SMITH, M. L. and P. B. RAVEN. Cardiovascular responses to lower body negative pressure in endurance and static exercise-trained men. Med. Sci. Sports Exerc., Vol. 18, No. 5, pp. 545-550, 1986. The cardiovascular responses to lower body negative pressure (LBNP) (to -50 torr) were examined in 8 sedentary control (UT), 8 endurance-trained (ET), and 8 weight-trained (WT) human subjects. The results were used to compare and contrast the blood pressure control system of the three subject groups. The primary differences in response included a more effective maintenance of blood pressure, by reason of greater stroke volume and cardiac indices of the WT subjects during LBNP (P < 0.05). Peripheral vascular resistances were not different (P > 0.05) throughout LBNP between the three groups. Therefore, the improved blood pressure maintenance of the WT subjects was attributed to a cardiac effect. The ET subjects were less effective in maintaining blood pressure than UT or WT subjects. This finding was apparently due to an attenuated baroreflex sensitivity, as evidenced by a significantly (P < 0.05) lower Δheart rate/Δsystemic blood pressure ratio, 0.99 for ET vs 1.51 and 1.38 for the UT and WT groups respectively, calculated from the responses observed from 0 to -50 torr of LBNP.
- Autonomic nervous system