot inclination angle by increasing step rate at least 5% above a runner’s preferred rate may have beneficial effects on impact forces, potentially reducing injury risk.

Our findings also suggest increasing step rate is more likely to have a positive effect on foot inclination angle than to prompt a change in foot-strike pattern in habitual heel strikers who run in traditional shoes. Clinical rehabilitation professionals can use step-rate manipulation above preferred to potentially change foot-strike pattern, but more likely to reduce the foot inclination angle or the severity of the heel strike in hopes of reducing impact forces and having a positive effect on injury rehabilitation or prevention.

Finally, we noted the 5% and 10% above preferred conditions were typically easy for the participants to match, and that only the 15% above preferred condition was an initial challenge for some participants. We agree with Heiderscheidt et al that the perceived increase in effort for the participants, especially at the + 15% condition, had more to do with attentional focus to achieve a novel task rather than a true increase in metabolic cost.5,27-29 This would suggest that, while increasing step rate above one’s preferred rate—especially at rates as high as + 15%—may  seem challenging at first, practice would reduce the attentional focus and perceived exertion.  Allowing step rate increases to be phased in gradually into the clinical environment would potentially help to reduce this change in perceived exertion for the runner.

Conclusions

Step-rate manipulation has been shown in the literature to be an effective means of reducing impact loading by changing sagittal plane variables such as stride length, center of mass vertical excursion, knee flexion angle at initial contact, and foot inclination angle.5,25,26 In addition, it’s also easy to implement in the clinical rehabilitation setting. For rehabilitation professionals seeking to reduce impact forces and rehabilitate or prevent running-related injuries, manipulating step rate can be done quickly with a simple metronome while an individual runs either on a treadmill or over ground.

Step-rate manipulation may be effective in changing the foot-strike pattern of recreational runners wearing traditional running shoes from a heel-strike to a midfoot- or forefoot-strike pattern, but probably in a relatively small percentage of runners. If changing foot-strike pattern is the primary goal, other methods may be needed.

The primary benefit of step-rate manipulation may be the reduction of foot inclination angle at initial contact, rather than a change in the actual foot-strike pattern. Step-rate manipulation of at least 10% above a runner’s preferred rate may be an effective clinical gait retraining method to decrease the severity of heel strike and possibly assist a runner to transition to a nonheel-strike pattern.

Darrell Allen, PT, DPT, MS, SCS, CSCS, is a clinical rehabilitation manager with Cleveland Clinic Rehabilitation and Sports Therapy and practices clinically at the Cleveland Clinic Twinsburg Family Health Center in Ohio. Hollie Heisler, DPT, is a senior physical therapist at Cleveland Clinic Rehabilitation and Sports Therapy Twinsburg Family Health Center. Jennifer Mooney, DPT, Cert MDT, is a senior physical therapist at Cleveland Clinic Rehabilitation and Sports Therapy Twinsburg Family Health Center.

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