Wednesday, November 9, 2016

Aerobic Exercise Training Improves Orthostatic Tolerance in Aging Humans.

Aerobic Exercise Training Improves Orthostatic Tolerance in Aging Humans.

Med Sci Sports Exerc. 2016 Nov 7;

Authors: Xu D, Wang H, Chen S, Ross S, Liu H, Olivencia-Yurvati A, Raven PB, Shi X

PURPOSE: This study was designed to test the hypothesis that aerobic exercise training of the elderly will increase aerobic fitness without compromising orthostatic tolerance (OT).
METHODS: Eight healthy sedentary volunteers (67.0±1.7 years old, 4 women) participated in 1-year of endurance exercise training (stationary bicycle and/or treadmill) program at the individuals' 65%-75% of peak heart rate (HRpeak). Peak O2 uptake (VO2peak) and HRpeak were determined by a maximal exercise stress test using a bicycle ergometer. Carotid baroreceptor reflex (CBR) control of HR and mean arterial pressure (MAP) were assessed by a neck pressure-neck suction (NP/NS) protocol. Each subject's maximal gain (Gmax), or sensitivity, of the CBR function curves were derived from fitting their reflex HR and MAP responses to the corresponding NP/NS stimuli using a logistic function curve. The subjects' OT was assessed using lower-body negative pressure (LBNP) graded to -50 mmHg; the sum of the product of LBNP intensity and time (mmHg•min) was calculated as the cumulative stress index (CSI).
RESULTS: Training increased VO2peak (before vs after: 22.8±0.92 vs 27.9±1.33 ml/min/kg, P < 0.01) and HRpeak (154±4 vs 159±3 beats/min, P < 0.02); and decreased resting HR (65±5 vs 59±5 beats/min, P < 0.02) and MAP (99±2 vs 87±2 mmHg, P < 0.05). CBR stimulus-response curves identified a leftward shift with an increase in CBR-HR Gmax (from -0.13±0.02 to -0.27±0.04 bpm/mmHg, P = 0.01). CSI was increased from 767±68 mmHg•min pre-training to 946±44 mmHg•min post-training (P < 0.05).
CONCLUSION: Aerobic exercise training improved the aerobic fitness and OT in elderly subjects. An improved OT is likely associated with an enhanced CBR function that has been reset to better maintain cerebral perfusion and cerebral tissue oxygenation during LBNP.


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