SPB looks at recent evidence on how running gait characteristics can predict injury in recreational runners, and what this means for injury risk reduction
Running is widely known to be beneficial for general health, and while some runners train to compete in race situations, more runners are recreational - running mainly for health and fun, often completing just a few kilometres per training session
(1). However, despite the extensive health benefits that running brings, the risk of lower-limb injury is comparatively high. For example, in a 6-month study of 87 recreational runners, at least one lower limb injury was suffered by 79% of the runners during the observation period
(2). In another study of 583 habitual recreational runners, researchers found that over the 12-month observation period, 252 men (52%) and 48 women (49%) reported at least one lower-limb injury that was severe enough to affect running habits, resulting in a visit to a health professional, or requiring the use of medication
(3). Among the wider running population as a whole, research suggests that the risk of sustaining a lower-limb injury can be anything from one injury per 147 hours of training to as high as one injury per 17 hours of training
(1).
Identifying risk
Given the comparatively high rates of injury among runners, researchers have tried to identify the factors that increase injury risk. We know for example that non-elite runners are more likely to sustain an injury over a given period of time if they have had a previous running-related injury, are running more than 64kms per week, or if speed work and/or interval training forms part of the training protocol
(1,4). However, identifying these kinds of associations is a rather blunt tool for runners and their physios trying to avoid a future injury. Many runners with a similar training and injury history, and similar training protocols will experience different rates of injury going forward. In other words, these associations can tell us what factors might increase the risk but not
which runners performing the same training protocol are at more risk.
A number of more recent studies have taken a more analytical approach by comparing differences in various biomechanical measures in injured vs. non-injured runners. These include:
- Knee adduction (where the knees move towards the center line of the body during running gait) moments(5).
- Ankle eversion range of motion and ankle eversion velocity (see figure 1)(6).
- Hip muscle strength(7).
However, while providing useful information, comparing these aspects of movement in a cohort of injured subjects with those from a different cohort of non-injured runners is still less than ideal. One reason is that many of these studies looking at injured/non-injured groups of runners provide only ‘relative risk of injury’ data.
Figure 1: Ankle eversion (vs. inversion)
For example, a 2018 study on knee stiffness and injury compared injured and non-injured runners, finding that those with a high level of knee stiffness were 18% more likely to suffer an injury than those with low knee stiffness
(8). However, while informative, this figure gives little idea of absolute risk in a runner. If the risk of a knee-stiffness related injury is only one injury per 5,000 hours of running (ie miniscule), an 18% increase is still a miniscule risk overall. However, if it is as high as one in 20 hours, it’s a risk that is well worth addressing. A better approach is to take injury occurrence the same cohort of runners performing the same training over an extended period of time, and identify the key biomechanical factors that are associated with injury. This allows not only an absolute measure of risk, but also enables runners and clinicians to identify WHO is most susceptible to injury, and by providing suitable training interventions to help mitigate these factors, reduce the risk of injury going forward.
Cohort study
Although there is little data in the literature using the cohort approach, a study published last year by Swedish scientists provides a valuable insight into which biomechanical traits in recreational runners predict increased injury risk over a period of training time, how large that risk is, and the kind of interventions that might be helpful to reduce injury risk
(9). In this study, 224 runners were recruited from the Gothenburg Half Marathon e-mail lists, and were tracked for one year. To qualify for inclusion, all the runners needed to meet the following criteria:
- Aged between 18 and 55.
- No musculoskeletal injuries in the lower extremities six months prior to the pre-study baseline examination.
- An average weekly running volume of at least 15kms for the past 12 months prior to baseline examination.
- No orthopaedic insole use when running.
- Female runners not pregnant.
- Did not suffer from diabetes.
The baseline clinical examination and measurements consisted of the following:
- An assessment of joint ranges of motion, levels of muscle flexibility and any trigger points (a hyper-irritable spot within a muscle that can affect movement by keeping the muscle short and stiff) present.
- A biomechanical running analysis, which assessed lower limb running movement patterns.
- Isometric (static position) strength tests.
Following the baseline examination, participants were instructed to maintain their regular training habits and to report training characteristics and potential pain on a weekly basis, for a period of 52 weeks. At the end of the 52-week monitoring period, the incidence of running-related injuries (RRIs) – as diagnosed by a medical practitioner was recorded. To ensure consistency, RRIs were strictly defined as:
‘A running-related musculoskeletal pain in the lower limbs or back that causes a restriction on or cessation of running (distance, speed, duration or training) in more than 66% of all training sessions over two consecutive weeks, or in more than 50% of all training sessions over four consecutive weeks, or that requires the runner to consult a physician or other health professional.’
The findings
Over the course of the year, the runners averaged 25kms per week and a total of 85 injuries were sustained. When the data was collated, the researchers found that there were no associations at all between sustaining an RRI and excessive or restricted joint range of motion, excessive or restricted muscle flexibility or having painful trigger points. There were however two factors that were very significantly associated with sustaining an RRI:
- Lower limb movement patterns - in particular, the late timing of maximal ankle eversion correlated with 55 injuries in the cohort.
- Strength - weak hip abductor muscles in relation to hip adductors correlated with 57 injuries (see later). In simple terms, weak hip abductor muscles relative to hip adductor muscles means the outer thigh/gluteal muscles (muscles which help move the leg outwards, away from the center line of the body) are not sufficiently strong to balance the strength of the adductors (inner thigh muscles), which act to pull the leg inwards towards the center line of the body).
The finding of the association between a relatively late timing of ankle eversion and RRI might be an indication of insufficient neuromuscular activation of the tibialis posterior muscle (see figure 2). This muscle works during the ‘pronation’ phase of running gait
(9). The pronation phase of the running gait is where the foot rolls inwards to help reduce shock after landing. A poorly activated tibialis posterior muscle would encourage excessive pronation by not keeping this movement in check early enough.
Figure 2: Anatomy of tibialis posterior
View from behind the lower leg showing the full length of the muscle, with the tendon located on the outside of the heel bone.
Figure 3: Pronation and running gait
Some pronation upon foot strike is a natural part of the running gait, but if not kept in check, excessive pronation can occur, increasing injury risk.
While other researchers have suggested late ankle eversion is not always predictive of RRIs
(10), it would seem prudent that runners, their coaches and clinicians should pay extra attention to ensuring that late timing ankle eversion is not a issue. Where it exists the addition of exercises targeting and activating tibialis may well prove beneficial. An excellent and simple exercise to increase tibialis posterior activation is to perform double-leg heel raises whilst squeezing a tennis ball (see figure 4 for a description of this exercise). When performing this exercise, runners should pay particular attention to the lowering (eccentric) phase of the exercise in order to maximally activate fibre movement patterns during the pronation phase of running.
Figure 4: Double-leg heel raise
This exercise should be performed whilst squeezing a tennis ball in order to encourage better activation of tibialis posterior and correction of late rearfoot eversion. Emphasis should be placed on the eccentric (lowering) phase of the exercise.
Hip abductor strengthening
Reduced hip abductor strength was significantly associated with an increased risk of RRI in the study above, and this is a finding that has support elsewhere in the literature
(11). There are a number of exercises that can be used to develop hip abductor strength. However, those developing functional strength – ie mimicking the kinds of loading demands made when running – are particularly recommended. An example of these kinds of exercises are ‘dynamic hip control’ exercises, which integrate dynamic abductor and external rotator muscle control using functional movements such as a short hop and stop movement.
Here is one variant (see figures 5 and 6):
- Using a broomstick or light barbell on the shoulder, the athlete stands in front of a mirror with the weight on the opposite leg that is going to be targeted by this exercise. In the photos below the aim is to train dynamic control of the left hip (figure 5).
- The purpose of the broomstick is so that the athlete can view his/her ability to hold the pelvis in a neutral and horizontal position. If one side of the broomstick drops, it indicates they are losing their ability to maintain a neutral and horizontal pelvis.
- The athlete jumps from the support leg onto the opposite leg (figure 6). Upon landing the abductor and hip external rotator muscle complex are forced to contract to control the pelvic and hip joint position.
- It is important that the broomstick remains horizontal upon landing. This will indicate the athlete is able to ‘hold’ the pelvis neutral upon impact, and no that dropping of the pelvis occurs.
- This is also a motor control exercise, which requires repeat efforts (with rest periods) to ensure that every repetition is done perfectly.
- Once motor control can be maintained, it is then possible to load this exercise with a weight placed on the barbell on the side opposite to the side that needs to be trained.
In addition to helping develop functional hip abductor strength, this exercise can also be used a diagnostic tool. Athletes can perform the test on both left and right legs. If landing on either leg causes the broomstick to drop on that side, this indicates a relative hip adductor weakness.
Figures 5 and 6: The start/finish position of the ‘short hop and stop’ hip abductor strengthening exercise
In summary
New research indicates that in recreational runners running modest distances, the risk of sustaining an RRI over the course of a year is around 38%. The biomechanical factors that are significantly correlated with sustaining an RRI are late timing of ankle eversion (most likely as a result of reduced tibialis activation) and reduced hip abductor strength relative to adductor strength. Given that conditioning exercises can help to remedy these biomechanical traits, runners, clinicians and running coaches may find functional movement and strength screening beneficial as a way of preventing future injuries.
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