What is a hip thrust?

In one line

A hip thrust is an exercise where you lean your upper back on a bench and push a weight resting on your hips upward by straightening your hip joints.

What is a hip thrust?
The exercise where you lean on a bench and push your hips up
At the gym you see people leaning their back on a bench with a barbell across their hips, lifting their hips up. That exercise is the hip thrust. This post explains what the movement is and which muscles it uses.
In a nutshell
Lean your back on a bench and push your hips up
A hip thrust is an exercise where you sit on the floor, lean your upper back on a bench, rest a barbell (a steel bar with disc-shaped weights on both ends) across your hips, and push your hips upward. Your feet stay on the floor and your knees stay bent.
How high?
Until your trunk and thighs are level with the floor
You start with your hips low, close to the floor, and raise them until your trunk and thighs form one line level with the floor. Then you lower and raise them again. In studies, the shins were vertical to the floor at the top.
What lifts the hips?
The force that straightens the hip joint
The hip joint is where the leg attaches to the trunk. As your hips rise in a hip thrust, this joint goes from bent to straight. A study that measured the force at each joint found the hip thrust demanded more force to straighten the hip than the knee, and the ankle did almost no work.
How to measure how hard a muscle works
The electrical signal muscles give off: EMG
Muscles give off a very weak electrical signal when they work. Recording this signal with sensors on the skin is called 'electromyography' (EMG). Studies compare the size of this signal to see how hard a muscle worked.
The main muscle
The gluteus maximus, which forms the buttocks
The gluteus maximus is the large muscle that forms the buttocks; it moves the thigh backward. In women who had been strength training, EMG showed the gluteus maximus worked about twice as hard in the hip thrust as in the squat, the exercise where you sit down and stand back up.
A muscle that helps
The hamstrings at the back of the thigh
The hamstrings, the muscles at the back of the thigh, also work. EMG showed the hamstrings worked harder in the hip thrust than in the squat. They worked less than in the deadlift, where you lift a barbell off the floor and stand up.
A similar exercise: the glute bridge
Shoulders on the floor make it a bridge
Lying on your back on the floor and lifting your hips is called a 'glute bridge'. A hip thrust is a bridge with your shoulders resting on something raised, like a bench, instead of the floor. So the movement starts with your shoulders higher than your feet.
A common misconception
Does the hip thrust grow the glutes more than the squat?
Since the gluteus maximus works harder, it is easy to assume it grows more too. But in studies where people did one of the two exercises for several weeks, the hip thrust did not grow the glutes more. In fact, the front of the thigh grew more in the squat group.
Summary
Straighten the hips to push them up
A hip thrust is an exercise where you lean your upper back on a bench and push the weight on your hips up by straightening your hip joints; it mainly uses the gluteus maximus in the buttocks. Still, in studies lasting several weeks it did not grow the glutes more than the squat. Related terms: squat, EMG, glute bridge.