Exercise Question: which demonstrator is doing crunchs correctly?

[elfkin477]

Which person in these short video clips is doing abdominal crunchs correctly?

Person A who isn’t bending at the waist enough to touch his knees or person B who is?

Or supposing both are correct ways to do this, is person B benefiting much from exerting herself more than person A?

[CookingWithGas]

Person A is getting full benefit of abs exercise using this form. He is bringing his abs to full contraction.

Person B is contracting the abs, but when she continues to the point of lifting her back off the floor she is then going beyond abs and engaging the upper quads to complete the exercise to the point of touching the knees. This form is “old school” and I’m not surprised it’s from the military (this is how my dad learned to do sit-ups in the Marines) but it’s not harmful.

A variant on Person B that I think is better is to lie down and suspend your feet off the floor, bringing your elbows and knees together. You do lift your back but the tension remains on your abs (whereas Person B gets a chance to relax the abs as she approaches an upright position). Many machines, such as the Nautilus crunch, use that same motion although weight-loaded in an upright position.

Neither one is really right or wrong but exercise different muscles in different ways.

[hksj]

I learned crunches as not fully touching the ground with one’s back between reps. You see how the person in B rests on the ground for a moment and then gives a huge, sudden lurch sufficient to slide her body in order to have momentum on the way up? Ugh…

[Blaster_Master]

@elfkin477

Which person in these short video clips is doing abdominal crunchs correctly?

Person A who isn’t bending at the waist enough to touch his knees or person B who is?

Or supposing both are correct ways to do this, is person B benefiting much from exerting herself more than person A?

Person A is doing what I would call a correct crunch. He’s doing an excellent job maintaining control and not throwing his weight around (i.e., using momentum to complete the repitition). I might say he should go up slightly farther, but its however far you can crunch and ONLY use your abs. The distance will vary based on how tall, strong, and flexible you are, but a rule of thumb is 'til your shoulder blades are off (or just touching) the ground.

As mentioned by CookingWithGas, person B is doing an “old school” version. I’ve generally heard these ones refered to as sit-ups verses crunches. I would generally recommend against this version for two reasons. The first being what was already mentioned, in that you’re not isolating the abs. The second being that it makes it a lot easier to use momentum to complete the repitition. In fact, if you watch the video, the woman doing the sit-ups is actually using momentum.

The main reason for doing the second one is for quantitative judgment of ab strength. That’s why they use them on the physical fitness tests and in the military; its a heck of a lot easier to count and ensure the form is correct for the observer. If you’re just trying to improve ab strength, I’d stick with the form from person A.

[elfkin477]

Thanks for the guidence, but I have follow up questions

1. I’ve been doing crunches (like person A) since posting this thread. Tonight for the hell of it I decided to do the last 50 with my feet up on a low bench, and I felt them a lot more, which is probably a good thing. But why? And it is good, right? It felt more effective…

2. What’s a realistic timeframe for beginning to notice results? (ie a flatter belly) Is New Years too hopeful? With other exercise and diet changes too I’ve lost ~ 3" off my waist since July - yet oddly only about 12 pounds, gaining muscle too maybe - so that’s positive in the meantime anyway.

[Dubious_Weasle]

Yes what person “B” is doing is actually a sit-up. For some reason the Air Force likes calling these crunches. It’s a source of some annoyance as crunches are fine but sit-ups suck for my back.

[daffyduck]

@elfkin477

Thanks for the guidence, but I have follow up questions

1. I’ve been doing crunches (like person A) since posting this thread. Tonight for the hell of it I decided to do the last 50 with my feet up on a low bench, and I felt them a lot more, which is probably a good thing. But why? And it is good, right? It felt more effective…

2. What’s a realistic timeframe for beginning to notice results? (ie a flatter belly) Is New Years too hopeful? With other exercise and diet changes too I’ve lost ~ 3" off my waist since July - yet oddly only about 12 pounds, gaining muscle too maybe - so that’s positive in the meantime anyway.

1. Putting your legs up isolates the abs even more, eliminating the contribution of the hip flexors. That’s why you felt it more. If it feels more effective, it is more effective.

2. There is no hard and fast rule. I’m betting you felt results the first week, right? There is no such thing as spot reducing, and abdominal fat is the last to go and the first to accumulate so losing it is no small task. The number one factor for getting that sixpack look is low bodyfat and not abdominal development. Depending on your body type, you may have to get your bodyfat into single digits.

Another exercise you can try for lower ab development is Reverse Crunches. Notice that he’s using his abs at the top of the movement to lift his rearend up off the bench.

[ultrafilter]

Person A’s exercise seems to be a lot more common, but person B’s is a lot better for her lower back (although it would be better if she were more careful about not bringing her shoulders forward at the bottom). Dr. Stuart McGill, who’s probably the world’s foremost expert in spinal biomechanics, has this to say:

Also among the misperceptions that I hear out there about the rectus abdominis, and upper vs. lower abdominals, is that you’ve got to work the rectus throughout its range of motion. Again these might be muscle physiologists speaking but not people who are cognizant of spinal mechanics. For example, when you look at the architecture of the rectus, it’s a muscle with four heads, four contractile components each separated by a lateral tendon.

If it was a muscle designed to work through its full range of motion it would be one long continuous muscle—but it’s not. It anchors the obliques and transmits the hoop stresses laterally through those lateral tendons. If it wasn’t beaded, the oblique forces would rip it apart laterally. In many elite performances the abdominals contract isometrically. Too many bad backs are created by misinformed people thinking they need to train the rectus with repeated full flexion exercises. There are much better and safer ways to do this.

So again if we’re training athletes to perform, the question is do they need to work the lumbar spine through a full range of motion? Lumbar flexibility often increases the risk of future chronicity!

You can read the full article here, see part 2 here, and read a second interview here.

It’s also worth noting that Dr. McGill specifically denies that it’s possible to isolate your upper or lower abs, or that there are even any such creatures:

T: You’re saying that there’s no way to work the lower-abs vs. the upper-abs, which is very contradictory to conventional wisdom. Can you expand on this?

SM: To be clear, I’m only talking about the rectus abdominus. There have been several problems in the scientific literature leading to misinterpretation. There’s a muscle called pyramidalius, which is a lower muscle that overlays the bottom beads of rectus, but only in some people—it’s an optional muscle.

Those using EMG (electromyography) who claim there is an upper and lower rectus might be monitoring pyramidalius, but if you control with calibrated and normalized EMG our work shows that all four beads of rectus pretty much fire together within the noise and randomness of the signal.

[CookingWithGas]

@elfkin477

What’s a realistic timeframe for beginning to notice results? (ie a flatter belly)

Exercising the abs will not give you a flatter belly. Laying off the pumpkin pie will give you a flatter belly.

Exercising the abs builds those muscles, improving tone and maybe even increasing bulk. A protuding belly is generally due to fat deposits, which you can only get rid of by a combination of diet and general calorie-burning exercise.