The response of the human body when subjected to a collision with a quantified delta - v and principal direction of force forms the bases for biomechanical analyses and occupant protection system performance in a motor vehicle collision. (expertreconstruction.com)
But this is not IHL (jus in bello) proportionalitybut the sort of proportionality we think of when applying the law of self defence in the jus ad bellum: does the overall amount or direction of the force used go beyond what would be needed to achieve the goal? (blog.politics.ox.ac.uk)
Though the size and direction of this force varies throughout the stroke, it can always be resolved into two components: one that pushes the boat forward and another that pushes it to the side. (newscientist.com)