[Flat-chest dumbbells] mainly exercise the chest muscles. When raising the bar, the bar is directly above the shoulder joint. Push it forward slowly. The wrist joint is not compressed, the elbow joint is not locked, and the shoulder joint is not lifted up. When lowering, the forearm is 90 degrees perpendicular to the ground. The lowering position stops at the chest line. . Keep your shoulder blades retracted and your abdomen tight during the movement, push up for two seconds, come back for four seconds, stay for about half a second when you reach the top, and perform 12 times for three cycles.