Cardiovascular and renal function during exercise-induced blood volume expansion in men.

To test the hypothesis that reduced baroreflex sensitivity is a direct result of exercise, we measured forearm vascular conductance (FVC) responses to graded lower body negative pressure (LBNP) 2, 20, and 44 h after intense exercise. Eight 4-min bouts of exercise at 85% of maximum oxygen uptake produced 3.5 +/- 0.7 and 3.9 +/- 1.0% blood volume (BV) expansions at 20 and 44 h of recovery, respectively. BV was unchanged from control values 2 h after exercise. The reduction in FVC was significantly less than control values during 30 and 40 mmHg of LBNP at 2 and 20 h of recovery, respectively, whereas heart rate and cardiac stroke volume responses were unchanged. Thus, a reduced FVC response to LBNP preceded BV expansion, demonstrating that exercise itself can elicit an attenuation of baroreflex function. To test the hypothesis that volume sensitivity of renal function is attenuated by intense exercise, we measured cardiovascular variables, plasma hormone concentrations, and renal output. At 20 h of recovery, resting mean arterial blood pressure and cardiac output were increased by 6 +/- 1 mmHg and 0.6 +/- 0.2 l/min, respectively, but resting plasma aldosterone and overnight Na+ excretion rate were unchanged. At 44 h of recovery, plasma aldosterone was decreased by 26 +/- 9% and overnight Na+ excretion rate was increased by 51 +/- 26%. Thus, appropriate endocrine and renal responses to increased BV were delayed until 44 h of recovery. Our findings suggest that a postexercise attenuation of baroreflex function participates in the induction of BV expansion by intense exercise.

Body fluid balance in dehydrated healthy older men: thirst and renal osmoregulation.

We examined osmotic control of thirst and free water clearance in healthy older (65+, n = 10) and younger (Y, n = 6) subjects during a 3-h rehydration period after an approximately 2.4% decrease in body weight. Plasma volume (PV), plasma osmolality (Posm), renal function, and thirst were measured before and after dehydration and during rehydration. In 65+, baseline PV was lower (43.1 +/- 1.6 vs. 48.1 +/- 2.5 ml/kg), Posm was higher (287 +/- 1 vs. 281 +/- 2 mosmol/kgH2O), and perceived thirst was lower than in Y. During dehydration, the osmotic threshold for increased thirst was shifted to a higher Posm in 65+. Total fluid intake was greater in Y than in 65+ (16.6 +/- 4.1 vs. 8.9 +/- 2.0 ml/kg); however, the relation between thirst and the rate of fluid intake was identical. Thus the blunted rehydration in 65+ is related to a lower overall sensation of thirst. The stimulus-response characteristics of osmotic control of free water clearance was similar in 65+ and Y; however, 65+ operated around a higher Posm and on a less-steep portion of the stimulus-response curve. These data support the hypothesis that the hyperosmotic hypovolemic state of healthy older individuals is not a result of a simple water deficit but represents a shift in the operating point for control of body fluid volume and composition.

Endocrine and performance responses to high volume training and amino acid supplementation in elite junior weightlifters.

To examine the effects of 1 week of high volume weightlifting and amino acid supplementation, 28 elite junior male weightlifters received either amino acid (protein) or lactose (placebo) capsules using double-blind procedures. Weightlifting test sessions were performed before and after 7 days of high volume training sessions. Serum concentrations of testosterone (Tes), cortisol (Cort), and growth hormone (GH) as well as whole blood lactate (HLa) were determined from blood draws. Lifting performance was not altered for either group after training, although vertical jump performance was not altered for either group after training, although vertical jump performance decreased for both groups. Both tests elicited significantly elevated exercise-induced hormonal and HLa concentrations. Significant decreases in postexercise hormonal and HLa concentrations from Test 1 to Test 2 were observed for both groups. Tes concentrations at 7 a.m. and preexercise decreased for both groups from Test 1 to Test 2, while the placebo group exhibited a decreased 7 a.m. Tes/Cort. These data suggest that amino acid supplementation does not influence resting or exercise-induced hormonal responses to 1 week of high volume weight training, but endocrine responses did suggest an impending over-training syndrome.

Acute hormonal responses in elite junior weightlifters.

To date, no published studies have demonstrated resistance exercise-induced increases in serum testosterone in adolescent males. Furthermore, few data are available on the effects of training experience and lifting performance on acute hormonal responses to weightlifting in young males. Twenty-eight junior elite male Olympic-style weightlifters (17.3 +/- 1.4 yrs) volunteered for the study. An acute weightlifting exercise protocol using moderate to high intensity loads and low volume, characteristic of many weightlifting training sessions, was examined. The exercise protocol was directed toward the training associated with the snatch lift weightlifting exercise. Blood samples were obtained from a superficial arm vein at 7 a.m. (for baseline measurements), and again at pre-exercise, 5 min post-, and 15 min post-exercise time points for determination of serum testosterone, cortisol, growth hormone, plasma beta-endorphin, and whole blood lactate. The exercise protocol elicited significant (p less than or equal to 0.05) increases in each of the hormones and whole blood lactate compared to pre-exercise measures. While not being significantly older, subsequent analysis revealed that subjects with greater than 2 years training experience exhibited significant exercise-induced increases in serum testosterone from pre-exercise to 5 min post-exercise (16.2 +/- 6.2 to 21.4 +/- 7.9 nmol.l-1), while those with less than or equal to 2 years training showed no significant serum testosterone differences. None of the other hormones or whole blood lactate appear to be influenced by training experience.(ABSTRACT TRUNCATED AT 250 WORDS)