sentence: There's a young man wearing a blue shirt and black hat demonstrating on a bed and talking about fitness. sentence:  He is talking about fitness as he lays on his back to demonstrate crunches by doing actions with his arms. sentence:  He then shows how to do stomach crunches by holding the back of head with his hands and moving his body back and forth and sideways while folding his knees to his chest. sentence:  He continues doing crunches and then stops.