The problem with leg raises

Posted by Nell Mead at 09:50 on 3 Aug 2011

I went to my usual circuit training session the other day, run by British Military Fitness.  It's a lot of fun: a fairly tough workout with a lot of cameraderie and competition, and outwardly no-nonsense (but actually very humorous) instructors.  They will push you as hard as you want to be pushed, and often very slightly harder.

I love the sessions; but as a punter, you have to remember that most instructors aren't psychic. They will always ask if you have an injury, and will always offer alternative exercises, but they can only help you if you tell them that there is a problem.  This is something that can be tricky unless you are quite confident in your own body and its capabilities (not something I generally struggle with too much, but I've had a lot of practice!).  It's easy to let your competitive side take over, and to start competing in exercises you're not familiar with.  Consequently your form can go to pot as you try to complete that 20th rep before the guy next to you: if you're doing a demanding exercise, that's an easy way to get injured.

One of the exercises I really dislike in that situation is the leg raise, where you lie on your back with your feet together and wave your legs in the air, with an obtuse angle at the hips.  It's an exercise that's supposed to work the lower abdominals and tone the tummy.

The reason I dislike this exercise so much is that the majority of people find it tough to control their torsos in this position.  I have a strong back and good awareness of trunk control, but in this position I find it really hard to stop my low back from arching.  That's because the hip flexor muscle psoas major is being put under a lot of stress to control the momevent of your legs at the hips.  Psoas starts at the sides of your lumbar vertebrae (T12 to L5 to be precise) and goes down to the lesser trochanter of the femur.  When it contracts, these bones are pulled together.

When your back is being correctly stabilised (by, among other muscles, lumbar multifidus and the deep abdominals), the spine is braced to pull your femur forwards and up, so your hip flexes and your legs move up and down.  That's the plan; so far, so good. 

But when your back isn't correctly stabilised - either because of weakness or pain around the low back, or because you're focusing on banging the numbers out rather than on protecting your back properly - your low back can arch and the vertebrae shear forwards towards your hip rather than your hip moving towards your spine in a controlled manner.  I've mentioned forward shear as a bad thing before, when I talked about spondylolisthesis.  So with 80% of the population suffering from back pain at some point during their lives, I'd suggest avoiding this exercise if possible, not because it is intrinsically bad but because many people will do it badly, particularly in a competitive setting.

A good alternative exercise, which will strengthen the deep abdominals safely, is the reverse curl.  Lie on your back with your hips flexed to 90 degrees.  Your knees can be bent or straight, but your hips must not drop below 90 degrees throughout the exercise.  Using your abdominal muscles, pull your legs towards you so that your bottom lifts off the ground.  Hold for a second, then lower it slowly back to the starting position.  If you feel that your back wants to arch as you return to the start, try putting your hands or fists under your bottom (not your back) as this will encourage you to keep your low back in contact with the ground at all times.  This way you will still be working your lower abdominals and your psoas, but there will be no risk of a shearing force damaging your back.

I should mention that after quietly explaining my concerns about this exercise to the excellent BMF instructor, she asked me to show the class and to post about it on the BMF Facebook page.  So Annie, this one's for you!