I would like to say that there are some selection effects at play here. This isn’t to say that more carries don’t lead to injury, it’s to say that the backs that get more carries don’t tend to get injured more. If you took a random player from the “low carry” group and gave him a Dickerson-like workload, he might snap in half within a month. Coaches, however, are very smart people who have access to lots of data and who get paid big bucks to know their players’ limitations, so when they give an RB a bunch of carries, that serves as a signal that the coach believes he can handle them.

I think this explains the career of a guy like Mewelde Moore. Moore was a backup for the Vikings and the Steelers, and every time injuries ahead of him pressed him into service, he always wound up outperforming the guys ahead of him on the depth chart… but he never got a starting job. In fact, I believe four different coaching staffs all had Mewelde Moore, and they all used him exactly the same way- change of pace back and emergency backup. The fact that those different coaching staffs all refused to give him a larger workload is indirect evidence that those coaching staffs, who all saw him in practice every day and had a good idea of what he was capable of, all agreed that he couldn’t handle it.

In other words, a large workload might wear a runner down, but you shouldn’t downgrade backs that receive a large workload under the assumption that they’re going to get worn down.