Nico Hulkenberg has admitted he ended his test with Williams last week with a sore neck.
The British team's rookie racer for 2010 complied with the 'young driver' rules and therefore enjoyed two days at the wheel of the FW31 at Jerez.
Asked by Germany's Bild am Sonntag what he learned at the Spanish circuit, the 22-year-old jokingly answered: "That I have a neck."
Hulkenberg said "nothing can be compared" to the forces exerted on a racing driver by a F1 car.
The German said his manager Willi Weber's other client, Michael Schumacher, gave his old neck-training machine to Hulkenberg in order to prepare for the 2010 season.