These five quick moves firm sagging arms after 55. After 55, declining muscle mass and reduced collagen make the upper arms appear softer, even if your weight hasn’t changed. Many people chase arm exercises that isolate only the biceps, but firmer arms depend on strengthening the triceps, shoulders, chest, and upper back together. Resistance Band Triceps Press-DownThe triceps make up roughly two-thirds of the upper arm, yet they’re often overlooked in favor of biceps curls. Using a resistance band instead of heavy weights allows for smooth resistance that’s easier on aging joints.