He's the extremely buff actor who is known for his role of Thor in the successful Marvel franchise. And Chris Hemsworth took to social media on Friday to reveal the secret to maintaining his gruelling workouts, crediting it all to a book that he has written an introduction for. The 32-year-old  gushed about the tome, titled True To Form, by Dr. Eric Goodman, writing: 'If you've ever suffered from back pain or want a stronger healthier body then check this book out.' Read more: http://www.dailymail.co.uk/