Even though diet is the most important factor in weight loss the role of exercise cannot be minimized. A few pointers :
To achieve weight loss 450 minutes of exercise a week is necessary. To maintain the weight loss you have achieved at least 300 minutes a week of physical activity is required.
Planks as said in the article are a great way to build core strength. Start with 30 seconds and build up to 180 seconds or more if possible. Side planks are one oft overlooked cor