Sit-ups once ruled as the way to get tighter abs and a slimmer waistline, while “planks” were simply some kind of flooring. Now planks, an isometric core strength exercise that involves maintaining a position similar to a push-up for the maximum possible time, are the gold standard for working your core, while classic sit-ups and crunches have fallen out of favor. Why the shift?
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One reason is that sit-ups are hard on your back — they push your curved spine against the floor. Sit-ups also work your hip flexors, the muscles that run from the thighs to the lumbar vertebrae in the lower back. When hip flexors are too strong or too tight, they tug on the lower spine which can be a source of lower back discomfort.
Second, planks recruit a better balance of muscles on the front, sides, and back of the body during exercise than sit-ups, which target just a few muscles. Remember, your core goes far beyond your abdominal muscles.
It doesn't matter where the motion starts, it goes up and down throughout the body. Weak or inflexible core muscles can impair how well your arms and legs function, as well as everything else. In doing so, it takes power from many of the moves you make. Properly building up your core increases the power. A strong core also enhances balance and stability helping prevent falls and injuries.
What most people don't realize, a strong core supports everything we do. Whether you're playing golf or tennis, to bending over putting on your shoes or picking something up off the floor, to even sitting at your desk for long periods of time.
All of these activities of daily living, call on your muscles to work together, not in isolation. Sit-ups or crunches strengthen just a few muscle groups. Yes, I'm sure some may want rock hard abs, the six pack, and that's OK if you do. But only focusing on that one muscle group, and not focusing on your overall strength, including your back and flexibility with exercises like yoga, will help you live a more safe and balanced life.