Although by his own account Lambert did not eat unusually large amounts of food, at about the time of his return to Leicester his weight began to increase steadily, and by 1793, he weighed . Concerned for his fitness, in his spare time he devoted himself to exercise, building his strength to the point where he was able to easily carry . On one occasion, while he was watching a dancing bear on display in Blue Boar Lane, his dog slipped loose and bit it. The bear knocked the dog to the ground, and Lambert asked its keeper to restrain it so he could retrieve his wounded animal, but the keeper removed the bear's muzzle so it could attack the dog. Lambert reportedly struck the bear with a pole and with his left hand, punched its head, knocking it to the ground to allow the dog to escape.