Knee-in crunch
Lie face up with your legs outstretched and your hands behind your ears. Lift your legs until they are about six inches above the ground. Engage your core and lift your shoulder blades off the ground. Lift your knees in toward your chest as you do a regular crunch. Don't pull your neck — lift with your abs. Return to the starting position by reversing the movement.
Glute bridge
Put your knees bent and feet flat on the floor as you lie face up. The palms of your hands should be facing down and your arm by your sides. Focus on your head and shoulders. Press through your feet as you inhale. As you exhale, squeeze your glutes to lift your hips off the floor. This exercise can help stabilize your hips and strengthen your abs.
Bicycle crunch
In the face-up position, put your fingertips behind your ears, knees bent 90 degrees, and your feet off the floor. Lift your head and shoulders off the floor. When you extend your right leg straight, bring your right elbow to your left knee. Repeat the movement on the other side, bringing the left elbow to the right knee.
High knees
Standing tall with your feet hip-width apart is the proper posture. Your lower abs should be engaged and your knees should be raised and lowered like you were running. Make sure your knees are the same height as your hips, and your thighs are parallel to the floor. Try to avoid slouching. Keep your weight on the balls of your feet and swiftly alternate your legs.
Push Jacks
As you stand with your feet together, elbows bent, and palms facing up, quickly jump feet apart and pump your arms up toward the ceiling. As soon as you can, reverse the movement and repeat it.
You can perform the core workout suggested above at home without any special equipment. You will certainly achieve a great physique while saving money and time which you were going to pay for the gym.