Downtown workers and fitness fans can start Thursday and Friday off with a free morning workout from 6:30 to 7:30 a.m. at the Old State House. (The sessions are sponsored by USA Gymnastics and feature special appearances by former gymnastic champions and Olympians.)Thursday’s session features a boot camp and Pilates and Friday’s session includes boot camp exercise and yoga. There’ll also be a USA Gymnastics 50th Anniversary Pop Up Museum at the XL Center, Thursday through Sunday, Aug 15-18. Hours are 10 a.m. to 7 p.m. on Thursday, Friday and Saturday and 10 a.m.-5 p.m. on Sunday. Admission is free.