By Richard Horgan Los Angeles (Knewz) — Here’s a statistic for you: 20 percent of the senior citizens who make up Tivity Health’s wonderfully named SilverSneakers Pulse ongoing survey say they are now back to working out on their own at the gym. Another 13 percent indicated they are attending group exercise classes at a gym, health club or community center, while three percent said they are partaking in an exercise class at a non-traditional venue. Overall, walking outdoors remains the most popular way for seniors to stay in shape, with 55 percent noting they currently do so. Then there’s the …