Mr. Strautmanis made one — and only one — appointment with Mr. McClellan, just to satisfy the president. But Mr. Obama had other plans.

As Mr. Strautmanis walked away from a White House news conference one morning, the president caught up with him and called out, “Strautmanis, Cornell says you’re not showing up for your workouts.”

“And that’s when I knew this was going to be a different experience for me,” said Mr. Strautmanis, who has forsaken cheeseburgers, taken up egg whites and lost 20 pounds since he started twice-weekly sessions with Mr. McClellan in a gym at the Eisenhower Executive Office Building.