The barbell hip bridge is a great exercise to strengthen the hips/legs. The hip bridge, by itself, is a basic movement that works well for beginners. However, once you really learn how to use your hips, you need to challenge the big, powerful hip muscles with some resistance. This is where the barbell comes in. Utilizing a thick foam pad and a heavy-duty roller (or a bench, but I prefer the heavy-duty roller), you can place the barbell on the front of the hips and lift it against gravity. Be sure to keep the spine and neck neutral. It is common for beginners to hyper-extend their lower back and neck when performing this exercise- don't.
Why is this a good exercise to keep in your training tool box?
1. The hip muscles are challenged through the end of the hip extension range of motion (think of sprinting) during the barbell hip bridge. Exercises like deadlifts and squats are most challenging for the hips through the middle part of the range of motion and less challenging closer to full extension.
2. It is a safe and effective exercise for people who don't tolerate deadlifts well. Since the barbell hip bridge loads the spine into spinal extension, it can be used by people who don't tolerate loading into spinal flexion (like a back squat or deadlift). In fact, the barbell hip bridge becomes a good spine "anti-extension"/stabilization exercise when the load on the bar increases.
3. The knees are not stressed as much as with squatting, lunging, or step-ups. If you have knee issues, you may not tolerate going into deep knee flexion very well. During the barbell hip bridge, the knees stay at a fixed angle and don't seem to experience as much stress as squatting or lunging.