Running injury prevention: why cadence matters

SPB looks at new research on ‘real world’ running injury risk and running cadence

There are good reasons why running is such a popular sport; it produces high levels of aerobic fitness in a time-efficient manner, it can be done anytime, anywhere, and it only requires a minimal outlay for equipment (just decent shoes needed). However, there is a downside for runners, especially who train and compete recreationally or at the amateur level, and that is the risk of picking up a running-related injury (RRI). Data shows that over the course of a year, lower extremity RRIs occur in an estimated 56% of recreational runners, with some studies suggesting this to be as high as 80%⁽¹⁾.

Risk factors for RRIs

Since RRIs are so prevalent in runners, it is important to be aware which factors may influence risk. There are a number of proposed causal factor for RRIs in runners, including a sudden increase in training volume or intensity, a change of running surface, incorrect shoe selection and biomechanical imbalances in runners themselves. Common to many of these factors is an increase in high-impact loading, and research suggests that high-impact loading is indeed a key factor in RRI risk.

For example, a 2016 study 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⁽²⁾. The authors went on to recommend that interventions aimed at decreasing impact loads may be an effective strategy for reducing injury in vulnerable runners. Meanwhile, in the same year, a systematic review looked at combined data from 18 studies on this topic⁽³⁾. It found that runners with higher loading rates were more likely to have injuries than those with lower rates.

Reducing high-impact loading

Given that the evidence for high-impact loading as a cause of RRI is robust, the obvious question is how can that loading be reduced? More cushioned shoes, shock-absorbing insoles and training on softer surfaces are all options, but all these types of interventions can end up altering a runner’s gait, which potentially brings a new set of problems. One method to reduce impact forces that is easy to implement is to increase running cadence (steps taken per second). If the speed is held constant, increasing cadence means that the stride length is reduced (since speed = stride length x cadence). Shorter stride lengths require lower levels of propulsion during push off, and produce less impact on landing.

Unsurprisingly therefore, increasing cadence while maintaining a consistent pace has been reported to be an effective way to immediately lower impact, thus reducing injury risk when running^(4-6). For this reason, many sports injury 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.

Real world studies

So far, so good. But there’s a problem with assuming that increasing cadence at a constant speed will automatically reduce RRI risk. Most of the studies on cadence, loading and RRIs carried out to date have conducted in a controlled, laboratory setting using motorized treadmills. While treadmill running results in biomechanically similar running patterns to normal outdoors running, these patterns are not identical, particularly when it comes to the timing of the different phases of the running gait⁽⁷⁾.

In particular, research shows that there is an increased cadence, and decreased stance and ‘mid-swing time duration’, when running on a level or inclined treadmill compared to running outdoors (see figure 1)⁽⁸⁾. In addition, outdoor running invariably produces significant fluctuations in pace, cadence, and/or stride length during distance running events, as opposed to the constant pace imposed by the use of a treadmill⁽⁹⁾.

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Figure 1: Running phases*

In treadmill running, mid stance and mid swing durations are shortened compared to outdoors running at the same speed.

*adapted from The Motion Mechanic - www.themotionmechanic.com/ 

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To try and confirm conclusively that increased cadence running really can reducing high-impact loading (and so reduce RRI risk) when running outdoors, newly published research by US researchers has investigated the effects of cadence on recreational and amateur runners performing natural outdoors running⁽¹⁰⁾. The scientists theorized that an increased cadence would decrease peak ground reaction force.

In addition, they also wanted to explore the feasibility of using an auditory metronome as a stimulus cue to increase cadence during outdoors running. Research shows that real-time auditory feedback is the most effective for regulating cadence⁽¹¹⁾ and that in the lab, using a metronome is particularly effective⁽⁴⁾. Therefore, they also tested out a simple feedback cue delivered by a wearable portable device such as a watch or smartphone used outdoors.

The research

In this study, 15 male and female adult recreational runners, running an average of 15 miles per week and with no current RRIs were recruited. Participants completed two separate 2.4-mile distance runs:

• Baseline – where they ran at their self selected pace and cadence. The metronome was turned off for this run and no mention of running cadence was given to ensure that the run was completed at their typical cadence.
• Cadence – where they ran at the same speed but with increased cadence of 10% over their baseline run directed by an audible metronome sound provided by the ‘MetroTimer’ app used on an iPod Touch to provide cadence cueing.

During both runs, Loadsol insole sensors were placed inside each participant’s typical running shoes bilaterally to measure peak force in Newtons (N) in both runs, and to allow an accurate comparison. The selected road course was a straight stretch void of turns, with minimal elevation change (less than 20 feet), and minimal traffic. The 2.4 mile distance was chosen for the run to allow for a comparison of miles #1 and #2 over time and to accommodate the acceleration up to a steady pace and acclimation to the auditory metronome. The actual running cadences were recorded by both the insoles and a GPS watch to ensure consistency and accuracy.

The findings

The first finding was that the audible cue using the metronome app was pretty successful at increasing cadence. On average, the runners increased their cadence by 7.3% in the ‘cadence’ run compared to the baseline run. Of more significance however was the change in peak ground reaction (impact) forces between the two runs. Compared to the baseline run at the runners’ usual cadences, the increase cadence run resulted in a significant drop of peak ground reaction forces of 5.6% across both miles of the run (see figure 2).

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Figure 2: Baseline vs. increased cadence run peak impact forces

Left = baseline run at normal cadence; right = cadence run at 7.3% higher cadence. Black bars denote mile #1; grey bars denote mile #2 in each run.

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Conclusions and practical implications

The first point to make is that the runners in this study were asked to increase cadence by 10%, but on average fell somewhat short, achieving just over 7% above their preferred cadence, even though they had the audible cue. This suggests that while simple in theory, increasing running cadence while maintaining the same speed (ie by reducing stride length) is not quite as easy as it sounds! Despite the shortfall in targeted cadence however, the 7.3% increase was sufficient to produce a very significant decrease in peak impact force between cadence conditions.

These findings (of reduced impact forces) are in line with previous research, which found 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⁽⁴⁾. They also tie in with other studies that found comparable benefits at the knee joint (with an average of 14% lower impact forces) and a decrease in overall foot loading of between 2.4-8.0%^(5,12).

Overall, these results suggest that increasing cadence while maintain normal training speeds is an effective way for educe impact forces during running outdoors, and so reduce RRI risk. Circumstances in which this approach may be especially useful include returning to running following an injury or simply as a way of inserting some low-impact runs in a training schedule. Using a wearable technology (smartphone app, MP3 player etc) providing an audible metronome appears to help runners achieve their increase cadence, but this study suggests that a bit of practice might be required to hit target cadence.

Athletes wishing to try this approach should first establish their normal cadence at a regular, moderate training pace (one that could be sustained for around an hour). To do this, an accurate step counter and a stop watch are required so steps per minute can be calculated. For example, if 1300 steps are recorded over a ten-minute run, the rate is 130 steps per minute. A cadence increase of 10% involves maintaining a step rate of around 143 steps per minute. This is what the audible metronome should be set at. It’s really important however that the running speed during an increased cadence run is NOT increased but held the same as in normal cadence training. This will involve a slight shortening of stride length. Simply increasing cadence without a corresponding shortening of stride length could actually increase impact forces – exactly the opposite of what is required!

References

1. Br J Sports Med. 2007;41(8):469-480; discussion 480
2. Br J Sports Med. 2016;50(14):887-892
3. Br J Sports Med. 2016;50(8):450-457
4. Med Sci Sports Exerc. 2011;43(2):296-302
5. Med Sci Sports Exerc. 2014;46(3):557-564
6. Sports Health. 2013;6(3):210-217
7. Sports Med. 2020;50(4):785-813
8. Int J Sports Phys Ther. 2019;14(5):731-739
9. J Strength Cond Res. 2014;28(5):1219-1225
10. Int J Sports Phys Ther. Aug 2021; 16(4): 1076–1083
11. J Appl Biomech. 1993;9(2):111-123
12. Int J Sports Med. 2014;35(9):779-784