iMG, HIA, HAE: what all the acronyms actually mean

Spend five minutes reading about smart mouthguards and you'll hit a wall of acronyms - iMG, HIA, HAE, CCC, PPV - thrown around like everyone already knows what they mean. Coaches nod along. Parents Google it later. Team doctors already speak the language, but the people making decisions on the sideline often don't, and that gap matters when the data is genuinely trying to keep an athlete safe.

So here's the plain-English version - the terms you'll actually run into, explained once, properly.

iMG - the thing itself

iMG stands for instrumented mouthguard - the clinical and research term for what most people call a "smart mouthguard" or, in the UK and Commonwealth, a "smart gum shield." All three names describe the same device: a custom-fitted mouthguard with a small sensor board built in, containing an accelerometer and a gyroscope. It looks and fits like a premium sports mouthguard. The difference is entirely on the inside.

What it actually measures

Every time an athlete's head is involved in a collision, the sensor board captures five things:

Linear acceleration - how hard the head was hit, measured in g-force (the same unit used for fighter pilots and astronauts).

Angular acceleration (also called rotational force) - how much the head spun, measured in rad/s². Emerging research suggests rotation is linked to concussion risk at least as strongly as a direct hit, sometimes more so.

Impact location and impact direction - where on the head the force landed, and which way the head was moving.

Impact count - a running tally, because the hits that don't make the highlight reel still add up.

HIA - what happens next

HIA stands for Head Injury Assessment - the structured clinical evaluation a medical officer performs once an athlete is flagged. This is the part worth being precise about: the mouthguard doesn't diagnose anything. It measures force and sends an alert. The HIA is where a clinician takes over. Since January 2024, World Rugby has required instrumented mouthguard data as part of the official HIA protocol in elite competition.

HAE - the term with two meanings

This is the one that trips people up, including inside the industry. HAE gets used two different ways:

Head Acceleration Exposure - the cumulative load an athlete absorbs across a session, week, or season.

Head Acceleration Event(s) - a single, countable impact (this is the sense used when a study reports, say, "17,000 head acceleration events").

Both are legitimate uses - they just mean different things, and it's worth checking which one a given article or study means before quoting a number.

The data terms - CCC and PPV

Two more you'll see in validation studies:

CCC (Concordance Correlation Coefficient) - how closely the mouthguard's readings match a calibrated lab reference sensor. Closer to 1.0 means better agreement.

PPV (Positive Predictive Value) - of everything the system flags as an impact, what percentage is a real impact rather than a false alarm like chewing or shouting.

Neither number means much in isolation. Both matter because they're how independent researchers - not manufacturers - decide whether a system's numbers can be trusted on a sideline.

Why this vocabulary is worth learning

None of this is academic for its own sake. A coach who knows the difference between linear and angular acceleration can have a more useful conversation with a team physician. A parent who understands that HIA is a clinical process - not something the mouthguard does on its own - knows what to actually ask about. The vocabulary isn't the point. Being able to act on what it describes is.

Want the full reference? Every term here - plus deployment studies, protocol names, and regional terminology - is in our complete Glossary, organized A-Z with a search box so you can look things up as they come up.