It's simple, really. In feeders, you simply don't move your body around much. Almost the complete opposite of package car.
Most movement is in a spotter, which most sane feeder drivers avoid like the plague. Time DRAAAAGGs in a spotter. It is very easy work, no rush, BUT, nine hours in a spotter is like a weekend with the ex.
Local work (Pickups, railroad runs) is next, but is also slow work. AND, you tend to be driving your equipment in heavy traffic and next to moronic civilian drivers. Only difference is you get away from the yard.
A good road run is next. Not much movement on road runs, but the job is easy (weather permitting, of course), and time moves along nicely. You will be ok if you limit your calories, and join a gym or make a home workout program. This is what I do. I ate good in PC, and knew what was in store for me in feeders, so my diet was ready for feeders. But the lack of movement surprised me. For me, I didn't mind working out outside of work, but I also like to work 60 hours if I can. And the only problem with that is you are balancing working nights, figuring out your sleep and trying to fit your workouts in there somehow. If you get tired, guess which one gets the short shrift? Uh huh.
But sleeper team is the worst. For feeders, anyway. It's still light years ahead of any package car job, as far as hassle, workload and pay. The pay is the same as mileage, so it is better than any hourly feeder job. But sleeper teams define lack of movement. Drive, then get in the bunk. Exercise? Stretching your legs is your exercise in a sleeper team job. So you better have a mean ass degree of will power in your diet.
If I drove in a sleeper team, I would have to carry a dozen cans of chicken broth and a bag of turkey bones just to stay even on the scale. Oh yeah, you are gone all week in most sleeper jobs. It's a real hard job to stay married in. In sleepers, you are a legitimate, over-the-road trucker. You even have a big boy air horn, instead of a wimpy package car horn like the rest of us.
Where I'm at, most "B" drivers are low seniority drivers. It pays very, very well. Most jobs here pay each driver at least $2000 a week. And you almost never have to deal with the suits. But most of us would rather go home every night.
Just my two cents...