The typical gym member might do a few sets of back extensions at the beginning of a workout, as a warm-up, or at the end of a workout if they finished early. Seldom is more than bodyweight used in these exercises, and usually 10-15 reps are performed. It’s better than nothing, but back extensions offer a lot of benefits for both athletic and physical fitness improvement if they are taken seriously.
One of the muscle groups back extensions target is the erector spinae, which contain three parallel sets of muscles (iliocostalis, longissimus and spinalis). These muscles run the down spine from the base of the neck to the sacrum. These muscles help you maintain optimal posture of the spine when lifting, and are involved in extending and laterally flexing the vertebral column. Other muscle groups involved in back extensions include the hamstrings (although not for knee flexion), gluteus maximus, and the adductor magnus.
The sequence that the muscles are activated in both of these variations of back extensions is as follows: calves, hamstrings, glutes, and erector spinae. As a bonus, at the beginning of these movements the exercises provide traction on the spine, which is why they are a popular exercise to perform at the end of a workout involving heavy squats or deadlifts.
Training the erector spinae produces an “irradiation effect,” which means that if you strengthen these muscles it will increase the strength of many other muscle groups. As such, if you strengthen your lower back, you might experience an increase in the weights you can use for squats and even overhead presses.
Many weightlifters and powerlifters find that performing a few light sets of back extensions helps prepare them for their primary lifts. Ken Clark is a US weightlifter who competed in the 1984 Olympic Games and officially clean and jerked 469.5 pounds while competing in the 220-pound bodyweight class. Clark would start his workouts with several sets of bodyweight back extensions before every training session. In contrast, many Russian weightlifters in the 70s would train back extensions hard and heavy, often with several hundred pounds resting across their shoulders.
Back extensions tend to emphasize the mid-portion of the spine (above L3), which is in contrast to the reverse hyper that emphasizes the lower part of the lumbar spine (below L3). Thus, for structural balance, both exercises should be planned into long-term program design.
The most popular types of back extension units are the horizontal back extension bench and the 45-degree back extension bench. Both place minimal compressive forces on the spine, but the 45-degree unit permits a greater range of motion. Also, with the 45-degree bench, the stress with greater at the start of the movement, whereas the highest level of stress in a horizontal back extension is at the top of the movement.
For those with a history of lower back pain, the 45-degree back extension may be a better exercise because it’s easier to feel if you are going into hyperextension, which may cause discomfort or even back spasm. The downside is that with a greater range of motion, there is often a tendency to round your back with the 45-degree unit.
Regarding seated back extension machines, Swedish sports scientist Alf Nachemson published a study in 1975 that showed that leaning forward approximately 15 degrees from a seated position may double the compressive forces on the L2-3 vertebrae. As such, those with a history of back problems should probably avoid this variation.
One of the mistakes many individuals make is only performing back extensions for high reps, thus reducing the intensity of the exercise. The issue is that the erector spinae contains both fast-twitch and slow-twitch muscle fibers, so one set/rep prescription will not produce complete development of these muscles. As such, you should perform these exercises with heavy weights for low reps and with relatively lighter weights for high reps. For example, you might perform 3-5 sets of 3-5 reps for several weeks followed by 2-3 sets of 10-15 reps for several weeks.
To increase resistance, lifters often perform the back extension by holding a weight plate across their chest or a barbell across their shoulders. Another option is to place a straight bar in front of you with the bar directly over your shoulders, grasp the bar with an overhand grip, and extend your spine. Because weight plates reduce the range of motion, you should use a wider grip or place smaller-diameter weight plates on the bar. Using lifting chains and bands can also make these exercises more challenging and provide variety in how the muscles are stressed.
If you want to become a better athlete, an overall stronger athlete, or just enjoy a better quality of life with a healthy spine, consider adding back extensions to your training toolbox.