Introduction: Concussion due to sports-related collisions is a severe health challenge. Moreover, damage to the head and to the neck can sometimes lead to similar symptoms such as headache. Hence, to better prevent and diagnose concussion, we need to understand how helmeted impacts affect head and neck tissues. 
Methods: We simulated six impact conditions mimicking real-world relevant football collisions, with an impactor hitting a helmeted player to the frontal, lateral, rear, and vertical sites of the helmet and frontal and lateral sites of the facemask. The impact velocity was 6 m/s. Based on the simulations, we examined cumulative strain damage measure (CSDM) with the strain level of 20% in the whole brain and peak maximum principal strain (MPS) in the neck.
Results: For loads to the helmet, frontal impact induced CSDM20 of 0.08 to the brain, 0.45 to the upper cervical spinal cord, 0.59 to the disc and 0.11 to the facet joint. Lateral impact produced peak CSDM20 of 0.12 to the brain, 0.58 to the upper cervical spinal cord, 0.81 to the disc, and 0.25 to the facet joint. Rear impact caused CSDM20 of 0.15 to the brain, 0.49 to the upper cervical spinal cord, 0.50 to the disc, but very low 0.01 to the facet joint. Vertical impact induced low CSDM20 to the brain (0), but it induced high strain of 0.7 to the upper spinal cord, 0.50 to the disc, and 0.39 to the facet joint. For loads to the facemask, frontal impact caused CSDM20 of 0.01 to the brain, 0.48 to the upper cervical spinal cord, 0.66 to the disc, and 0.11 to the facet joint. Lateral impact to the facemask produced CSDM20 of 0.10 to the brain, and it caused MPS of 0.54 to the upper cervical spinal cord, 0.79 to the disc, and 0.10 to the facet joint.
Discussion/Conclusions: 
Brain strain distribution was highest during the rear impact to helmet, followed by the lateral impact to helmet, lateral impact to facemask, frontal impact to helmet, frontal impact to facemask and vertical impact to helmet.  The strain of the disc was high among all impacts, and both the upper cervical spinal cord and facet joint experienced the high strain during lateral and vertical impacts. These heterogeneous head-neck responses can help guide future protective gear development to reduce tissue strains, as well as assist in diagnosis for identifying regions of vulnerability during various impacts.
Acknowledgements: 
We acknowledge Western Engineering, Canada Research Chairs program and NSERC for support.

Analyzing head-neck tissue strains during football-related impacts