I think just about any measure of cardiac performance could stratify people into high risk/low risk.
40 pushups in 30 seconds?
Running up 4 flights of stairs?
Cycling 10 miles in 30 minutes?
5 minute mile? 6 minute mile?
The firemen are an interesting group. I would think their average fitness is above average for the American population. But, still can be stratified into high risk and low risk individuals.