Y Balance Test (YBT): protocol, symmetry standards and injury risk

The Y Balance Test (YBT) is one of the most widely used dynamic balance tests in sports, especially for preventing ankle, knee, and hip injuries. It's the standardized, commercialized version of the Star Excursion Balance Test, designed to be quicker to administer and easier to compare between evaluators.

If you work with athletes returning from injury or want to catch asymmetries before they become a problem, this test should be on your radar.

What does this test measure?

The YBT measures dynamic balance in single-leg stance, assessing the ability to maintain postural control while the free leg reaches the maximum possible distance in three directions: anterior, posteromedial, and posterolateral. It combines mobility, strength, neuromuscular control, and proprioception of the standing limb.

Equipment needed

• A Y Balance Test kit (central platform with three graduated sliding tubes), or alternatively a tape measure and tape on the floor marking the three directions at 135° to each other
• A tape measure for leg length (from the ASIS to the medial malleolus)
• A recording sheet

Test protocol

1. Measure the leg length on each side (ASIS to medial malleolus) — this will be used to normalize the reach distance
2. The subject stands with the support foot at the center of the platform (or the central point of the tape markings)
3. With the opposite leg, they must reach as far as possible, pushing the sliding indicator (or touching the tape) in the anterior direction, maintaining balance without losing contact with the central foot
4. Repeat the reach in the posteromedial and posterolateral directions
5. Perform 3 attempts per direction and leg, recording the best score for each direction
6. Calculate the composite score: sum of the three directions, divided by (3 × leg length) and multiplied by 100, to get a normalized percentage

Common mistakes

• Not normalizing for leg length (which makes comparisons between people of different heights meaningless)
• Allowing the support foot to lift off center or lose contact during the reach (the attempt is invalid)
• Not allowing enough familiarization trials before starting to record

How to interpret the result

Data point	Reference / interpretation
Between-leg difference in anterior reach	> 4 cm has been associated with higher injury risk, especially in change-of-direction sports
Composite score (average %)	Values below ~89-94% (depending on sport and sex) are considered indicative of a dynamic control deficit
Overall limb asymmetry	Differences > 4% in composite score between legs are clinically relevant

Normative values vary quite a bit depending on sport, sex, and competitive level, so it's usually most useful to compare the subject to themselves (dominant vs. non-dominant leg, or pre/post injury).

Relationship with other tests

The YBT shares its foundation with:

• Star Excursion Balance Test (SEBT) — the original version with 8 directions, more thorough but also longer to administer
• Single-Leg Balance Test — a simpler preliminary test, useful if the YBT proves too demanding for the subject's level

Turn the YBT into a real tracking tool

The YBT generates quite a lot of data per session (3 directions × 2 legs × multiple attempts), and calculating the composite score and asymmetries by hand every time is tedious and error-prone. With Movalytics you can record the distances for each direction and leg, and the app automatically calculates the composite score and the between-leg difference, making it clear at a glance whether there's an asymmetry that needs attention.

Frequently asked questions

Do I need the official Y Balance Test kit to do it? It's not strictly necessary. You can replicate the protocol with a tape measure and tape on the floor marking the three directions, although the kit makes standardization and measurement easier. In which sports is this test most relevant? It's especially useful in sports involving changes of direction, jumps, and landings (soccer, basketball, volleyball, athletics), where dynamic control asymmetries are linked to knee and ankle injuries. How often should the YBT be repeated? In prevention contexts, every 8-12 weeks is reasonable. In rehabilitation processes, it can be repeated more frequently to monitor progress toward return to sport.