You can't claim something unless it's been proven, or at least, you shouldn't claim something unless it's been proven or tested. You can't claim a helmet prevents concussive injury because you can't ethically make people fall of bicycles in a controlled, repetitive manner and then quantify the results; the way a scientific experiment would be carried out. You also can't use animal models because their heads are different shapes than ours...and, well, it should be obvious. What you can do is create models that approximate what could happen to our heads and use that info to provide evidence as to whether or not helmets increase safety and reduce instances of traumatic brain injury, like concussions, as seen here: Bicycle helmets are highly effective at prev... [Accid Anal Prev. 2014] - PubMed - NCBI