Mid or low back pain, abdominal injury / surgery and / or excessive lengthening due to pregnancy can cause a delay or absence in the anticipatory contraction of transversus abdominis. (dianelee.ca)
At a deeper level, you have the deep transversus abdominis muscle layer, the layer we often ignore when we train. (cathe.com)
Now I will preface this by saying that this specific exercise does NOT increase fat burning, but it CAN help to flatten your stomach by strengthening your deeper transversus abdominis muscles and hence «pulling in» a lazy stomach (aka beer belly or «pooch belly»). (truthaboutabs.com)