Once we retire, we tend to bask in our newfound free time, but few of us realize that we should be spending part of that time exercising. Some fitness buffs may treat retirement as a chance to double up on their favorite activities, but for the rest of us, the challenge becomes extracting the most benefit in the least amount of time. Consistency is the key, said Michele Stanten, a certified fitness instructor in Coopersburg, Penn. Some people who are gung-ho at first try to do an hour of exercise, find its too much, and stop. Its more effective going out for 10 minutes one day, then 10 minutes the next day. Build up gradually and be consistent. Stanten consults with SilverSneakers, a free fitness program for seniors that comes with qualifying Medicare plans. It includes access to participating gyms at more than 14,000 locations across the U.S., along with instructor-led yoga, dance and other fitness classes. Regardless of your goalto gain muscle mass, lose body fat, lower your cholesterol,