Answering that question definitively would take a large-scale study that follows hundreds of soldiers for years, and it is impossible to draw sweeping conclusions from a handful of cases. But the soldiers interviewed by The New York Times have experienced problems similar enough to suggest a disturbing pattern.
Most soldiers said they had fired at least 1,000 rounds a year in training, often in bursts of hundreds over a few days. When they were new at firing, they said, they felt no lasting effects. But with each subsequent training session, headaches, mental fogginess and nausea seemed to come on quicker and last longer. After years of firing, the soldiers experienced problems so severe that they interfered with daily life.
Nearly all of the soldiers interviewed for this article never saw combat, but they were nonetheless haunted by nightmares, anxiety, panic attacks and other symptoms usually attributed to post-traumatic stress disorder.
Nearly all sought medical help from the Army or the Department of Veterans Affairs and were screened for traumatic brain injury, but did not get a diagnosis. Instead, doctors treated individual symptoms, prescribing headache medicine, antidepressants and sleeping pills.
That is in part because of how traumatic brain injuries, known as T.B.I.s, are diagnosed. There is no imaging scan or blood test that can detect the swarms of microscopic tears that repeated blast exposure can cause in a living brain. The damage can be seen only postmortem.