When you say "red" when practicing chest muscles, you actually mean that the muscles are congested, the body temperature rises during training, and the blood flow speed is accelerated. In addition, muscle movement and the "external" pressure of the cardiovascular system force blood to flow to a specific training muscle area, while there is no corresponding "internal" pressure inside the muscle to discharge blood, so excess blood will stay in the muscle for a period of time, which will lead to muscle expansion and congestion. However, with the end of training, the body temperature drops, the blood flow rate decreases, the cardiovascular system and muscle activity slow down, and the blood will gradually flow out of your training muscles and look less red. In other words, the muscle circumference in normal time seems to be smaller than the muscle exercise time.
Let your boyfriend not only focus on chest exercises. It's really masculine on his chest. Even his chest is not really the most dazzling male part. Practice his shoulders and back, his waist, showing a three-dimensional inverted triangle effect, and then practice his abdomen into a washboard, which is really manly.