reckonerSit-up
The sit-up is the oldest abdominal exercise there is and the one with the most argued-about reputation. It trains the abs, it also asks a great deal of the hip flexors, and the case against it is more interesting than either side usually admits.
Curl up slowly, don't yank the neck.
- Pattern
- Core flexion
- Trains
- Abs, hip flexors
- Kit
- Bodyweight, floor
- Loading
- Your own bodyweight
- Reckoner prescribes
- 3 sets of 10 to 15 reps at RPE 8
- Progression step
- Nothing to add, so the sets climb instead
- Skill
- Simple to learn
- Recovery cost
- Very low
- Not prescribed if you have declared
- Lower back
Muscles worked
How to do it
Set the feet and the knees
On your back, knees bent, feet flat and a comfortable distance from your backside. Anchoring the feet under something makes the exercise easier by letting the hip flexors pull harder, which is worth knowing before you decide to do it.
Curl before you hinge
Start by rounding the top of your spine and lifting the shoulder blades, so the abs do the first part. Only then let the hips fold to bring you upright.
Keep the hands off the neck
Arms across the chest or fingertips lightly at the temples. If your hands are laced behind your head you will pull, and the neck will be what hurts tomorrow.
Lower with the same shape
Go back down slowly, reversing the fold and then the curl, and touch the shoulder blades to the floor before the next rep. Reps that drop and bounce are reps you did not do.
What goes wrong
Hauling on the back of your head
The set gets hard, the hands take over, and the chin drives into the chest. It buys reps and it loads the neck. If your hands are helping, the set was already finished.
Hinging from the first inch
Coming up as a straight plank from the hips is a hip flexor exercise with a spectator abdominal wall. The curl at the start is what makes it an abdominal movement.
Bouncing off the floor
Speed and a bit of rebound turn twenty into forty. The abdominal work is in the slow curl and the slow return, and both are what the bounce removes.
How Reckoner progresses this lift
Six weeks of this lift, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 3 x 10 | More reps 10 → 11 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 2 | 3 x 11 | More reps 11 → 12 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 3 | 3 x 12 | More reps 12 → 13 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 4 | 3 x 13 | More reps 13 → 14 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 5 | 3 x 14 | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 2 x 14 | More reps 14 → 15 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. The lighter week is over, so this is back to three sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Are sit-ups bad for your back?
Here is the honest version. Repeated flexion and extension under modest compression reliably produced disc herniation in isolated pig spine segments in a testing rig1, and the bent-knee sit-up has been measured producing the highest hip flexor activity of the abdominal exercises in its group, which the authors flag as a possible problem for people with low back pathology2. What nobody has shown is a trial in living people finding that sit-ups cause back injury, and that gap belongs in the answer rather than out of it. If your back is fine, sit-ups are a legitimate exercise. If it is not, there are exercises in this library that ask less of it.
Why do my hip flexors do most of the work?
Because past the first part of the movement they are what brings you upright, and anchoring your feet lets them pull harder still. That is the design of the exercise rather than a fault in how you are doing it.
What should I do instead if I want the same thing?
A crunch keeps the abdominal work and drops most of the hip flexion, and it measures at least as well for the rectus abdominis and the obliques2. Reckoner has both, treats them as alternatives, and will give you one in place of the other.
Similar movements
There is no load to ease on this lift, so Reckoner offers one of these the first time it stalls. Each of them has a page.
Sources
- Callaghan and McGill, Clinical Biomechanics, 2001. Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force isolated pig spine segments in a testing rig, up to 86400 bending cycles, where herniation occurred under modest compression but highly repetitive flexion and extension, which is a finding about young non-degenerated tissue in a machine rather than about a person doing a set
- Escamilla and colleagues, Journal of Orthopaedic and Sports Physical Therapy, 2006. An electromyographic analysis of commercial and common abdominal exercises: implications for rehabilitation and training fourteen participants across nine abdominal exercises, with the crunch among the highest for upper and lower rectus abdominis and for both obliques, and with rectus femoris activity greatest in the bent-knee sit-up, which the authors say may be a problem for people with low back pathology