Increase bicycle resistance? I'm riding a lot with my girlfriend. We just ride - no training or such. Yet I do like to train. The intensity I normally ride with her is not enough for any training benefit. I guess adding weight could be an option, but the problem is that we sometimes go on long flat routes so the added weight would have to be uncofortably huge to compensate (I don't think carrying a bag of bricks is a solution). Using brakes all the time is tedious and potentially unsafe but also will produce uneven power outputs resulting in uncofortable speed changes, also using up brake pads swiftly. Is there a way to make pedalling less efficient without making rides too uncomfortable/unsafe?
Bicycle type is gravel 46-30 / 11-34 with a very relaxed geometry
Get a tandem. Wherever your relationship is going, it'll get there faster, and together, on a tandem.