Can barely handle going to the gym 3x/wk so no cardio for me. But if I wanted to get epic leans I'd do cardio 3 of the 4 days I don't train. Doing cardio in a gym is incredibly boring and seems to take forever so I prefer outdoors stuff. When I had to make weight I'd go from machine to machine. So I'd do the bike for about 8-10 minute, then do the rowing machine for 5 minutes, then the stairmaster for 5, the treadmill for 5, that Nordic ski type machine that part stair part pushing with your arms for 5, then back to the rowing... and just keep moving around like that. It goes much faster because once you are on a machine and get going it's time to move to another.