A strong backside is about more than just being able to fill out a pair of pants. It's the foundation of strength for the entire body and will allow you to build more muscle all over.
The glutes can handle a tremendous workload, but a lot of the classic big lifts that work the glutes the most – squats, deadlifts, lunges – can take a toll on the lower back and knees in excess. So it's important to sprinkle some more joint-friendly glute exercises into your program to blast your ass without beating yourself up too badly.
RDLs can also be rough on the lower back. If you have a history of back issues or just need something a little more low-back friendly to balance out the other lower back intensive work you're already doing in squatting and deadlifting, do these. They aren't regular trap bar deadlifts (which are more like a squat). Instead, think of it as a regular RDL, just substituting the trap bar for the barbell. You perform the first rep from the floor like a regular trap bar deadlift with some knee flexion, but from there it's a pure hip hinge pattern.
The trap bar lets you keep your hands more in line with your body, thereby reducing shear on the spine. It's very similar to using dumbbells, just with a far greater loading capacity. One cue I like is to think about trying to reach your hands behind you as you lower down. You won't actually be able to do it, especially with heavier loads, but just thinking you will puts you in a better position and allows you to sit back into the hinge more to load your glutes as opposed to your lower back.
The trouble that I've found with bilateral glute bridges is that because it's a relatively short range of motion and you're calling on the strongest muscle in your body (the glutes) to move the load, you can really pile on the weight – far more than you can deadlift. That's not a bad thing alone, but as the loads get heavier, it can get pretty uncomfortable for the neck and hips, and there's a tendency for your body to slide backwards on the floor as you bridge up. And after a hard leg work out, the last thing I feel like doing is loading and unloading a barbell with a shitload of weight. So if I'm being completely honest, I guess it was laziness that drove me to try single leg barbell glute bridges in the first place.
Even though the loads with the single-leg version pale in comparison to what you can handle bilaterally (far less than half), the contraction feels even bigger. Moreover, because the weights are lighter, it's much more comfortable on the neck and hips, and loading the bar isn't nearly as big of an ordeal. As a point of reference, I've done bilateral glute bridges with 585 pounds and have yet to get over 155 on the single-leg version. It can be awkward at first to get the barbell centered on the hips, so I've found it helpful to start the set with a bilateral bridge and then lift one foot once you're already in position, as opposed to starting from the floor on one leg.
You can also start with eccentric single-leg bridges; just bridge up with two legs and lower yourself down with one. The eccentric version is both a great progression to work towards single-leg bridges and a great exercise in its own right if you want to overload the eccentric with heavier loads.
The shoulder and feet elevated hip thrust is a great way to work the glutes and hamstrings through a greater range of motion. It's substantially more difficult than having your feet on the floor though, so don't go trying to add load right away. Your bodyweight should be more than enough to start. Think of it as a controlled thrust. This exercise is better when done in a controlled fashion with a pause at the top of each rep. After you've spent some time mastering the bodyweight version you can add weight by draping chains or weighted vests over your waist. When that's no longer sufficient or practical, try a lightly loaded barbell.
Before you even start, be careful that both benches are secured to the floor so they don't slip mid-set. Then begin by raising yourself up on two legs and getting your bearings before removing one foot from the bench rather than starting on one leg directly from the floor. I also highly recommend resting and resetting between legs to make sure you're situated and stable on the bench before you start.
Here are a few variations of the reverse hyper exercise that are a bit easier on the lower back and don't require any specialized equipment. With a regular reverse hyper, it's easy to descend too far down and go into lumbar flexion at the bottom, which puts tremendous shear on the lumbar spine. Likewise, it's easy to come up too high and hyperextend your lumbar spine at the top, which is also problematic, especially under heavy loads. To avoid this issue, try moving the legs "in and out" instead of "up and down."
Lie prone on a table or bench with your legs hanging off the edge, your knees bent and your hips flexed to approximately 90 degrees. From there, brace your core, squeeze your glutes, and extend your legs straight back behind you. Hold for a brief pause and return to the starting point. When your legs are fully extended, there should be a straight line going from your feet to your head. Since your legs aren't moving up and down in the vertical plane, it's much easier to keep a neutral spine, thereby allowing you to hone in on the glutes without irritating your lower back.
Start with just your own bodyweight until you get the hang of it. Trust me; it's harder than you might think. You should feel it almost entirely in your glutes. If you feel it in your lower back, you're probably raising your feet up too high. Once you can comfortably do a few sets of 8-10 reps with just bodyweight, you can progress by adding ankle weights or putting a small dumbbell between your feet. If you're doing them correctly with controlled form, it won't take much weight at all (around 10-25 pounds tops). You can also modulate the difficulty with your setup position – the more of your torso that's resting on the bench, the easier it will be, and vice versa.
This one is very similar to the modified reverse hypers above, only it's done one leg at a time. I call it "running man" hip extensions because the leg motion vaguely resembles the running stride. Plus, that way it allows me to double-dip and count it as my cardio for the day since it's sort of like running, right? Regardless, the same form cues discussed above all apply. Extend the legs straight back behind to avoid hyperextending the lumbar spine. When one leg is extended completely, the other hip should be flexed at approximately 90 degrees.
The "running man" name is somewhat of a misnomer in that you don't want to fly through your reps quickly. Rather, do them in a controlled fashion with a deliberate pause as you extend each leg, almost like you're running in very slow motion. The unilateral element increases the core and hip stability demands significantly. The key is to avoid motion at the pelvis and lower back and have all the movement originate from the hips. When these become easy, you can either add small ankle weights or progress to the variation below.
These are similar to the running man extensions, only rather than alternating legs each rep, keep one leg fully extended the whole time while the other leg performs all the given reps before switching sides and repeating the process. They don't look like much, but if you do them correctly and do both legs back-to-back with no rest, the burn in your glutes and hamstrings is insane. It's really an advanced exercise so make sure you've got the previous steps down before trying them or chances are you'll be feeling it more in your lower back, which of course we don't want.
None of these reverse hyper variations are meant to replace heavy lifting, but they're great supplemental exercises to give your glutes some extra work without crushing your lower back or knees. They're also great choices if you can't make it to the gym and need something challenging to do at home that doesn't require weights or machines.