Lightweight dumbbells will improve mobility and strength in muscles and joints. There are many exercises that can be done seated with dumbbells, including biceps curls, triceps extensions and shoulder presses.
For bicep curls, hold one dumbbell in each hand, engage the core and plant feet firmly on the ground. Face palms toward the ceiling and slightly bend the elbow. Bring the weight toward your shoulder and slowly release to neutral. To work the triceps, turn the hands so the palms face inward. Bring the weights to chest level then, straighten the arms as you push straight back as far as you can, squeezing the triceps on full extension. For a gentle shoulder strengthener, hold weights just above the shoulders and press upward, extending the arms toward the ceiling, then release to neutral. Repeat 10 to 15 reps of each exercise.