Lying face down on the ground, prop yourself up into a forearm plank position. Make sure your elbows are aligned underneath your shoulders, and that your hands are balled up in fists.
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Dead bug
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Lay face up on the floor with arms straight above your shoulders. To start, bring your knees directly over your hips and bend at the knee so that your calf forms a 90-degree angle with your thigh
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Hollow extension-to-cannonball
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Get into a cannonball-type shape on your back, hugging your knees into your chest—yes, just like you’re at the pool at summer camp again. Simultaneously extend your legs and arms outwards into a “hollow” position, pressing your lower back to the floor.
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Dumbbell side bend
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Stand with your feet hip-width apart and hold a dumbbell in your right hand, palm facing inwards towards the torso. Keep your back straight, activate your core, and then bend to the side as far as possible—but only at the waist
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Barbell back squat
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With your feet shoulder-width apart, lift a barbell off the rig, centering it evenly across your shoulders. (This version of the squat targets the core, not the legs, and so you should be using far less weight than you would for a traditional back squat.)