My philosophy of pedaling is to always use the Goldilocks gear (which is continually changing with terrain) meaning you shift as needed to maintain a constant light pressure with a pedaling cadence that is comfortable. This means, assuming you are pedaling most or all of the time, that, going uphill but carrying momentum from the previous downhill, you would be shifting to lower gears one at a time, just before you need that lower gear. That works for me on rolling hills and mountains, and enables long rides without sore muscles. If you want to stand up and mash pedals in a higher gear, that will make you stronger but it takes repeated hill attacks and obviously, time to recover and develop that fitness. I don't want to stress my knees, so I am content with riding for endurance and stamina. My legs get tired but never sore, even after 60+ miles.