The Smith machine gets a bad rap. Often referred to as the machine for lightweights, cop-outs, and Planet Fitness members, the reputation isn't ENTIRELY unearned. But there's one glute-firing exercise that's best left to this weight room main-stay.
My Sunday Funday typically consists of leisurely reading, a boardwalk stroll, and, more often than not, pizza. Because on the seventh day, SHE rests. But none of that gets underway until the yummiest part of my day is in the books: leg and glute accessory work at the recreation center. Tuesdays are for squatting and deadlifts at the commercial gym; the thrust is a must, and performed in the comfort of my own home on Thursdays, along with various band work; but Sunday...Sunday is sacred. This is when I get to do the really "fun" stuff - work that can't be classified under "functional" training or "big lifts." And quite a bit of it is performed on the lowly Smith machine.
Now, mostly EVERY lower body exercise one performs on the Smith machine can be carried out, and should probably be mastered with, a standard Olympic barbell or dumbbells - squats, deadlifts, lunges, Bulgarian split squats, kneeling squats, hip thrusts - the list goes on. For each one of those, however, I would still argue that they're worth performing on the Smith, too: when you're not focused on engaging your core, with a little care and proper cueing, you can focus more on firing the glutes. Play around with these variations and see for yourself.
But there's one move where the Smith machine trumps the barbell (because it would be impossible to perform) and free weights (awkward to execute) - and ankle weights, cables, and stationary machines too: the donkey kick. This video (not of me - the rec center has a strict "No Cell Phone" policy) shows it in action:
The set-up: yoga mat or other padding, smith machine, good knees.
Get onto hands and knees so that heels are close to underneath the bar when set to lowest height of Smith Machine. Hands should be lined up right under shoulders. Place one heel firmly on bar. While maintaining 90 degree angle in knee, flex foot and push the bar up and away from your body, firing the glute and pausing at the top. Repeat 10-12 times before switching legs, aiming to complete three sets on each leg. The key here is engaging the moving glute, and resisting the urge to push too hard into the ground with your palms.
Depending on the "fluidness" of the Smith machine in question, resistance will vary. The goal here is volume: remember, this is accessory work, and, moreover, trying to push too much weight will disengage the glute and force the lower back and abs to fire up. I'll usually follow a drop-set scheme - 30 pounds added to the bar for my first set (10 reps), 25 pounds for 15 reps, and 20 pounds for 20 reps...you get the picture. Whether you start with your lightest weight and more volume or the other way around, perform these donkey kicks toward the end of your training session. You may or may not require assistance walking to the locker room. Gotta love that burn!
Happy butt-building. Enjoy your glutes, enjoy your life!