@article{, title = {Cardiovascular Responses to Orthostatic Stress in Endurance and Resistance Trained Athletes after Six Hours of Head-Down Bed Rest}, author = {B, Sinha}, abstract = { Introduction: Exercise training results in a number of cardiovascular adaptations specific to the nature of exercise program used. Endurance exercise training and resistance exercise training modulate the Cardiovascular System (CVS) differently. Endurance training is accompanied by a large increase in stroke volume and cardiac output during rest and exercise. Whereas, resistance training results in little to no change in cardiac output. The morphological and functional changes that occur during endurance training confer some advantages to athletic performance, however, endurance trained individuals are more prone to develop orthostatic hypotension during orthostatic stress. This intolerance becomes more prominent after an exposure to simulated microgravity condition. The similar cardiovascular deconditioning is not observed in resistance trained individuals. With an aim to examine the differences in CVS responses to orthostatic stress in endurance and resistance trained athletes, the present study was carried out where the individuals were subjected to 6-hr simulated microgravity condition in the form of Head-Down Bed Rest (HDBR). Methods: Healthy male volunteers from an army unit formed the study group. The participants were segregated into two subgroups i.e. Endurance Trained (ET) and Resistance Trained (RT), each consisting of 12 participants. In the first session, the baseline CVS response to orthostatic stress was measured by Head-Up Tilt Test (HUTT) in an automated tilt table at an angle of 70° from the horizontal position. Two days later, the participants were subjected to 6 hr of HDBR at an angle of -6° from the horizontal position. The Physiological parameters like Heart Rate (HR), Systolic Blood Pressure (SBP), Diastolic Blood Pressure (DBP), Mean Arterial Pressure (MAP) and Baroreflex Sensitivity (BRS) were recorded during HUTT before and after HDBR and were compared between two groups. Results: The Heart rate increased significantly during orthostatic stress from baseline supine in the ET group (34-39%) in comparison to the RT group (20-21%). The RT group had a significantly higher SBP, DBP and MAP during the post HDBR HUTT. The BRS was found to be reduced during orthostatic stress and becomes more pronounced in the ET group. There was also a decrease in BRS value in the ET group during a post HDBR orthostatic stress indicating of heightened sympathetic activity. Conclusion: Cardioacceleration, heightened sympathetic activity and a comparatively lower blood pressure during orthostatic stress may lead to more CVS deconditioning in endurance trained athletes as compared to resistance trained athletes. While selecting and imparting exercise training to astronauts, the importance of administering specific type of exercise regime should be considered carefully. }, volume = 62, journal = {Indian Journal of Aerospace Medicine}, issn = {0970-6666}, issn = {2582-5348}, }