Training mode does not affect orthostatic tolerance in chronically exercising subjects

Abstract

This study tested the hypotheses that trained swimmers would have greater orthostatic tolerance than runners and, if present, it would be due to differences in their autonomic and hemodynamic responses to graded central hypovolemia. Twenty intercollegiate male athletes [11 runners and 9 swimmers; .VO(2max) =70.0 (1.6) vs 69.5 (2.6) ml.kg(-1).min(-1), respectively] underwent graded lower body negative pressure (LBNP) to presyncope. The swimmers were heavier [80.5 (1.9) vs 70.3 (1.9) kg, P<0.05], with larger resting cardiac [4.44 (0.29) vs 3.68 (0.18) l.min(-1).m(-2)] and total peripheral conductance [0.056 (0.04) vs 0.044 (0.02) units.m(-2)] indices. Neither spontaneous cardiac baroreflex sensitivity (sequence method) nor heart rate variability (spectral analysis) differed significantly between groups at rest. LBNP tolerance did not differ between groups, with an index value of 51 (2) kPa.min for the runners and 54 (4) kPa.min for the swimmers [383 (16) vs 402 (32) mmHg.min], although the swimmers had larger declines in pulse pressure and tended ( P=0.078) to have larger declines in total peripheral conductance index in the last completed stage of LBNP. These responses did not differ between groups in the last 2 min of LBNP. Neither the heart rate, mean arterial pressure nor forearm vascular conductance responses differed between groups throughout. Changes in heart rate variability indices did not differ significantly between groups, with similar declines in the high frequency component and increases in the low frequency/high frequency ratio. These data suggest that swim training does not lead to greater orthostatic tolerance than run training, and responses to maximal LBNP do not differ between swimmers and runners. Moreover, neither heart rate nor the autonomic modulation of the heart rate response to LBNP are affected by training modality.

Artificial gravity with ergometric exercise as a countermeasure against cardiovascular deconditioning during 4 days of head-down bed rest in humans

“…One divided by the slope of the pressure-emptying curve represents venous Xow resistance (VFR). *P < 0.05 versus pre-HDBR of orthostatic tolerance (Franke et al 2003;Moore et al 2001). Therefore, it has been considered that AG with exercise training may be a more eVective countermeasure (Katayama et al 2004).…”

Swimming training increases cardiac vagal activity and induces cardiac hypertrophy in rats

“…Indeed, few studies comparing the effect of different endurance training modes on the autonomic nervous system have been conducted on other species. In humans, cardiac vagal tone analyzed by spectral analysis did not differ between runners and swimmers (22). In contrast, in running-trained mice, the resting bradycardia was associated with an increased cardiac vagal tone concomitantly with a decreased sympathetic tone (1), while in swimming-trained mice it was associated with a decreased cardiac sympathetic tone (Medeiros A and Brum PC, unpublished data).…”

Effects of a 6-mo endurance-training program on venous compliance and maximal lower body negative pressure in older men and women

“…In younger people, some cross-sectional investigations have shown that endurance-trained participants have lower tolerance to head-up tilt or lower body negative pressure (LBNP) (6,27), whereas others have found no fitness-related differences in tolerance (10,16). Longitudinal investigations have shown that exercise training has improved (5, 13), had no effect on orthostatic tolerance (4,33), or diminished tolerance to head-up tilt (26) and LBNP (28,36).…”

“…Calf venous compliance may be lower in older adults (17,19,23), which some have suggested may help protect older participants during orthostatic stress (19,38). Calf venous compliance is higher in endurance-trained young and older individuals (5,10,17,22,23). Tsutsui and colleagues (38) suggested that lower leg compliance was associated with higher orthostatic tolerance in old compared with the young participants.…”

“…In this context, the exercise group went from the 56th percentile in the 6-min walk test norms, which is what would be expected of a healthy older population, to the 84th percentile postintervention (29). It has been suggested that young participants with V O 2 peak Ͼ 55 (27) or 65 ml⅐ kg Ϫ1 ⅐ min Ϫ1 (4) are prone to reduced orthostatic tolerance, although this finding is not universally seen (10). This suggests that there might be a threshold of fitness for deleterious effects of increasing fitness on blood pressure regulation in response to orthostatic stress.…”