Troy assumes that your crankset has standard double chainrings, not a compact and not a triple chainring crankset. If you do have a triple, ECT doesn't want you to use the granny; only the big and middle rings. However...each of us has to listen to our own bodies and our own experience! If it's more comfortable for you to use lower gears, then by all means use them, and maybe later on you can start working up to riding higher gears. This time of year I start Troy's warm-ups and first set about one cog lower than what he says, then after I'm completely warmed up, I can ride all the gears as he calls 'em. If/when my bad knee is having a bad day, I just lighten up - exactly as us_wr suggests. Just experiment, try to set a goal and work toward it, but don't hurt yourself trying! And have fun!