Erin Pereira, PT, DPT, is a board-certified clinical specialist in orthopedic physical therapy.
Nick Blackmer is a librarian, fact-checker, and researcher with more than 20 years’ experience in consumer-oriented health and wellness content.
Core strengthening exercise programs almost always include some type of lying leg extensions. Depending on the position you’re in, lying leg extension exercises might work your abdominal, pelvic, back, hip and/or knee muscles.
Before deciding whether and how you’ll include lying leg extensions in your back exercise program, it’s a good idea to get the terminology straight.
Technically, leg refers to the lower leg, but many people use this term to refer to the entire lower extremity. When you lie on your back and lift your lower extremity with a straight knee, you’ll be flexing your hip and extending your knee. You could also keep your knee bent; this is usually recommended for beginners who have little abdominal muscle strength and/or those dealing with low back pain.
When you lie on your stomach, you’ll be extending your hip as you bring your lower extremity up towards the ceiling. In this case, you could either keep your knee extended, i.e., straight, or you could bend it, which is called knee flexion. The choice is yours, but each variation will likely make a difference as to which muscles are worked.
Prone (on your stomach) lying leg extensions are a bit more advanced, and best added into an established program.
Regardless of the terminology, prepare for lying leg extensions by positioning yourself with good alignment and engaging your core muscles. As the leg lifts, pelvic and trunk movement will likely result. Your job, or rather the job of your abdominal muscles, is to not let that movement happen; this is how core muscle strength is built.
Core stabilization work such as this targets the transverse, internal and external oblique abdominals the most. But the rectus abdominis muscle, which you may recognize as the “washboard abs” also participates in the movement.
Most people with back pain can get a lot out of a very simple supine (on your back) lower extremity lift. In fact, one or more variations of supine lifts are usually very quickly given to spine patients by their physical therapists.
Many people, whether they realize it or not, use gravity to help get the foot back down to the floor. But working this way tends to have the effect of “skipping” the abs, which won’t do you much good if a strong core is what you’re after. To interrupt this counterproductive exercise habit, consider slowing down the pace at which you bring your lower extremity back to the start position. It’s fine to slow down during the lift phase, too.
Whether you practice this exercise on your back or on your stomach, about 3–10 done with excellent form are all you need. Taking care to maintain a stable trunk position and good alignment as you extend your leg is key to working the muscles that can help your back.
Oliva-Lozano JM, Muyor JM. Core muscle activity during physical fitness exercises: a systematic review. Int J Environ Res Public Health. 2020;17(12):4306. doi:10.3390/ijerph17124306
By Anne Asher, CPT Anne Asher, ACE-certified personal trainer, health coach, and orthopedic exercise specialist, is a back and neck pain expert.
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