Prolonged exercise following diuretic-induced hypohydration effects on fluid and electrolyte hormones.

To investigate the hypothesis that a reduction in plasma volume (PV) induced by diuretic administration would result in an increase in the fluid and electrolyte hormonal response to exercise, ten untrained males (VO(2) peak = 3.96 +/- 0.14 l/min) performed 60 min of cycle ergometry at 61 % VO(2) peak twice. The test was carried out once under control conditions (CON) (placebo) and once after 4 days of diuretic administration (DIU) (Novotriamazide; 100 mg triamterene and 50 mg hydrochlorothiazide). Calculated resting PV decreased by 14.6 +/- 3.3 % (p < 0.05) with DIU. No difference in plasma osmolality was observed between conditions. For the hormones measured, differences (p < 0.05) between conditions at rest were noted for plasma renin activity (PRA) (0.62 +/- 0.09 vs. 5.61 +/- 0.94 ng/ml/h), angiotensin I (ANG 1) (0.26 +/- 0.03 vs. 0.56 +/- 0.08 ng/ml), aldosterone (ALD) (143 +/- 14 vs. 1603 +/- 302 pg/ml), arginine vasopressin (AVP) (4.13 +/- 1.1 vs. 9.58 +/- 1.6 pg/ml) and atrial natriuretic peptide (alpha-ANP) (11.5 +/- 2.8 vs. 6.33 +/- 1.0 pg/ml). The exercise resulted in increases (p < 0.05) in PRA, ANG I, ALD, AVP, alpha-ANP. DIU led to higher levels of PRA, ANG I, and ALD (p < 0.05) and lower levels of alpha-ANP (p < 0.05) compared to CON. Arginine vasopressin was not affected by the loss of PV. For the catecholamines--norepinephrine (NE) and epinephrine (EPI)--only NE was higher during exercise with DIU compared to CON (p < 0.05). For PRA and ALD, the higher levels observed during exercise with DIU could be explained both by higher resting levels and a greater increase during exercise itself. For ANG I and NE, the effect of DIU only manifested itself during exercise. In contrast, the lower alpha-ANP observed during exercise with DIU was due to the lower resting levels. These results support the hypotheses that hypohydration leads to alterations in the secretion of all of the fluid and electrolyte hormones with the exception of AVP. The specific mechanisms of these alterations remain unclear, but appear to be related directly to the decrease in PV.     

Rehydration with glycerol: endocrine, cardiovascular, and thermoregulatory responses during exercise in the heat.

The impact of rehydration with glycerol on cardiovascular and thermoregulatory responses during exercise in the heat was studied in eight highly trained male cyclists. Each subject completed three dehydration-rehydration experimental trials that differed only in the rehydration treatment, each separated by 7 days. Before each experimental day, subjects dehydrated to -4% of their body weight by exercise and water restriction. The experimental treatments were as follows: no fluid (NF), glycerol bolus (1 g/kg body wt) followed by water (G), and water alone (W). Rehydration (3% body weight) was given over an 80-min period. After rehydration, subjects cycled (74% peak O2 uptake) to exhaustion in a hot and wet (37 degrees C and 48% relative humidity) environment. For G, plasma volume was expanded (P < 0.05) during rehydration and remained higher than W (P < 0.05) during exercise. Exercise time to exhaustion during G (33 +/- 4 min) was longer (P < 0.05) compared with both W (27 +/- 3 min) and NF (19 +/- 3 min). Cutaneous vascular conductance was significantly elevated (P < 0.05) during G, but G provided no other thermoregulatory or cardiovascular benefits compared with W and NF. Fluid-regulating hormones (vasopressin, aldosterone, atriopeptin, and plasma renin activity) decreased during rehydration and increased during exercise (except atriopeptin), but there were no differences between G and W. These data indicated that glycerol had little or no major effect on fluid-regulating factors during rehydration or exercise, and the improved exercise capacity in G was likely due to a greater plasma volume during exercise.     

Effect of prolonged physical exercise on fluid regulating hormones

Sixteen well-trained young men performed a test marathon to study the behaviour of atrial natriuretic peptide (ANP) and its second messenger cyclic guanosine monophosphate (cGMP) in relation to changes in plasma volume (PV) and plasma proteins, arginine vasopressin (AVP), renin, aldosterone, potassium and sodium. Blood samples were drawn under standardized conditions before and immediately after the run, as well as 3 h and 31 h after the run. Directly after the run, a two-and-a-half fold increase of plasma ANP and a twofold increase of plasma cGMP level were found, whereas PV decreased significantly by 7.4%. At this time renin-, aldosterone- and AVP-secretion were much stimulated. Thirty-one hours after the run, PV was markedly greater (10%) than before the race, whereas plasma proteins had returned to pre-exercise values. The ANP and cGMP were not significantly altered compared to the pre-race values. We have concluded that ANP and the other volume-regulating hormones may play an important role during and immediately after prolonged physical exercise but not in the longer recovery period. It seems that an influx of plasma proteins into the vascular space is responsible for the increased PV at this time.     

Untrained females: effects of submaximal exercise and heat on body fluids.

Five untrained females having no history of heat exposure worked in a cool (16-20 degrees C db, 28% rh) environment on day 1 and a warm environment on day 2 (45 degrees C db, 28% rh). Exercise level (bicycle ergometer) was 30% of individual Vo2 max values and work time on both days was 45 min. Venous blood samples were obtained at rest, after 40 min of exercise and 25 min after exercise ceased. Analysis of blood samples indicated an 8.3% increase in Hct during exercise on day 1 and a plasma volume reduction of 12.8% though total circulating protein increased 11.5%. Except for K+ all parameters approximated control values within 25 min postexercise. On day 2, exercise in heat caused a 12% increase in Hct and a plasma volume reduction of 17.7%. Mean total protein did not significantly change from resting values. These data indicated that for a given % Vo2 max, untrained females suffer considerably greater reductions in plasma volumes than do exercised males. Similar to males, dilatation of the cutaneous vascular bed in unacclimatized females resulted in loss of protein from the vascular volume.     

Sodium-free fluid ingestion decreases plasma sodium during exercise in the heat.

This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O2 consumption at 34 degrees C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (-2.48 +/- 2.25 vs. -0.86 +/- 1.61 mmol. l-1. h-1, P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time (R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease (R = -0. 478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.     

Hydration and vascular fluid shifts during exercise in the heat

This study examined the effects of hypohydration on plasma volume and red cell volume during rest in a comfortable (20 degrees C, 40% relative humidity) and exercise in a hot-dry (49 degrees C, 20% relative humidity) environment. A group of six male and six female volunteers [matched for maximal O2 uptake (VO2 max)] completed two test sessions following a 10-day heat acclimation program. One test session was completed when subjects were euhydrated and the other when subjects were hypohydrated (-5% from base-line body wt). The test sessions consisted of rest for 30 min in a 20 degrees C antechamber, followed by two 25-min bouts of treadmill walking (approximately 30% of VO2 max) in the heat, interspersed by 10 min of rest. No significant differences were found between the genders for the examined variables. At rest, hypohydration elicited a 5% decrease in plasma volume with less than 1% change in red cell volume. During exercise, plasma volume increased by 4% when subjects were euhydrated and decreased by 4% when subjects were hypohydrated. These percent changes in plasma volume values were significantly (P less than 0.01) different between the euhydration and hypohydration tests. Although red cell volume remained fairly constant during the euhydration test, these values were significantly (P less than 0.01) lower when hypohydrated during exercise. We conclude that hydration level alters vascular fluid shifts during exercise in a hot environment; hemodilution occurs when euhydrated and hemoconcentration when hypohydrated during light intensity exercise for this group of fit men and women.     

Energy metabolism and regulatory hormones in women and men during endurance exercise

Gender differences in the changes substrates of carbohydrate and lipid metabolism as well as in adrenaline, noradrenaline, growth hormone, insulin and cortisol were investigated in 24 women and 24 men during exhaustive endurance exercise. Training history and current performance capacity were taken into consideration in the design of the study. Since previous papers present conflicting results the purpose of the present study was to obtain further information regarding possible gender differences in lipid metabolism and its regulation by hormones. Non-endurance-trained women and men each ran 10 km on a treadmill at an intensity of 75% of VO2max; endurance-trained women and men ran 14 and 17 km, respectively, at an intensity of 80% of VO2max. Blood glucose levels in non-endurance-trained women were higher when compared to non-endurance-trained men. This might be explained by increased mobilization of free fatty acids from intramuscular fat depots during energy production in non-specifically trained women. In contrast, no substantial gender differences in endurance-trained persons were seen in lipid metabolism. The changes in substrates of lipid metabolism confirm the higher lipolytic activity and greater utilization of free fatty acids in endurance-trained persons. During endurance exercise, changes in adrenaline, noradrenaline, growth hormone, insulin and cortisol were not substantially affected by the sex of the subjects. This study does not present any conclusive results that endurance-trained persons show gender differences in lipid metabolism and major regulatory hormones.     

The Impact of heat exposure and repeated exercise on circulating stress hormones

To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age = 27.1 (3.0) years; maximal oxygen consumption, V˙O_2max = 47.6 (6.2) ml · kg · min⁻¹; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral (23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min bouts at ≈50% V˙O_2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3 h (CS and HS conditions). Blood samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E = 393 (199) pmol · l⁻¹ (CEx) vs 174 (85) pmol · l⁻¹ (CS), NE = 4593 (2640) pmol · l⁻¹ (CEx) vs 1548 (505) pmol · l⁻¹ (CS), and hGH = 274 (340) pmol · l⁻¹ (CEx)vs 64 (112) pmol · l⁻¹ (CS). At 40°C, bout 1: E = 596 (346) pmol · l⁻¹ (HEx) vs 323 (181) pmol · l⁻¹ (HS), NE = 7789 (5129) pmol · l⁻¹ (HEx) vs 1527 (605) pmol · l⁻¹ (HS), and hGH = 453 (494) pmol · l⁻¹ (HEx) vs 172 (355) pmol · l⁻¹ (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx = 364 (168) nmol · l⁻¹ vs HS = 295 (114) nmol · l⁻¹). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat (P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress, with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones to heat exposure and repeated moderate exercise. Accepted: 16 April 1997     

Hydration effects on thermoregulation and performance in the heat

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the blood. Aerobic exercise tasks are likely to be adversely effected by hypohydration (even in the absence of heat strain), with the potential affect being greater in hot environments. Hypohydration increases heat storage by reducing sweating rate and skin blood flow responses for a given core temperature. Hypertonicity and hypovolemia both contribute to reduced heat loss and increased heat storage. In addition, hypovolemia and the displacement of blood to the skin make it difficult to maintain central venous pressure and thus cardiac output to simultaneously support metabolism and thermoregulation. Hyperhydration provides no advantages over euhydration regarding thermoregulation and exercise performance in the heat.     

Vascular fluid shifts and endocrine responses to exercise in the heat. Effect of rehydration

This study examines the relationships between vascular changes and endocrine responses to prolonged exercise in the heat, associated with dehydration and rehydration by fluids of different osmolarity. Five subjects were exposed, in a 34 degrees C environment for 4 h of intermittent exercise on a cycle ergometer at 85 +/- 12 Watts (SD). Fluid regulatory hormones and cortisol were analysed in 3 experimental sessions: one without any fluid supplement (NO FLUID), and two with progressive rehydration, either by spring water (WATER) or isotonic solution (ISO), given after 70 min of exercise. Results were expressed in terms of differences between the mean values observed at the end of the exercise and the first hour values taken as references. Dehydration (NO FLUID) elicited a 4.0 +/- 0.8% (SE) decrease in plasma volume (PV) and an increase in osmolarity (8.4 +/- 3.1 mosmol X l-1). Concomitantly, plasma aldosterone (PA), renin activity (PRA), arginin vasopressin (AVP) and cortisol (PC) levels increased greatly in response to exercise in the heat (PA: 37.2 +/- 10.8 ng. 100 ml-1; PRA: 13.4 +/- 2.5 ng X ml-1 X h-1; AVP: 3.8 +/- 1.3 pg X ml-1; PC: 12.2 +/- 2.7 micrograms X 100 ml-1). Rehydration with water led to decreased osmolarity (-8.2 +/- 2.1 mosmol X l-1) with no significant changes in PV. With ISO, PV increased by 6.0 +/- 1.3% and the decrease in osmolarity was-5.8 +/- 1.8 mosmol X l-1. With both modes of rehydration, the increases in PRA, AVP and cortisol were blunted; only ISO prevented the rise in PA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diurnal effects of prior heat stress exposure on sprint and endurance exercise capacity in the heat

Active individuals often perform exercises in the heat following heat stress exposure (HSE) regardless of the time-of-day and its variation in body temperature. However, there is no information concerning the diurnal effects of a rise in body temperature after HSE on subsequent exercise performance in a hot environnment. This study therefore investigated the diurnal effects of prior HSE on both sprint and endurance exercise capacity in the heat. Eight male volunteers completed four trials which included sprint and endurance cycling tests at 30 °C and 50% relative humidity. At first, volunteers completed a 30-min pre-exercise routine (30-PR): a seated rest in a temperate environment in AM (AmR) or PM (PmR) (Rest trials); and a warm water immersion at 40 °C to induce a 1 °C increase in core temperature in AM (AmW) or PM (PmW) (HSE trials). Volunteers subsequently commenced exercise at 0800 h in AmR/AmW and at 1700 h in PmR/PmW. The sprint test determined a 10-sec maximal sprint power at 5 kp. Then, the endurance test was conducted to measure time to exhaustion at 60% peak oxygen uptake. Maximal sprint power was similar between trials (p = 0.787). Time to exhaustion in AmW (mean±SD; 15 ± 8 min) was less than AmR (38 ± 16 min; p < 0.01) and PmR (43 ± 24 min; p < 0.01) but similar with PmW (24 ± 9 min). Core temperature was higher from post 30-PR to 6 min into the endurance test in AmW and PmW than AmR and PmR (p < 0.05) and at post 30-PR and the start of the endurance test in PmR than AmR (p < 0.05). The rate of rise in core temperature during the endurance test was greater in AmR than AmW and PmW (p < 0.05). Mean skin temperature was higher from post 30-PR to 6 min into the endurance test in HSE trials than Rest trials (p < 0.05). Mean body temperature was higher from post 30-PR to 6 min into the endurance test in AmW and PmW than AmR and PmR (p < 0.05) and the start to 6 min into the endurance test in PmR than AmR (p < 0.05). Convective, radiant, dry and evaporative heat losses were greater on HSE trials than on Rest trials (p < 0.001). Heart rate and cutaneous vascular conductance were higher at post 30-PR in HSE trials than Rest trials (p < 0.05). Thermal sensation was higher from post 30-PR to the start of the endurance test in AmW and PmW than AmR and PmR (p < 0.05). Perceived exertion from the start to 6 min into the endurance test was higher in HSE trials than Rest trials (p < 0.05). This study demonstrates that an approximately 1 °C increase in core temperature by prior HSE has the diurnal effects on endurance exercise capacity but not on sprint exercise capacity in the heat. Moreover, prior HSE reduces endurance exercise capacity in AM, but not in PM. This reduction is associated with a large difference in pre-exercise core temperature between AM trials which is caused by a relatively lower body temperature in the morning due to the time-of-day variation and contributes to lengthening the attainment of high core temperature during exercise in AmR.     

Use of the glycemic index: effects on feeding patterns and exercise performance

The focus of this paper is on the glycemic index (GI) that provides effectual information on planning nutritional strategies for carbohydrate (CHO) supplementation in exercise. Related research has suggested that the GI can be used as a reference guide for the selection of an ideal CHO supplement in sports nutrition. Recently, the manipulation of GI of CHO supplementation in optimizing athletic performance has provided an exciting new research area in sports nutrition. There is a growing evidence to support the use of the GI in planning the nutritional strategies for CHO supplementation in sports. The optimum CHO availability for exercise has been demonstrated by manipulating the GI of CHO. Research has shown that a low GI CHO-rich meal is a suitable CHO source before prolonged exercise in order to promote the availability of the sustained CHO. In contrast, a high GI CHO-rich meal appears to be beneficial for glycogen storage after the exercise by promoting greater glucose and insulin responses. The prescribed feeding patterns of CHO intake during recovery and prior to exercise on glycogen re-synthesis and exercise metabolism have been studied in the literature. However, the studies on the subject are still limited, leaving some open questions waiting for further empirical evidences. The most significant question is whether CHO supplementation before and after exercise is beneficial when consumed as large feedings or as a series of snacks. Further research is needed on the effect of feeding patterns on exercise performance.     

Improvements in exercise performance: effects of carbohydrate feedings and diet

In an effort to determine the effects of carbohydrate (CHO) feedings immediately before exercise in both the fasted and fed state, 10 well-trained male cyclists [maximum O2 consumption (VO2 max), 4.35 +/- 0.11 l/min)] performed 45 min of cycling at 77% VO2 max followed by a 15-min performance ride on an isokinetic cycle ergometer. After a 12-h fast, subjects ingested 45 g of liquid carbohydrate (LCHO), solid carbohydrate confectionery bar (SCHO), or placebo (P) 5 min before exercise. An additional trial was performed in which a high-CHO meal (200 g) taken 4 h before exercise was combined with a confectionery bar feeding (M + SCHO) immediately before the activity. At 10 min of exercise, serum glucose values were elevated by 18 and 24% during SCHO and LCHO, respectively, compared with P. At 0 and 45 min no significant differences were observed in muscle glycogen concentration or total use between the four trials. Total work produced during the final 15 min of exercise was significantly greater (P less than 0.05) during M + SCHO (194,735 +/- 9,448 N X m), compared with all other trials and significantly greater (P less than 0.05) during LCHO and SCHO (175,204 +/- 11,780 and 176,013 +/- 10,465 N X m, respectively) than trial P (159,143 +/- 11,407 N X m). These results suggest that, under conditions when CHO stores are less than optimal, exercise performance is enhanced with the ingestion of 45 g of CHO 5 min before 1 h of intense cycling.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of heat and cold exposure and exercise on the interstitial fluid proteins of the rat

1. Interstitial fluid (obtained from capsules implanted subcutaneously) and plasma were obtained from rats before and after heat and cold exposure and exercise. 2. In the case of plasma, cold and heat exposure and exercise decreased A/G ratios. Albumin concentrations also decreased after heat and cold and protein concentration increased after exercise. 3. Cold decreased interstitial protein and albumin concentrations and A/G ratios. Heat exposure increased protein concentration and decreased the A/G ratio. Exercise decreased decreased protein concentrations. 4. The results are discussed in relation to previous findings.     

The effects of varying inertial loadings on power variables in the flywheel romanian deadlift exercise

The aim of this study was to investigate the effect of four different inertial loads (0.025, 0.050, 0.075, and 0.100 kg· m²) on concentric (CON) power, eccentric (ECC) power, and ECC overload in the flywheel Romanian deadlift (RDL). Fourteen recreationally trained males (27.9 ± 6.4 years, 90 ± 10.7 kg, 180.7 ± 5.5 cm) volunteered for the study. They had a minimum of two years of resistance training experience, although none had experience in flywheel inertia training (FIT). All participants performed the flywheel RDL on a flywheel device (kBox 3, Exxentric, AB TM, Bromma, Sweden). Each set was performed using different inertial loads, those being 0.025, 0.050, 0.075, and 0.100 kg·m². For CON, ECC power, and ECC overload, there was a significant difference (p < 0.001) between inertial loadings. In conclusion, results highlight that lower inertial load leads to higher peak CON and ECC power values, precisely 0.025 kg· m². Regarding ECC overload, medium to higher loads (0.050, 0.075, and 0.100 kg·m²) will lead to higher values.