Toronto 10-year-old Krystin Lavelle got a surprise on Tuesday when she accompanied her Uncle Rob to the gym at Marine Corps Base Hawaii: an autograph from U.S. President Barack Obama.

Obama is not her president but still, Lavelle was happy to score Obama's signature in her journal. Obama wrote, "To Krystin - Dream big dreams!" and his name.

Her Uncle Rob, a U.S. Navy officer who declined to give his last name to reporters, said the 52-year-old Obama, a noted gym rat, looked "very fit" during a Christmas Eve workout.

The president was doing free weights, followed by stretches, and finished with Pilates on the mat. Walking out of the gym Obama grabbed a basketball and shot a few baskets.

Reporters were not allowed to witness Obama's gym exploits but caught up with the Lavelles at a nearby McDonalds for a debriefing.

"His motorcade parked right up at the gym, and he made a beeline to the fence to greet people there," the Naval officer said. Obama, who was born in Hawaii, paid homage to his other hometown by sporting a Chicago White Sox baseball cap.

The Lavelles are vacationing at a home not far from the Obama family's upscale rental in Kailua, about 24 kilometres from Honolulu.

Krystin gave a flower to Obama, who said he would give it to his wife. "He said he'd tell her that he picked them," Lavelle said.