The shot putter from Kamloops, B.C., leads the prestigious Diamond League standings and is No. 1 in the world rankings. Armstrong won gold at the 2007 Pan Am Games in Rio.
"The Pan American Games are an integral part of our national team program, however this year due to scheduling it is very difficult to send all of our best athletes," head coach Les Gramantik said Tuesday in a release. "The 2011 Pan American Games still represent an important stepping stone for many who have been selected to prove their abilities by competing and winning internationally."
Christie Gordon and Angela Whyte of Edmonton will race in the 100-metre hurdles. Crystal Smith of Kamloops and Sultana Frizell of Perth, Ont., will compete in the hammer throw and Krysha Bayley of Edmonton will be Canada's lone competitor in the long jump.
Winnipeg's Victoria Robson and Jason Wurster of Stevensville, Ont., will participate in the pole vault while Kate Van Buskirk of Brampton, Ont., and Malindi Elmore of Kelowna, B.C., will race in the 1,500 metres.
The Pan Ams mark the first major Games for young sprint star Christian Brennan of Waterdown, Ont. Brennan claimed three medals at the world youth championships earlier this season and set Canadian youth records in the 200 and 400 metres.
Other track competitors include Miana Griffiths of Oakville, Ont., Tremaine Harris of Markham, Ont., Kerri-Ann Mitchell of Pickering, Ont., Philip Osei of Toronto, Dontae Richards-Kwok of Mississauga, Ont., and Michael Robertson of Ottawa.
The Pan Am Games begin Oct. 14. Track and field events are scheduled for Oct. 23-29 at Telmex Athletics Stadium in Zapopan, Mexico.
Also Tuesday, Synchro Canada named its team for the Pan Ams. The duet competitions (technical and free) and team competitions (technical and free) in synchronized swimming are scheduled for Oct. 18-21 at Scotiabank Aquatics Center.
Marie-Pier Boudreau-Gagnon of Riviere-du-Loup, Que., and Elise Marcotte of L'Ancienne-Lorette, Que., are the Canadian duet pairing. They're joined on the team by Stephanie Durocher of Repentigny, Que, Jo-Annie Fortin of Montreal, Chloe Isaac of Brossard, Que., Stephanie Leclair of Gatineau, Que., Tracy Little of Pointe-Claire, Que., Karine Thomas of Gatineau and Valerie Welsh of Saint-Nicolas, Que.
The alternates are Genevieve Belanger of Laval, Que., Gabrielle Cardinal of Saint-Lambert, Que., and Erin Willson of Toronto.
The gold medallists in the duet and team events will qualify for the London Olympics next year.