Classic Floor Sit-Up (Curl-Up) Exercise Guide
The classic floor sit-up is still used in many training programs. It can be a good abdominal exercise (under certain conditions) but should definitely be avoided if you have any lower back problems or have a weak core.
Sit-ups and crunches are sometimes used interchangeably, but there are some noticeable differences between these two exercises. Sit-ups are generally a larger movement compared to crunches because you are raising your torso until you reach a semi-seated position. A similar move, the crunch, involves lifting only your head and shoulders (upper back) off the floor to move your ribcage toward your pelvis, without lifting your lower back.
With any sit-up-type movement, your abdominals are involved only in the first part of the motion. After your shoulders clear the floor, your hip flexor and lower back muscles take over. So there’s no point in sitting all the way up to your knees. Raise your torso no more than 30-40 degrees.
How to Perform the Classic Floor Sit-Ups?
To perform the classic floor sit-ups first lie on your back with your feet flat on the floor and knees bent about 60-90 degrees. Place your hands behind your head (fingers interlocking). As alternative, you can cross your arms across your chest. Where you place your hands determines the difficulty of the crunch. The exercise is harder when your hands are behind your head, easier with your hands crossed on your chest. You can also place your finger tips behind your ears or you can extend your arms straight out in front of you as you curl up. Place your feet under a support (not shown on the image) – such as a barbell, or the base of a weight machine, for example. This will help you to stabilize your lower body. Your heels should be about 12 to 18 inches from your buttocks.
Engage your core muscles and slowly raise your torso upwards at a constant speed (without jerking or accelerating), leaving just your buttocks and feet on the floor. Raise your torso until you reach a semi-seated position (30-40 degrees). Pause at the almost upright position, then slowly lower your upper body until it is almost parallel to the floor. Don’t come down all the way. Don’t bring your torso so far forward that your elbows touch your knees, for the same reason that you don’t lower yourself all the way: both can cause back pain or injury. Do not pull on your neck.
When performing the classic floor sit-ups try to maintain proper lumbar posture throughout the movement by bending at the hips and upper back and limiting the range of motion in the low back. You can hook the feet under something heavy to allow more torque production at the hips. Perform the movement under control and accentuate the negative portion (lowering component) of the exercise rather than cranking out 100 repetitions in a ballistic manner.
The classic floor sit-up (or any sit-up variation) targets your rectus abdominis (especially upper part), but a number of other muscles are also involved, from your abdomen all the way down to your ankles. The assisting muscles — iliopsoas, tensor fasciae latae, rectus femoris, sartorius, obliques — are essential to get you through a sit-up motion. As you go through the upward motion of a sit-up, you may feel slight tension through the front of your legs. This is your tibialis anterior engaging. While the sit-up does not strengthen this muscle, it does use it to keep your ankle stabilized.
Those exercise variations are much better choice that the classic floor sit-up.
(1) Abdominal Bench Sit-Ups. Resting your legs on a flat exercise bench or other elevated platform isolates your abdominals from the assistance of your hip flexors during the sit-up exercise, providing a more intense abdominal workout.
(2) Roman Chair Sit-Ups. A Roman chair has a seat that’s about knee high (with no back) and a low horizontal bar near the floor in front of the seat. Sit upright with your legs bent toward the floor. Extend your legs slightly and place your feet under the support, pressing them up against it. Fold your arms across your chest in an X. Lean your torso back until it’s almost parallel to the floor—this is the start of the movement. Now raise your torso several inches toward your knees (but well short of upright) until your abs no longer flex. Pause, then lower yourself to the starting position before raising your torso again.
It’s ironic, but the sit-up, which is the most popular exercise in the world for the abdominals, might be the absolute worst exercise and could even be dangerous for some people under some circumstances. During a sit-up, your main trunk flexor, the iliopsoas muscle, often does the majority of the work while the abs are not optimally recruited. Because the iliopsoas muscle originates on the lower back, the sit-up literally pulls on the lower back with every repetition, especially if your feet are held down or anchored, or the repetitions are performed quickly in a jerky fashion. This is why too many sit-ups can lead to a strength imbalance between the iliopsoas and abdominals, as well as poor posture and lower back pain. So for bodybuilders, we recommend crunches over sit-ups. If you decide to perform this exercise than you should rest your legs on a flat exercise bench or other elevated platform to isolate your abdominals from the assistance of your hip flexors during the sit-up exercise.