The deadlift is a very popular exercise used mainly by powerlifters but also by athletes and fitness buffs. Because many strength and conditioning coaches use powerlifting as the format for training the athletes, the deadlift becomes an especially important exercise. The deadlift is used as the exercise to strengthen the hamstrings and gluteus maximus muscles.
How effective the deadlift is in strengthening these muscles depends to a great extent on how the exercise is executed, especially in regard to range of motion in the hip joint. To effectively target these muscles there must be a maximum range of motion in the hip joint which means that the trunk should get level to the ground and the legs should be straight. This is why the straight leg deadlift is best for development of these muscles.
However, the straight leg deadlift is usually too difficult to execute. As a result, most athletes do a combination squat/deadlift. This means that they usually do about a quarter squat together with the raising of the trunk. But, because of the bent knees, the hamstrings are not taut which is not conducive to their getting strengthened. In addition, the spine must be kept in an arched position. If the back is slightly rounded it gives more slack to the hamstrings further decreasing the effectiveness of the exercise.
Many coaches also consider the dead lift exercise an effective lower back strengthening exercise. However, strengthening the lower back muscles is not the prime purpose of this exercise, even if it does strengthen the lower back muscles in the isometric regime. The isometric strength helps to develop stabilization strength of the lower back muscles which are responsible for holding the normal position of the spine. In the deadlift the lower back muscles must stabilize and hold an arched position of the spine throughout the execution.
In this respect, greater back strength is an important by-product of doing the deadlift. However, the only exercise that fully strengthens the lower back muscles is the back raise which is most effectively done on the Yessis Glute Ham Back Machine, especially if you are very tall or short. Doing hip extension exercises on this machine is also great for strengthening the hamstrings and gluteus maximus and developing greater isometric strength of the lower back muscles.
Thus although you get greater back strength when you do the deadlift, it is not the best exercise for strengthening the lower back muscles. But rather than doing more effective exercises, some coaches still use the deadlift for back strengthening. To get greater back strength they have the athlete round the back in the down position and then arch the back as they come up to the erect position.
However, rounding the lower back, especially when handling relatively heavy weights, can be injurious to the lower back. In fact, this is one of the main reasons why back injuries occur. When the athlete has a rounded back when handling heavy weights overhead or on extended arms in front of the body, the stress and pressure on the discs in the lumbar area are extremely high. If the muscles are not strong enough to withstand the forces that are developed, an injury can easily occur.