I like Yuri’s answer here abouat situps so I’ve copied his full post below:
Yuri Elkaim, BPHE, CK, RHN, is a registered holistic nutritionist, fitness expert and highly sought-after high-performance health coach. He’s also a former professional soccer player and served as the head strength and conditioning and nutrition coach for men’s soccer at the University of Toronto for seven seasons. For more than 13 years, he’s empowered more than 86,000 people to greater health with his no-nonsense approach to health, fitness and nutrition. He’s made it his mission to empower at least 10 million people to greater health and fitness by 2018. Get Yuri’s free “Y-Factor” at www.yurielkaim.com.
I am often asked if doing situps or crunches will get people the toned six-pack abs they’re looking for. Unfortunately, even if you do 100 crunches a day, you won’t lose the fat from your belly. Not a chance.
The only way you can lose fat from your belly is to lose fat from your entire body. Situps and crunches simply won’t do this for you, even though I’m sure you’ve heard otherwise. What is important to understand is that there’s a big difference between strengthening your ab muscles and losing the layer of fat on top of them.
At the end of the day, when people say they want a six-pack or a flat belly, what they really mean is they want to get rid of the layer of fat covering the muscles in their midsection. You can think of doing situps and crunches kind of like doing a bicep curl. Each type of exercise strengthens a specific group of muscles. And because both muscle groups are small, working them will not cause you to burn fat.
In order to lose fat, your body temperature must increase enough to trigger the metabolic effects necessary to burn fat. Using one small muscle group, such as the abdominals or the biceps, is not significant enough to create the amount of heat necessary for fat burning to begin.
You can think about it like this: If the muscle group is small, the amount of heat it creates will also be small. To give you a better idea of how this process works, pretend the layer of fat you want to lose from your body is like wearing a jacket. If you were to do bicep curls or crunches, you probably wouldn’t generate enough heat to make you want to remove the jacket.
Now imagine you perform full-body exercises such as running up hills, stairs or circuit training with the same jacket on. I think it’s safe to say that after just a few minutes, you’ll want to rip that jacket (layer of fat) off. The reason the second type of exercise generates so much more heat than bicep curls or crunches is simply because they are high-intensity activities that use multiple muscle groups.
This is why high-intensity, full-body exercises are more effective for fat loss than situps or crunches. The bottom line is that spot reduction is a myth, so you can save your money on all those gadgets, gizmos and workout plans being advertised. They don’t work. In order to have a flat belly, you have to reduce your total body fat percentage — and situps simply can’t do this.
High Intensity = High Heat
As I mentioned above, running hills is a great example of an exercise that uses both the upper and lower body. This high-intensity exercise generates a tremendous amount of heat in the body, which you now know is essential for fat loss.
If you can, think back and compare the amount of heat you would feel doing situps, and then compare it to the amount of heat you would feel after running up and down hills. The difference is extraordinary.
Just to be clear, I’m not saying you have to go out and run hills in order to have a flat belly and toned abs. Any exercise that gets multiple muscle groups involved is high intensity, and it will increase your body temperature and get your fat burning.
Better yet, if you combine two resistance-training exercises, such as bicep curls and lunges, followed by squats and shoulder presses, you’ll not only create a ton of heat in the body — you’ll also be building muscle mass.
Building muscle is what gives your body the toned shapely appearance everyone is after. Another positive that comes with building muscle mass is the fact that it increases your metabolism. Think about it like this: The more muscle mass you have, the hotter your fat-burning engine will burn during your exercise sessions. And that is exactly what you want if having a flat belly is your goal.