The present study was carried out at Centre for Sensory-Motor Interaction (SMI), Aalborg University, Denmark, and Roessingh Research and Development (RRD), Enschede, the Netherlands in the period from 2009 to 2012. I am most grateful to all co-authors for their contributions and for a fruitful collaboration. Especially, I wish to express my gratitude to Professor Pascal Madeleine and Miriam Vollenbroek- Hutten for their supervision and guidance to my projects. I would also like to thank all my colleagues at Centre for Sensory-Motor Interaction for providing a friendly, inspiring and competitive research environment. Further, I thank Dr. Heine Svarrer and Dr. Daan Wever for helping with inclusion of the specific patient groups in study III and IV. And a big thank you to all the participating volunteers, low-back pain patients and healthy subject, for showing patience and cooperating in the experiments of this PhD project. Finally, I would like to thank my lovely family who have supported me, encouraged me, and travelled with me to complete this project.