Exercise that recommended over the years to strengthen your core in daily routine but now time has changed we have to change and gave rest to our body.... As per our modern lives as we planned by latest survey HARVARD UNIVERSITY AND US NAVY are saying that sit-ups and crunches are being replaced by planks which Is effective exercise and is more accurately because it's more effective as it isn't done by a person in position as holding body like arrow as a straight while resting only on toes and the forearms to face effective position not subject muscles to strain by motion ....planks are very effective and they don't strain your back or lower spine and target more muscles groups. And it's essential benefit us that plank is help in mimic in our natural moment whereas sit-ups and crunches force us to into postures you don't want to do everyday.... Push-ups are essential if u r strong enough they help in building more strength....