Injury prevention: the Ys and wherefores of balance testing

During the test, it is the strength, balance and coordination of the stance leg that is being evaluated. The legs are then swapped over (ie stance leg becomes the reaching leg and vice-versa) and the test is repeated. The distances reached on each leg are measured, and used to calculate asymmetries between the left and right legs. The idea is to evaluate balance, strength, and mobility and potentially flag injury risk if there are significant asymmetries between the scores for the right leg and those for the left leg.

Is the Y-Balance test valid?

Although popular as a screening tool to predict injury risk in athlete, there’s much debate about how reliable and relevant the Y-balance test is. Some studies have suggested it has value, particularly in specific populations, whereas critics have argued that there are simply too many other factors that can impact injury risk (eg sport type, sex, training load, fatigue, previous injuries etc) to pin down a universal threshold for future injury risk.

A 2021 systematic review and meta-analysis study (a study that pools all the data from previous studies on a topic to come up with more robust conclusions) investigated the reliability of the YBT-LQ test to determine if and how performance scores on the test varies among different populations (ie sex, sport/activity, and competition level), and to determine whether asymmetry, individual reach direction performance, or composite scores were able to predict injury risk⁽⁴⁾.

Fifty-seven studies were included, with nine studies assessing test-to-test reliability, 36 assessing population differences, and 16 assessing injury prediction. The results showed that both the biological sex of the athlete and their sport affected the numerical scores achieved in the posterolateral (backward and outward) and posteromedial (backward and inward) parts of the test but not in the anterior (forward) part. Overall, these differences meant that it’s not reliable to calculate a threshold score for future injury risk unless there is gross asymmetry or that score has been developed for a specific group of athletes (eg female distance runners, male soccer players etc).

Male runners and the Y-balance test

With the above in mind, brand new research published earlier this month makes for very interesting reading if you are a male recreational runner⁽⁵⁾. In this study, researchers looked at the power of the Y-balance test for predicting a future plantar fasciitis injury in male recreational runners who were undergoing training in preparation for a marathon. Plantar fasciitis is a debilitating condition that causes pain and inflammation in the connective (fascial) tissues of the base of the feet, and is the third most common type of running-related overuse injury⁽⁶⁾.

To do this, 172 male recreational marathon runners underwent the Y-balance test and were then tracked and monitored for plantar fasciitis development during a 3-month follow-up period. Of the 172 participants, 12 (7% of the marathon runners) went on to develop the condition during the three months. Their baseline data from the Y-balance test were then compared to those of runners who remained uninjured. The key finding was that the asymmetry in the posterolateral reach (middle picture in figure 1) was very significantly greater in the injured runners than in uninjured runners. In fact, for every 1cm increase in the asymmetry between right and left legs in the posterolateral reach, the risk of developing plantar fasciitis was increased by 18.3%. Further analysis showed that more generally, across this cohort (male recreational runners), a posterolateral reach asymmetry greater than 4.5cm was a strong risk factor for the development of plantar fasciitis.

Implications for runners

In their conclusions, the authors recommended that male recreational runners (and those who coach them) should aim to try and reduce inter-limb asymmetry as part of an injury prevention and treatment strategy. And given the Y-balance test is a simple and repeatable way of measuring asymmetry, using it on a regular basis could be worthwhile, especially in sports such as distance running where repetitive movements performed with small imbalances in flexibility, range of movement or strength can lead to cumulative stress and injury over time. In the case of male distance runners, an inter-limb asymmetry of more than 4.5cm in posterolateral reach is definitely worth addressing as it appears to significantly increase the risk of plantar fasciitis. More generally, the Y-balance test is a useful identifier of asymmetry, which is particularly relevant in strength asymmetries, because it is known that when asymmetry become large (over 10-15%) there is likely to be a detriment to performance and an increased injury risk⁽⁷⁾.

When trying to reduce inter-limb asymmetry, the key is to undertake unilateral leg strength or flexibility training, where the left and right legs are trained separately. For strength, good examples of these include reverse dumbbell or barbell lunges, single leg presses, Bulgarian split squats. You can see these being performed in the three video clips below:

For some additional examples of good single leg exercises, watch this video clip:

In all cases, it is important to ensure that the range of movement you work through and the speed of movement are identical for both legs. You should also work your less dominant leg first, making a mental note of how many reps were achieved and then follow up with the dominant leg, but ensuring you perform only the same number of reps (not more). Over time, your leg strength will even out, which will hopefully reduce your asymmetry (and your injury risk). Which you can verify by repeating the Y-balance test at regular intervals!

References

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7.       J Sports Sci Med. 2021 Oct 1;20(4):594-617