Hi welcome to HCm I have gone thru your query regarding sloshy tummy during exercise and how to avoid . sloshy stomach is one of the most common, and problematic, gastric issues in ultrarunning, and recovery takes patience and a willingness to slow down, both of which are usually in short supply during a race . You are right to encourage them to drink before and after the 1 hour of class, if they take lemon juice with water ,a pinch of salt and black pepper and honey , will help resolve their problem . If some need hydration , they can be alowed to take 2-3 small sips during class . It is certainly a derailed life style weakened immunity issue . Accordind to ayurvedic way of treatment all our stomach issues like gastritis , lack of appetite , stomachache sloshy stomach problems are outcome of our disturbed Naval (Nabhi ) known as Suray Kendar , displaced due to over exertion .We face digestive problems as constipatin , dysentary followed by nausea and every other ilness follows . It can be rectified by doing some yoga postures Bhujjangaasan, Dhanuraasan ,Hullaasan , Chakkarasn Pranayam etc . And the importance of balanced diet including all essential nutrients as fiber , vitamins , minerals in natural form ,ginger , garlic , lemon juice with water before meals ,Aloe vera juice + Amla juice 35 ml in the mornlng , coconut water , a spoon of Turmeric powder+ a spoon of Almond oil with a cup of hot milk at bed time all antioxidants , having no side effects , give you instant energy , pave way for your healthy disease free life . It is advised to see your doctor for further guidance Hope this helps solves your query .Take care .All the best .Wish you Good health . Don t hesitate to come back in case of any further query .