Results of a recent experimental study challenge the widely-held belief that modern combat helmets are more effective at protecting soldiers against concussions. The research shows that helmets used during First World War without inner paddings may have an advantage in protecting soldiers’ brains from concussions when relying solely on cerebrospinal fluid. The present study explains this counterintuitive finding by revealing that while cerebrospinal fluid can prevent direct brain-to-skull contact during a single event, its protective capabilities diminish with each subsequent event occurring in quick succession—something conventional padded helmets appear to aggravate. The cerebrospinal fluid requires a certain amount of time to reset after an acceleration/deceleration event, which allows it to effectively provide cushioning for any subsequent events and protect against potential brain damage. However, an immediate occurrence of a subsequent event, when the fluid has no time to settle down, may significantly diminish the effectiveness of the fluid’s ability to provide adequate cushioning, thereby putting individuals at risk of serious injury. This new information may have implications for helmet design in the future and calls into question current assumptions regarding the best way to protect soldiers and athletes from concussions.

a slightly stronger correlation for healthy than diseased tissue (R 2 ¼ 0.692 vs 0.6387) (Fig 2). The circular variance of isolated media demonstrated a significantly lower correlation with Young's modulus (R 2 ¼ 0.3014). Under high-strain, oscillatory conditions, represented by the dynamic modulus E*, AA, TA, and TAA tissue collectively showed a moderate correlation with whole-wall circular variance (R 2 ¼ 0.2397), and a stronger correlation with isolated media (R 2 ¼ 0.331), whereas neither the whole wall nor media of abdominal aortic aneurysm tissue showed any correlation with E*.Conclusions: Our results provide evidence that under conditions of low strain, the tensile properties of the aorta arise from the vascular wall in its entirety, whereas under high strain conditions approximating physiologic stresses, the architecture of the media provides a relatively greater contribution. Furthermore, we have demonstrated that abdominal aortic aneurysm tissue, uniquely, demonstrates a lack of coherence between its biomechanical properties and histologic structure.