Functional Threshold Power: My FTP is fairly good according to my watch. My V02 max sux, though. I dont bike. Anyone know what FTP is exactly?

My FTP is fairly good according to my watch. My V02 max sux, though. I dont bike. Anyone know what FTP is exactly?

I struggle V02 Max as well as load, because the watch still seems to require me to run outside a lot. I am a gym rat.

But the FTP is good. I just dont know what it means.  Any help is appreciated.