Effect of Increasing Running Cadence on Peak Impact Force in an Outdoor Environment

Abstract

INTRODUCTION

Within the U.S., the number of people running for exercise has dramatically increased over the past couple of decades. In 1990, five million people annually were reported to complete a road race. Nearly 30 years later, that number has reported to be 17.9 million.¹ While this increase in recreational running has obvious health and wellness benefits for the general population, the relative risk of sustaining a running-related injury (RRI) should be considered. Lower extremity RRIs occur in an estimated 56% of recreational runners, with some suggesting this to be as high as 80%.^2,3

Since RRIs are so prevalent, it is important to consider which factors may influence risk. While there have been a variety of proposed mechanisms for RRIs, high impact loading is often considered to be a factor. Davis, Bowser and Mullineaux⁴ examined 240 runners over a two-year period and reported that impact loads were greater in those runners who experienced an RRI compared to non-injured runners. They subsequently recommended that interventions aimed at decreasing the impact loads may be an effective strategy for reducing injury.⁴ In a systematic review by van der Worp, Vrielink and Bredeweg,⁵ 18 studies were reviewed and showed that runners with higher loading rates were more likely to have injuries than those with lower rates.

Impact loads may play a large role in many RRIs; therefore, many clinicians and researchers have shifted their focus to remedies for reducing impact and loading rate as a form of injury prevention or to assist in return to running following injury. One method to alter such impact forces is to increase cadence. Increasing cadence while maintaining a consistent pace has been reported to be an effective way to immediately lower impact, thus reducing injury risk.^6–8

Many studies to date have primarily been conducted in a controlled, laboratory setting utilizing motorized treadmills. While treadmills have been shown to produce biomechanically similar running patterns, they have the potential for changing spatiotemporal patterns.⁹ Tao, et al.¹⁰ reported an increased cadence, and decreased stance and swing time duration, when running on a level or inclined treadmill compared to running outdoors. In addition, outdoor running may produce notable variations in pace, cadence, and/or stride length during distance running events, as opposed to the constant pace imposed by the use of a treadmill.¹¹ Therefore, to examine the efficacy of cadence manipulation used for recreational running in an etiologically valid scenario, how cadence influences impact forces should be evaluated within a natural outdoor running environment.

To produce a change in spatiotemporal gait parameters, a runner will require a feedback strategy to prompt an increase in cadence. The methods for administering such feedback include the use of concurrent (provided during a task) and terminal (provided at conclusion of task) feedback.¹² According to Broker, et al.,¹³ concurrent feedback is most effective for cyclical activities such as running and cycling. Such feedback, when provided in an auditory manner, produces the most desirable change in performance when provided immediately after the same event in each cycle of movement.^13,14 In other words, to promote immediate change in running performance, an auditory stimulus should be given for each step taken. Additionally, alternative forms of concurrent feedback such as a visual stimulus are not feasible to provide to a runner in an open, outdoor environment. Previous studies utilizing an audio metronome in a laboratory environment have demonstrated changes to cadence in runners with the use of an external auditory cue.^6,7 This simple feedback cue would be compatible for delivery by a wearable portable device such as a watch or smartphone used outdoors.

The purpose of this study was to examine the effects of increased cadence on peak impact force in an outdoor setting. It was hypothesized that an increased cadence would decrease peak ground reaction force. A secondary aim of this study was to explore the feasibility of using an auditory metronome as a stimulus cue to increase cadence during an outdoor run.

METHODS

RESULTS

Fifteen participants (8 females, 7 males) with a mean age of 23.5 years (range 22-26) completed both baseline and cadence sessions. The reported average weekly mileage was 16.5 miles. A repeated measures ANOVA revealed a 5.6% decrease in average peak force after cadence manipulation when compared to baseline (p<0.05) (Figure 1). Peak force decreases were found to have medium effect size (Cohen’s d=0.56) (Table 1). During both the baseline and cadence session runs there was no difference in peak force during the first mile compared to the second mile (p=0.202) and no interaction effect found between session and distance (p=0.13).

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Figure 1.

Mean and 95% Confidence Intervals for average cadence expressed in steps per minute (SPM) on one lower extremity throughout Mile 1 and Mile 2 for both Baseline and Cadence Tests during outdoor running

Mean and 95% Confidence Intervals for average cadence expressed in steps per minute (SPM) on one lower extremity throughout Mile 1 and Mile 2 for both Baseline and Cadence Tests during outdoor running.

Results from the two-way ANOVA demonstrated insole-measured cadence increased 7.3% from baseline to cadence sessions (p<0.001) (Figure 2). The effect size for the cadence increase was high (Cohen’s d=1.24) (Table 2). Average cadence was found to decrease from mile 1 to mile 2 by 0.56 steps per minute (p=0.032). However, there was no interaction effect found between session and distance (p=0.597).

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Figure 2.

Mean and 95% Confidence Intervals for peak vertical ground reaction force (vGRF) expressed in multiples of bodyweight (BW) between Mile 1 and Mile 2 for Baseline and Cadence Tests during outdoor running

Mean and 95% Confidence Intervals for peak vertical ground reaction force (vGRF) expressed in multiples of bodyweight (BW) between Mile 1 and Mile 2 for Baseline and Cadence Tests during outdoor running.

When comparing the average cadence measured by the insoles against the cadence measured by the GPS watch, the two-way ANOVA results revealed no difference in measurement between the devices (p=0.096), yet an overall increase in average cadence remained between sessions (p<0.001), confirming that both devices were able to detect a similar percent change in cadence from baseline to cadence sessions (Figure 3) (Table 3). No interaction effect was determined between session and distance (p=0.928).

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Figure 3.

Mean and 95% Confidence Intervals for average cadence expressed in steps per minute (SPM) on one lower extremity throughout Baseline and Cadence Tests. Data compared cadence measured between Garmin GPS watch (Watch) and Loadsol insole sensors (Insole) during outdoor running

Mean and 95% Confidence Intervals for average cadence expressed in steps per minute (SPM) on one lower extremity throughout Baseline and Cadence Tests. Data compared cadence measured between Garmin GPS watch (Watch) and Loadsol insole sensors (Insole) during outdoor running.

DISCUSSION

The purpose of this study was twofold: 1) to determine the effect of cadence modification on peak impact force during an outdoor run, and 2) to examine the immediate response and magnitude of cadence modification through the use of a metronome as an auditory stimulus during a second session. It was hypothesized that as cadence increased, peak impact forces would decrease. It was additionally hypothesized that use of a metronome would produce a higher cadence during the run.

In support of these hypotheses, participants demonstrated a substantial increase in cadence by 7.3% using a metronome for outdoor running with a concurrent decrease in average peak impact force by 5.6%. One possible explanation for this change in lower extremity impact could be due to a change in foot strike pattern that may occur from the manipulation of the spatiotemporal factors associated with gait, however this was not directly measured or quantified. Increasing cadence has been shown to promote a change from a rearfoot strike pattern to a mid- or forefoot strike, which may result in decreased vertical loading between 0.3-1.3 body weights (BW).^21,22 A change from rearfoot to forefoot strike may have other beneficial effects including decreasing knee joint contact forces by an average of 1.2 BW²³ and decreasing patellofemoral joint stress by an average of 27%.²⁴ However, a forefoot strike may increase stress and loading at the Achilles tendon, ankle, and plantar surface of the foot.^25–27 Therefore, the benefits of changing foot strike pattern may need to be considered alongside the potential negative effects when implementing a gait modification technique.

Because of the maintained running speed between conditions, these findings may also be partially explained by the relationship between cadence and stride length in running. Since running speed is a product of cadence and stride length, an appreciable change in cadence at a constant running speed should result in a proportional reduction in stride length as a typical change.²² Specifically, decreasing a runner’s stride length by 10% has been reported to have beneficial effects on knee kinetics, including decreased contact forces at the patellofemoral joint by an average of 14.9%, decreased loading rate by 13%, and decreased impulse per kilometer by 4.5%.^28,29

Participants in this study were asked to increase cadence by 10% and, on average, were able to achieve approximately 7% above their preferred. Yet, this change was sufficient to produce a decrease in peak impact force between cadence conditions. The results of this study support data reported by Heiderscheit, et al.,⁶ where both 5% and 10% increases in cadence decreased energy absorption required at the knee by approximately 20% and 40%, respectively, as well as decreased energy absorbed at the hip (by ~57%) with 10% increase in cadence. Other studies suggest comparable benefits at the patellofemoral joint, with an average of 14% lower contact forces,⁷ and at the foot, with a decrease in overall plantar loading between 2.4-8.0%.²⁶ Similarly, Willy, et al.³⁰ described changes in multiple lower extremity loading variables at just 7.5% increase in cadence. These changes included a decrease in average vertical loading rate by 17.9% as well as instantaneous vertical loading rate by 18.9%.³⁰ In contrast, Hobara, et al.³¹ reported a minimum of 15% increase in cadence to produce changes in lower extremity loading variables such as vertical loading rate and vertical impact peak. However, some have suggested increases above 10% may not be necessary to produce the desired lower extremity benefits and may negatively increase perceived exertion and metabolic cost during running.^6,30

The results demonstrated in the current study may have implications for using cadence modifications to reduce peak impact force as well as promote the suggested benefits on other lower extremity loading variables during an outdoor run. Previous studies had suggested high impact forces are associated with development of common RRIs, such as medial tibial stress syndrome,^32,33 Achilles tendinopathy,^33,34 plantar fasciitis,^33,35 and patellofemoral pain syndrome.^33,36 However, a prospective study by Szymanek, et al.³⁷ discovered no association between a runner’s preferred cadence and development of lower extremity overuse injuries. Additionally, a recent meta-analysis by Vannatta, et al.³⁸ reported a conflicting association between peak impact force and RRIs. In the same study, they reported limited evidence relating decreased step rate to increased risk of shin-related injuries.³⁸ Further investigation into the use of cadence modification for the treatment or prevention of pain and RRIs appears to be warranted as was suggested in their review.

Altering patient cadence with the goal of reducing impact forces may be feasibly accomplished in a clinical setting using a treadmill.^6–8 The results of the present study demonstrate that similar cadence modifications can be feasibly implemented within an outdoor setting with the use of wearable technology and metronome feedback. Cadence measured through the GPS watch device was similar to the insole-measured cadence, indicating this commercially available technology may provide an effective method for measuring running cadence during indoor or outdoor gait retraining. This may open opportunities to provide running with cadence training protocols to be used in an outdoor running environment. This may also be a beneficial adjunct to training for military personnel where it has been reported that 25% of male and 50% of female military recruits suffer an injury related to their training, with 60-80% of those injuries being considered an overuse lower extremity injury.³⁹ Since much of military training is completed in an outdoor setting, use of a metronome and GPS watch may provide a feasible alternative for in-field feedback and cueing of cadence.

CONCLUSION

Using a metronome to increase cadence in an outdoor setting may be an effective way to reduce impact forces during running in an outdoor setting. Furthermore, using wearable technology that can provide cadence feedback via auditory cues may produce changes to cadence outside of the lab. Participants were immediately able to make a 7% average increase in cadence within one session using a metronome, suggesting that this may be an effective tool for manipulating cadence during outdoor running. While further research is indicated to examine the cadence effects on RRI incidence and for “in the field” training, these findings demonstrate a possibility for cadence alterations to be feasible in outdoor settings.

References