Swimming is not just about moving forward in the water by using your legs and arms. A strong core is a very importatnt building block for the swimmning technique.
In swimming we use our core muscles mostly for stabilisation. By improving your core strenght you will be able to hold your body straghter, throughout the position and creating less drag and
A strong core gives you a powerful platform from which you can pull, push and kick through the water, ultimately increasing speed. It also gives you a powerful start which you can use for push, kick and pull trough the water and it also helps you to keep your hips high, which reduces drag and makes you more efficient in the water.
Here are some examples for dry land exercises to improve core muscles. They are very simple and you can practise them anywhere.
Lie down on your stomach and stretch your arms straight out above your head (like Superman flying). Flex your glutes and tighten your stomach, then lift your right arm and left leg. Then do the other arms and leg.
Lie down on the floor with your palms under your hips.Put your hand under your buttKeeping your abs tight, alternate between your right and your left leg, lifting each 45 degrees in the air and lowering to their starting position.Continue kicking your legs up in the air
Rest your forearms on the floor, with your elbows directly underneath your shoulders and hands facing forward so that your arms are parallel.end your legs out behind you and rest your toes on the floor. Your body should form one straight line from your shoulders to your heels.Make sure you are not dropping your hips or hiking your butt up high toward the ceiling.
Lie down on your back, keep your knees bent and feet flat on tha mat. Lift up your torso and sit up. Return to the startinh position by rolling down. If you want to make it more as a challange then pull up your legs in 90 degrees.