What you'll learn
- What a shoulder-fired weapon does to the people standing next to it, measured by gauges on their own helmets
- Which changes showed up within minutes, and which ones took two weeks
- Why the instructors told researchers more than anyone else
- The simple move on the range that cut one instructor's exposure the most
- What you can do between exposures
The instructor on a heavy weapons range has an unusual job. Traditionally they stand right at the gunner's shoulder while a Carl Gustav recoilless rifle, an AT-4 or a light anti-armor weapon goes off, and then they do it again with the next student, and the one after that. Over a two-year tour, a range safety officer supervises around 12 of these training events. Nobody walks off the range bleeding, and earlier studies of this kind of exposure were small and used different methods from one another. A team at the Uniformed Services University (USU) wanted to know whether all of that repeated low-level blast exposure still adds up.
Their results came out October 1 in the Journal of Neurotrauma, and the short version is that it does. Blast exposure during training was associated with measurable changes in memory, movement and blood markers, and the instructors, who were exposed the most, took longer to bounce back.
What the study did
INVICTA ran for five years and followed 224 people in four groups:
- 104 special operators firing live rounds in heavy weapons training
- 47 special operators going through the same training without firing live rounds
- 36 conventional active-duty service members with no blast exposure
- 37 instructors (range safety officers)
Everyone wore three small blast gauges, on the back of the helmet, on the chest and on the non-firing shoulder, which record every pressure wave that crosses them. Blast from these weapons can top 4.0 psi, which is the Department of Defense's interim guideline for when risk management has to kick in.
Researchers tested people before training, then at 30 minutes, 6 hours, 24 hours, 72 hours, 2 weeks and 3 months after. Instructors were also tested at 9 and 18 months, and after a training event at 18 months they went through the whole schedule again. So each person could be compared against their own baseline and against people who weren't exposed. The tests were practical ones: a word-list memory test where you hear 12 words and repeat back as many as you can, a stepping-in-place test with a phone strapped to the thigh to track gait, an eye-tracking headset, EEG for brain-wave patterns, hearing tests and blood draws.
What showed up, and when
Within minutes of training, the special operators showed changes in short-term memory, in the complexity of their EEG signals, and in blood levels of tau and UCH-L1, two proteins that come from nerve cells. Within hours, gait and eye movement had shifted too. USU described the gait change as a "robotic" walking pattern.
Some things took longer to appear. Two weeks out, more than 20% of the exposed group had a significant shift in at least one hearing threshold, and levels of another nerve-cell protein, neurofilament light, had changed.
Not everything moved. A blood marker called GFAP, blood-flow reactivity in the main arteries feeding the brain, and seven computer-based thinking tests showed no significant change. So a standard computer-based test on its own wouldn't have picked up what the memory and gait tests did.
Why the instructors matter most
Special operators go through heavy weapons training about every two years, and in the preliminary results most of them recovered fairly quickly. The instructors were different. Toward the end of their two-year tours, their memory and gait changes were bigger and lasted longer. When USU shared early results in 2025, lead investigator Dr. Michael Roy said instructors near the end of their tours were taking weeks, rather than days, to recover. "That's a pretty remarkable difference in terms of both the magnitude and the duration of the impact," he said.
Think about it this way. Walk across a lawn once and the grass is standing back up by the afternoon. Walk the same line every day for two years and you get a worn trail. Each step is no harder than the first one, but the grass needs much longer to come back, and the path keeps getting walked before it has the chance.
What the study can and can't tell us
The authors' own summary is careful: blast exposure during training "is associated with acute changes" in some blood markers and in brain function measures like short-term recall and gait, and "the effects appear to be short in duration, but recovery may be delayed after repeated exposure."
A few limits are worth knowing. Only the abstract is public right now, so we don't have the size of each change, and we're not going to guess at it. The instructor group was 37 people, which is small. The study tracked how people changed over weeks and months, so it can't tell us what these shifts mean years down the road. And nutrition wasn't one of the things the study tested, so it says nothing either way about whether diet or supplements change any of this.
One change that worked on the range
The study was already changing behavior before it was published. Roy told USU that instructors started stepping back from the gunner. One instructor standing shoulder to shoulder read 6 to 8 psi, nearly double the 4 psi guideline. One meter back, that dropped to about 3.5 psi. At three meters it was under 0.5.
What this means
If you or someone in your family works around repeated blast, or any job or sport where small repeated impacts add up, here's what we'd take from this:
- Distance counts. Follow your unit's guidance on positioning, because a few steps made a large difference on the gauges.
- Plan for recovery time. The study didn't test how to space exposures, but slower recovery after repeated exposure makes the days between range events worth guarding in your schedule where you can.
- Make sleep part of the plan, especially on the nights after range days.
- Eat real food. Regular meals with protein, vegetables and fatty fish like salmon or sardines give your body the raw materials it uses every day.
- Stay hydrated, especially on long range days.
- Talk to your medical provider if you notice memory, balance or hearing changes after training, and get your hearing checked on a regular schedule.
Repeated exposures add up, and the brain does its recovery work in between them. We built STATE as daily brain nutrition, one 2 oz shot with omega-3s, to support that recovery between exposures.
Sources
- Roy MJ, Keyser DO, Dovel M, et al. "Neurotrauma During Military Training: Results of the INVestigating traIning assoCiated blasT pAthology (INVICTA) Study." Journal of Neurotrauma, published online October 1, 2026. https://doi.org/10.1177/08977151261488794 (also at https://journals.sagepub.com/doi/10.1177/08977151261488794)
- Roy MJ, Keyser DO, Rowe SS, et al. "Methodology of the INVestigating traIning assoCiated blasT pAthology (INVICTA) study." BMC Medical Research Methodology, 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9746108/
- Brendel H. "INVICTA Study: Uncovering Blast Exposure's Impact on Special Operations Forces." USU News, April 10, 2025. https://news.usuhs.edu/2025/04/invicta-study-uncovering-blast.html
- Uniformed Services University publication record: https://scholar.usuhs.edu/en/publications/neurotrauma-during-military-training-results-of-the-investigating/
