CARDIOVASCULAR-RESPONSE TO ORTHOSTATIC STRESS - EFFECTS OF EXERCISE TRAINING MODALITY

The effects of exercise training posture on cardiovascular and baroref lex responses to orthostatic challenge were assessed in highly trained cyclists (CT, n = 8) and swimmers (ST, n = 8), and in untrained men ( UT, n = 8). CT demonstrated the lowest orthostatic tolerance to lower body negative pressure (LBNP, a to -50 mmHg), with only 3 subjects com pleting the full LBNP procedure; 5 UT and all ST completed the testing . During LBNP, stroke volume (SV) decreases Mere similar in CT and ST, but greater than in UT. Mean pulse pressure and systemic vascular res istance (SVR) were reduced in CT relative to ST and UT at the highest levels of LBNP; the slope of the Delta SVR/Delta Z(0) and Delta SVR/De lta SV relationships in CT, used to assess peripheral vascular baroref lex function, were attenuated relative to the other groups. There were no between-group differences in the heart rate response to LBNP. The greater incidence of orthostatic intolerance observed in upright versu s supine-trained athletes during passive LBNP was linked to attenuated baroreflex control of peripheral vascular resistance.