With your feet hip-width apart, stand holding a barbell on the back of your shoulders, grasping the barbell at each side.
Keeping your back neutral, inhale as you flex your hips and, slightly, your knees to lower your torso until it is close to, or fully, parallel with the floor.
Exhale as you raise your torso back to starting position by extending your hips and knees.
Repeat until you meet the desired number of repetitions.
Comments and tips
For your safety, do not flex your hips beyond feeling a mild stretch in your hamstrings. Depending on the flexibility of your hamstrings, you may need to flex your knees more in order to lower your torso to the desired level.
Maintain a neutral back and neck when performing this exercise. Do not keep looking forward when lowering your torso.
Start with a light weight and add more weight gradually. This will allow your lower back time to adapt.
The barbell bent-knee good morning is a hip-hinge exercise since it primarily utilizes hip extension. Even though there is movement in the knees, it is also classified as an isolation exercise because the movement in the knees is (or should be) minimal.
The two main muscle groups that are involved in hip extension are the gluteus maximus and hamstrings. In the barbell bent-knee good morning, the gluteus maximus is emphasized over the hamstrings. This is because, as the knees flex, the hamstrings become loose, which forces the gluteus maximus to contribute more to the movement. On the other hand, if the knees were kept extended or very slightly flexed, such as with the barbell good morning, the hamstrings would be emphasized over the gluteus maximus.