I had the same feeling as you at first, and even continued until the next day, when the feeling training part went up. It was during this time that I improved very quickly!
After a lot of anaerobic exercise, blood sugar will drop. In addition to protein, muscle-building powder also contains quite a lot of carbohydrates, which can quickly replenish and restore blood sugar. Adequate blood sugar can better help muscle recovery, and the recovery of blood sugar helps the body to warm up. The combined effect of some factors will make people feel muscle fever or abdominal distension, and different people will feel it in different degrees. In addition, adding taurine to some muscle-building powders can make the body excited and warm. Excluding these factors, part of the reason is that you have an expectation of the fitness effect after using muscle-increasing powder, and you feel that your body is undergoing obvious changes under the psychological effect, which is also a good encouragement to yourself.