reckonerCrunch
The plain floor crunch: lie down, curl your shoulders toward your hips, come back down. It is small, it needs no kit, and measured against a row of ab machines it was among the best for the abs1. What it asks for is a curl of the spine, not a pull on the head.
Curl the ribs toward the hips.
- Pattern
- Core flexion
- Trains
- Abs
- Kit
- Bodyweight, floor
- Loading
- Your own bodyweight
- Reckoner prescribes
- 2 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
Lie down with knees bent
Back on the floor, knees bent, feet flat about hip width apart. Bent knees keep the hips out of the way so the abs do the curling. Hands rest lightly beside your head or crossed on your chest.
Curl the ribs toward the hips
Lift your head and shoulder blades off the floor by rounding your upper back. The lower back stays on the floor the whole time, because a crunch is the spine curling, not the hips folding.
Pause at the top
Stop where your shoulder blades are clear of the floor and hold for a moment. The pause takes the bounce out and makes the abs hold the curl. Going further turns it into a sit-up.
Lower slowly
Uncurl back down under control until your shoulders touch the floor. The way down is half the rep, so give it the same time as the way up. Reset, breathe, and go again.
What goes wrong
Pulling on your head
Pulling on the head makes the top of the rep come easily, so it feels like a good set. The neck moves and the abs barely do. Let the hands rest. If you need to pull, the set is done.
Sitting all the way up
More range looks like more work. Past the point where your shoulder blades clear the floor, the hips start doing the lifting: the bent-knee sit-up drew more hip flexor activity than the crunch did1. Stop at the curl.
Dropping back down
Dropping lets you start the next rep sooner, so high counts come easily. Rushing the way down halves each rep. Lower as slowly as you came up.
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 | 2 x 10 | More reps 10 → 11 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 2 | 2 x 11 | More reps 11 → 12 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 3 | 2 x 12 | More reps 12 → 13 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 4 | 2 x 13 | More reps 13 → 14 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. |
| 5 | 2 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 | 1 x 14 | More reps 14 → 15 repsYou finished every set with three reps left in the tank (RPE 7) and room left in the range, so the reps climb before the load does. The lighter week is over, so this is back to two 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
Will crunches flatten my stomach?
No, and no ab exercise will. Six weeks of ab training in sedentary adults, with food held level, improved ab endurance and left body fat, waist size and skinfolds where they were2.
Are crunches worth doing at all?
Yes, for the abs. The crunch was among the highest exercises measured for upper and lower rectus abdominis and both obliques, level with machines built for the job1. When it gets easy, the cable crunch is the same movement with load.
Will Reckoner put this in my plan?
It can, as an ab exercise that needs nothing but a floor. Lower back is recorded against it, as it is against every crunch, so declaring it in setup takes it out of your plan.
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
- 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 seven commercial ab machines, the crunch and the bent knee sit up, with the crunch among the greatest for upper and lower rectus abdominis and both obliques. Twenty years old, and the same source the cable crunch page cites
- Vispute and colleagues, Journal of Strength and Conditioning Research, 2011. The effect of abdominal exercise on abdominal fat twenty-four sedentary adults randomized to six weeks of abdominal training or nothing on an isocaloric diet, with no significant effect on body weight, body fat, android fat, abdominal circumference or skinfolds, and a significant gain in curl up endurance. Over five years old, and still the trial that measured it