The flight instructor and private pilot were practicing a steep spiral that would terminate with a power-off landing. The instructor stated that the pilot had added "quite a bit" of elevator nose-up trim to maintain best glide speed during the spiral maneuver. Right before touchdown, the pilot sensed the airplane had a normal than higher descent rate and increased engine power. When power was added, the airplane’s nose pitched up and the airplane rolled “violently” to the left. The airplane’s left wing struck the runway, substantially damaging it. The flight instructor then assumed control of the airplane and reduced the engine power to idle as it departed the left side of the runway. The pilot subsequently taxied the airplane to the ramp uneventfully. Both pilots reported there were no mechanical malfunctions or failures of the airplane that would have precluded normal operation.