Armstrong joins ride

Celebrity cyclist Lance Armstrong will ride the first leg of the Pan-Mass Challenge on Aug. 6 and 7. Pan-Mass announced his involvement yesterday, and within minutes, Armstrong was tweeting about the event. “Excited to be riding @panmassbike w/ all of you,’’ he tweeted to his almost 3 million followers. “Been trying to get there for years!’’ Armstrong added, “And psyched to be riding w/ @johnkerry as well. Take it easy on us Senator.’’ Senator John Kerry isn’t the only notable who’ll join Armstrong during the 32d annual ride from Sturbridge to Bourne. Other riders on the list include Senator Scott Brown, Jenny Johnson of “TV Diner,’’ New Balance CEO Rob DeMartini, and Red Sox wives Stacey Lucchino, Tiffany Ortiz, and Jacque Francona. The Pan-Mass Challenge raises money for cancer research and treatment at Dana-Farber. Armstrong, who retired from competitive cycling this year, ran the Boston Marathon in 2008.