Unless there's some sort of resistance device attached to it, I'm not aware of how you'd increase your workload on them. I've never used them myself, but I seem to recall from my years and years of accumulated worthless knowledge that the primary benefits of roller use are developing smooth form (dished rollers were considered "cheating") and getting saddle time. That's why resistance trainers were able to hit it big in the market when they were first introduced. They filled a need that rollers weren't able to.