Side planks engage the muscles of the core, most noticeably the internal and external obliques. This is very different from heavy lifting which can over load the obliques and cause a thicker looking waist thus losing the feminine hourglass shape. With side planks the aim is to strengthen and streamline your obliques with creating a blocky muscley look.
The plank is probably the most popular and effective core exercise, despite this most people do them incorrectly. To really engage the core make sure you squeeze your glutes and keep your body straight while conducting the exercise. Try and pull your lower abs up to your spine which will create a posterior tilt to your hips and this will ensure you are in the correct position. Try not to say your hips as this will cause you to lose the activation of the core muscles.
Swiss ball roll outs
A progression of the plank is the Swiss ball roll out, I can make this more or less challenging by either doing it from your knees or your feet. Rest your elbows on the ball and assume the plank position, slowly roll the ball away from yourself remembering to engage the core as previously stated in the plank exercise. Hold for 2 seconds then repeat backward s and forwards in a seesaw motion, this is a very effective exercise for core stability due to the amount of stress that it applies to the abs, oblique’s and lower back.
Jumping oblique twists
This is a great cardio move to help burn calories, minimize belly fat and tone the sides. Oblique moves like this one create muscles that pull your body inwards, creating the look that you're after.
The Russian Twist
Twisting whilst keeping your abs stabilized in a strong position is what makes this exercise so effective at tightening your waist, it works the whole abdominal region including the transverse abdominals which lay beneath the outer abdominals. Try slowing the exercise right down to make it more challenging.
If you girls out there are strength training and want to maintain that small waist, it’s a good idea to think about wearing a waist trainer, especially if you’re squatting and deadlifting a lot (which you should be). These will keep your waist sucked in during the exercises that may cause it grow and look blocky.
Everyday habits that will help you achieve your goal:
Do 30-60 minutes of cardio at least 5 days a week - Regular cardio will keep your heart healthy, and make it easier to maintain a healthy bodyweight, which is absolutely essential to having abs or a thin midsection. Also, if you focus only on working out or doing situps and don't make the necessary modifications to your diet, you will likely never see the results of all of your hard work show up in the form of a toned belly.