Arm strength is important on the run as your legs and feet follow your arms and hands. Keep your shoulders strong for a good swing. Make sure you swing from the shoulder and do not cross your arms in front of your body. Keep your hands relaxed in a cup shape (not clenched). If your arms and hands are relaxed, your legs and feet will follow allowing for a more fluid run.
We love these adjustable dumbbells from Rep Fitness. They take up very little space and are also very durable compared to other adjustable dumbbells on the market.