Contents - 6 Acknowledgements - 8 Co-authors and their Current Affiliations - 10 1. Introduction - 12 2. Management of Vasovagal Syncope: Controlling or Aborting Faints by Leg Crossing and Muscle Tensing - 28 3. Leg Crossing, Muscle Tensing, Squatting and the "Crash-position" are Effective Against Vasovagal Reactions Through Increases in Cardiac Output - 40 4. Leg Crossing Improves Orthostatic Tolerance in Healthy Subjects: a Placebo Controlled Cross-over Study - 52 5. Lower Body Muscle Tensing Diminishes the Blood Pressure Decrease Upon Standing From Squatting in the Post-vasovagal State - 62 6. Management of Initial Orthostatic Hypotension: Lower Body Muscle Tensing Attenuates The Transient Arterial Blood Pressure Decrease Upon Standing From Squatting - 74 7. Conclusions - 84 Samenvatting (Dutch Summary) - 88 References - 92 Abbreviations - 110