One of the biggest exercise myths is that you can lose fat in an area of the body by strength training or exercising that specific body part. The truth is that “spot reducing” and “spot toning” do not work, because we cannot dictate from where our bodies will decide to oxidize fat and we cannot change fat into muscle. Doing triceps press-downs will not decrease the amount of fat you have on the backs of your arms any more than doing crunches will decrease the amount of fat you have on your stomach.
As you age, your skin will become less elastic and thus conforms less to your arms. So “flabby arms” are somewhat a product of age. Any exercise that decreases body fat percentage will help you lose fat on your arms, just as it will help you lose fat from other areas of the body.
Idea Health and Fitness Association