For athletes in contact sports, the danger isn't always a single, dramatic hit. Even smaller, repeated impacts—known as subconcussive head acceleration events—can affect the brain. A review of existing data shows that these repeated hits are linked to changes in brain microstructure, specifically in how water moves through brain tissue.
Researchers found that as the number of these minor hits increases over a season, certain markers of brain health, like fractional anisotropy, tend to decrease. Other markers, like mean diffusivity, show a positive link to the number of hits. These measurements help scientists see how the brain's physical makeup changes over time.
While the link between these hits and brain changes is clear, the data is still complex. Different ways of measuring these impacts show different levels of connection to brain changes. Because the results can vary depending on how the data is collected, these findings are currently used to help understand the risks of contact sports rather than providing a definitive rule for every athlete.
