Mass huh. Interesting way of thinking about it. Though I would argue that strength and muscle tone are the important factors, not body mass. Technique is also critical. What snaps thin blades is torque along the handle to tip axis, or bending around an axis that runs from cutting edge to spine. As long as the user is using a technique which only applies stress directly from edge to spine with no twisting, even a very thin knife will successfully stand up to a large amount of force...

I propose that to be effective in using a knife, the user must have good amounts of at least two of:
- body (strength, tone, and dexterity)
- knife durability (high thickness, high mass)
- skill (methods, patience, intuition)

If you are not skilled, you require a lot of physical capability and blade durability to work well. If you do not have a durable knife, you require a lot of physical capability and skill. And if you lack physical capability, you need a brute of a knife and a lot of skill. The last statement is the weakest of the three, but it can be argued that manual dexterity is a bodily attribute closely related to muscle tone, and that without fine control over your movement you are more likely to apply inappropriate stress to the knife thus require the thickness. So being of low strength but excellent muscle tone and dexterity counts as being physically capable.

... I think I had a point somewhere along the way, let's see if anybody can find it in there.