I love to work out but the older I get the more my muscles need prep time or post work out recovery. I have found these foam rollers are a terrific way to get blood flowing to trouble spots or achy areas of the body to promote muscle flexibility and recovery. Simply use these foam rollers a few minutes each day and you will be amazed with the enhanced flexibility and range of motion. The black rollers are the densest (hardest) but they also make blue ones which are slightly less dense and hard. For the money, you can't beat this simple way to help stay healthy.