A 5 kg plate on your chest is probably not enough. The measurement gives the threshold.
Weighted crunches answer a real problem: at bodyweight, the abs finish a set of 30 repetitions without ever working near their maximum.
Adding load solves that, as long as the jump is big enough. Moraes et al. (2009) measured the point where activation starts to change.
The measured threshold: 20% of 1RM
Moraes et al. (2009) had 13 trained participants perform crunches at four loads drawn at random: 20, 40, 60 and 80% of their one-repetition maximum. Five minutes of rest between sets. Surface electrodes recorded the rectus abdominis, the external oblique and the rectus femoris.
Neighbouring loads produced no different activation. Going from 20 to 40% of 1RM changes nothing measurable. The authors conclude that to progress in abdominal strength, the increase must exceed 20% of 1RM.
If your weighted crunch set tops out around 20 kg, the next step sits above 24 kg, not at 22. On a stack with 5 kg plates, that is one full plate. On a disc held against the chest, it is the move from 20 to 25 kg.
Where you place the load changes which part works
Gomirato and Grenier (2023) used M-mode ultrasound on the four segments of the rectus abdominis in 15 participants, during a 45° crunch, a 90° sit-up and a 90° leg raise.
Mean thickening of the rectus abdominis was 36.4% greater during the crunch than during the leg raise, and 32.5% greater during the sit-up. All three exercises shorten and thicken the muscle, but the crunch does it most clearly.
Their most useful observation is about distribution: recruitment concentrates on the segment closest to the load. A plate held behind the head and a cable pulled above the shoulders do not load the same storey of the muscle.
The machine does not replace the load
Nelson et al. (2012) compared the traditional crunch to the basic jackknife on the Ab Lounge, a device sold as an equivalent, in 22 subjects. EMG activity of the upper rectus abdominis was higher with the traditional crunch (F = 4.39, p = 0.04). On the lower rectus abdominis the crunch also led, without reaching significance (p = 0.62).
The floor crunch holds up against the dedicated device. What the crunch lacks is not a mechanism, it is an adjustable load.
What load will not do: reveal your abs
Vispute et al. (2011) split 24 sedentary adults into two groups. The training group performed 7 abdominal exercises, 2 sets of 10 repetitions, 5 days a week for 6 weeks, on a constant calorie intake.
No significant effect on body weight, body fat percentage, android fat, abdominal circumference, or the abdominal and suprailiac skinfolds. Abdominal endurance did improve: 47 ± 13 curl-up repetitions against 32 ± 9 for the control group.
Loading the crunch is a hypertrophy and strength decision, never a definition one. How visible the rectus abdominis is depends on the fat layer over it, which those 6 weeks did not move.
Load is worth it if
Your ab sets run past 20 repetitions, you want thickness on the rectus abdominis, and you can progress in steps of at least 20%.
Load adds nothing if
Your goal is waist circumference, or if you add 2 kg per session. Under the threshold from Moraes et al., that is the same set with a plate on top.
The 24 crunches in the Overload exercise reference
The Overload exercise reference holds 897 movements, 98 of which have the abdominals as their primary muscle, 24 of which carry the crunch name. Nine of those 24 work against an external load, on a cable, a machine or a plate. The other fifteen are bodyweight.
Members do not spread their sets evenly across them. The nine loaded variants take 580 of the 812 logged uses, or 71%, and the top two places in the ranking.
| Variant | Load | Member uses |
|---|---|---|
| Cable Crunch | Cable | 349 |
| Ab Crunch Machine | Machine | 161 |
| Crunches | Bodyweight | 133 |
| Oblique Crunches | Bodyweight | 67 |
| Weighted Crunches | Plate or dumbbell | 42 |
| Kneeling Cable Crunch With Alternating Oblique Twists | Cable | 17 |
| Cross-Body Crunch | Bodyweight | 15 |
| Cable Seated Crunch | Cable | 9 |
One point on method: this counter adds up how often the movement appears in sessions members logged, not sets and not individual people. A variant placed well in the app's search starts with an advantage.
The ranking still says something on one point. The bodyweight crunch, the exercise everyone knows, lands third behind two variants you adjust in kilos. The cable is the format members pick when they decide to load, which the cable training guide explains through its constant tension across the range.
Practical recommendations
- Find a load that brings you to failure between 8 and 15 repetitions first. Under 20 bodyweight repetitions, there is nothing yet for load to fix.
- Progress in steps above 20% of your current load, per Moraes et al. Write the load down, or the step stays invisible.
- On a cable, keep the hips fixed and flex the spine. A cable crunch that turns into an arm pull loads the lats, not the rectus abdominis.
- Place the load according to the segment you want, since recruitment follows the load in Gomirato and Grenier: behind the head for the upper rectus abdominis, on a low pulley in a reverse crunch for the lower part.
- Do not count on these sets for your waist. Six weeks of daily ab work changed nothing in the skinfolds in Vispute et al.
A 20% step shows up in the numbersOverload is a structured strength-training app. Every set you log carries its repetitions and its load, and the Analysis tab keeps a list of estimated 1RMs per exercise, with a progression chart and a confidence tier. A cable crunch becomes a numbered set you can compare from session to session, which a set of floor crunches does not allow. Get Overload and log your current crunch load, so you know which kilo your next step sits at.
Conclusion
Loading the crunch works, as long as you move in steps of at least 20% of your maximum, which a hand-held plate does badly and a cable does well. Overload members settled this before the study did: 71% of the crunches they log are loaded. And none of those sets will reveal your abs, that work happens at the table.
- Moraes AC, Pinto RS, Valamatos MJ, Pezarat-Correia PL, Okano AH, Santos PM, Cabri JM (2009) — EMG activation of abdominal muscles in the crunch exercise performed with different external loads. Phys Ther Sport, 10(2), 57-62.
- Gomirato AP, Grenier SG (2023) — Diagnostic ultrasound shows preferential activation of rectus abdominis segments with exercises targeting upper versus lower segments. Int J Exerc Sci, 16(1), 1077-1086.
- Vispute SS, Smith JD, LeCheminant JD, Hurley KS (2011) — The effect of abdominal exercise on abdominal fat. J Strength Cond Res, 25(9), 2559-2564.
- Nelson GA, Bent-Forsythe DA, Roopchand-Martin SC (2012) — Electromyographic activity of the rectus abdominis during a traditional crunch and the basic jackknife exercise with the Ab Lounge. J Strength Cond Res, 26(6), 1584-1588.
This article presents the current scientific evidence. For a personalised program, consult a health professional.