It seems a record is broken every year at the NFL Scouting Combine.
Players are bench-pressing more weight. They are running faster. They jump higher. No mark of physical achievement is static.
Except one.
The four-second 40-yard dash.
It is the man-lands-on-Mars challenge in football, one that may not be achieved for decades.
Even as players edge closer to it, you need only ask them if they think it's possible to understand the barrier the mark represents.
"I don't think so," said retired running back Chris Johnson, who ran a 4.24 40 in 2008.