Incorporation of blood lactate and glucose into tissues in rats after short-term strenuous exercise

The purpose of this study was to investigate the main site of removal of blood lactate and glucose and which is the more important substrate for muscle glycogen resynthesis in rats after short-term strenuous exercise, to exhaustion. Male Wistar rats ran to exhaustion at a speed of 70-100m.min-1. Immediately after the exercise the rats received an injection of [U-14C]lactate (LA, 0.025 microCi.g-1, n = 5) or [U-14C]glucose (GL, 0.015 microCi.g-1, n = 5) into the aorta through an indwelling catheter. The rats were sacrificed after 40 min of recovery. During 40 min of recovery, 20.4% +/- 2.0% (mean +/- SE) of 14C injected was recovered as 14CO2 in LA, while 4.1% +/- 0.4% of 14C was recovered as 14CO2 in GL. In LA, the content of 14C incorporated per tissue weight in the vastus lateralis was significantly greater than that in the kidney, heart, and blood, while in GL that in the vastus lateralis was significantly greater than in any other tissues measured. The incorporation of 14C-glucose into muscle glycogen (vastus lateralis) was about five times greater than that of 14C-lactate. Data from this study indicate that lactate and glucose are incorporated from the blood into the skeletal muscle which was active during exercise and that blood glucose is a more preferred substrate for muscle glycogen resynthesis in rats after strenuous exercise to exhaustion.     

Plasma lactate recovery from maximal exercise with correction for variations in plasma volume

BACKGROUND: To compare plasma lactate concentrations and plasma lactate kinetics during recovery, for measured and corrected values for changes in plasma volume, after a maximal aerobic exercise. METHODS: Sixteen male subjects performed an incremental and maximal exercise in order to reach maximal aerobic power. Prior to the exercise, at the end and during recovery (2, 5, 12 and 30 min), blood samples were collected through an antecubital catheter. Samples were analysed for lactate, hematocrit and hemoglobin in order to calculate changes in plasma volume. Plasma lactate concentrations ([La]p) were corrected for changes in plasma volume. Plasma lactate kinetics was estimated through the ratio between [La]p after 5 min recovery minus [La]p after 30 min to time (25 min) and expressed in percentage per minute. RESULTS: Maximal changes in plasma volume (-19.7 +/- 3.8%) were correlated to maximal measured [La]p (r=0.66, p<0.01). Maximal measured [La]p values (14.9 +/- 2.6 mmol x l-1) were 17.3% higher (p<0.001) than corrected values (12.7 +/-2.0 mmol x l-1). The kinetics of [La]p decrease was significantly higher (p<0.001) for measured values (2.38 +/- 0.29 % x min-1) than for corrected values (2.22 +/- 0.33 % x min-1). CONCLUSIONS: These results suggested that changes in plasma volume must be taken into account when peak postexercise plasma lactate concentration or lactate recovery curves are analysed.     

Effect of caffeine on glycogenolysis during exercise in endurance trained rats

Caffeine has been reported to enhance performance by increasing lipid oxidation and sparing liver and muscle glycogen in human subjects during prolonged endurance exercise. In the present study, the effects of intravenous caffeine on the liver and muscle glycogenolysis during exercise in endurance trained rats were investigated. Male endurance trained rats (2 h.d-1 for 6-7 wk) were given injections of 5 mg.kg-1 caffeine (5 CAF), 25 mg.kg-1 caffeine (25 CAF), or 0.9% sodium chloride (SAL) and were run on the treadmill for 45 min, 90 min, or until exhaustion at 26 m.min-1 up a 15% grade. Intravenous caffeine did not enhance the endurance run time: 5 CAF = 149 +/- 14 min, 25 CAF = 152 +/- 10 min, and SAL = 176 +/- 10 min. Caffeine did not influence the rate of liver glycogenolysis during exercise [liver glycogen (mmol glucose units.g-1) after 90 min: 5 CAF = 139 +/- 26, 25 CAF = 133 +/- 25, and SAL = 120 +/- 32]. Liver cAMP, muscle glycogen, plasma free fatty acids, blood glucose, and lactate were likewise not affected by caffeine [plasma free fatty acids (mM) after 90 min: 5 CAF = 0.42 +/- 0.04, 25 CAF = 0.45 +/- 0.07, and SAL = 0.41 +/- 0.05]. These data indicate that intravenous caffeine does not enhance the endurance run time or alter the plasma free fatty acids or liver and muscle glycogen utilization in endurance trained rats.     

Endurance improved by ingestion of a glucose polymer supplement

The effect of glucose polymer (GP) ingestion upon endurance performance during walking exercise at 45% VO2max was examined. Also, performance on a battery of psychomotor tests was assessed to determine if exhaustion from endurance exercise was related to central nervous system dysfunction. Ten trained male subjects ingested approximately 120 g of GP in four equally-divided dosages 60, 90, 120, and 150 min following the start of exercise. This treatment significantly increased time to exhaustion by 11.5% as compared to the control (C) group (GP=299.0 +/- 9.8 min; C=268.3 +/- 11.8 min). No difference in VO2 (1 X min-1) or perceived exertion was noted between treatments. As a result of the GP feedings the rate of carbohydrate utilization during the GP trial was 0.53 g X min-1 greater than during the C trial. However, during the GP trial plasma glucose did not fall below the pre-exercise level and was significantly higher than the C plasma glucose concentration at exhaustion. No differences in psychomotor performance between treatments or between rested and exhausted states for either the C or GP treatments were noted. These data suggest that exhaustion was not a result of hypoglycemia or central nervous system dysfunction and that glucose polymer supplements may enhance endurance capacity.     

Prolonged exercise in highly trained female endurance runners

The effects of prolonged exercise in a 21 degree C dry bulb and 15 degree C wet bulb environment at 65%-70% VO2max were examined in seven highly trained females. The subjects, aged 22-35 years, underwent an initial incremental treadmill test to exhaustion, with assessment of VO2max and related cardiorespiratory variables. One week later, under similar environmental conditions, subjects ran at approximately 65% VO2max for 80 min on a motor-driven treadmill. Approximately 10 ml of venous blood was withdrawn 10 min prior and immediately prior to the onset of prolonged exercise, and at 20, 40, 60, and 80 min, and 20 min post-exercise. Venous blood was analyzed for glucose, lactate, osmolality, Na+, K+, protein, and hemoglobin (Hb). Hematocrit was measured and changes in plasma volume calculated. VO2, VE, respiratory exchange ratio, and heart rate were recorded at 17, 37, and 77 min. The percent body fat estimated from skinfold thicknesses was 19 +/- 1%. The mean VO2max was 59.3 +/- 1.0 ml . kg-1 . min-1, with a mean max VE STPD and heart rate of 78.75 +/- 3.10 1 . min-1 and 175 +/- 4 beats . min-1, respectively. No significant changes occurred in VO2, VE, % VO2max, heart rate, venous lactate, plasma glucose, or plasma protein during the prolonged exercise. A significant decrease in respiratory exchange ratio was noted. Significant changes also occurred in hematocrit, Hb, Na+, K+, and osmolality. An interesting finding was the pre-exercise expansion of the plasma volume.     

Pre-exercise feeding does not affect endurance cycle exercise but attenuates post-exercise starvation-like response

The effects of ingesting a mixed-snack food (CB), fructose (FRU), or placebo (PBO) prior to exercise (70% peak VO2) on the metabolic response during and after cycle exercise were studied in eight normal healthy volunteers with a wide range of peak VO2 (30-70 cc.kg-1.min-1). The study was designed to minimize the impact of confounding factors by using various strategies. First, the volunteers were grouped in teams with stratification by peak VO2, and the tests were randomized by a Latin-square design. Second, subjects received two acclimation trials in the cycle ergometer to diminish the effect of learning experiences and allow them to get used to the room and equipment. In addition, financial incentives were offered for team and individual endurance times. The test meals were administered 30 min prior to the beginning of exercise, and the subjects exercised to exhaustion, which was defined with clear-cut endpoints. Gas and blood samples were taken at regular intervals before, during, and for 60 min after each exercise bout. CB and FRU induced higher pre-exercise glucose and insulin concentrations. Blood lactate increased 100% with FRU ingestion. Despite these differences; endurance time, substrate, and hormone concentrations as well as rates of substrate oxidation during exercise were identical among the three conditions. During the post-exercise recovery period, PBO was associated with a starvation-like pattern of substrate utilization in which lipid oxidation was 60% greater and carbohydrate oxidation 50% less than following either CB (75 +/- 11, 248 +/- 27 mg.min-1, P less than 0.05) or F ingestion (93 +/- 4, 221 +/- 14 mg.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic and hormonal responses to lipid and carbohydrate diets during exercise in man

Nine healthy subjects were studied to determine their performance and the metabolic and hormonal responses to prolonged exercise after ingestion of a carbohydrate or a lipid diet. Subjects exercised on a bicycle ergometer (60% VO2max) until exhaustion four times at weekly intervals. The exercise test was performed 1 h after ingestion of three different isocaloric meals (400 Kcal) containing either glucose, medium-chain triglycerides (MCTs) or long-chain triglycerides (LCTs). The fourth test was performed after a night fast. The metabolism of these nutriments was followed using [U-13C]glucose, [1-13C]octanoate, and [1-13C]palmitate added as tracers. The average work time was comparable whatever nutriment used (116 +/- 11 min). Oxidation of the ingested nutriment over this period was 80% for glucose, 45% for MCTs, and 9% for LCTs. Glucose ingestion produced an early insulin peak associated at the end of the exercise with a lower glycemia compared to the fat diets. After MCT ingestion, an increase in ketone bodies was observed. Catecholamine response to physical exercise was decreased by all the meals when compared to fasting. Thus, we conclude that a different lipid meal, MCTs, or LCTs, compared to glucose feeding, do not modify exhaustion time in spite of differences in hormonal and metabolic responses.     

Prior heavy exercise enhances performance during subsequent perimaximal exercise

PURPOSE: To test the hypothesis that prior heavy exercise increases the time to exhaustion during subsequent perimaximal exercise. METHODS: Seven healthy males (mean +/- SD 27 +/- 3 yr; 78.4 +/- 0.7 kg) completed square-wave transitions from unloaded cycling to work rates equivalent to 100, 110, and 120% of the work rate at VO2peak (W-[VO2peak) after no prior exercise (control, C) and 10 min after a 6-min bout of heavy exercise at 50% Delta (HE; half-way between the gas exchange threshold (GET) and VO2peak), in a counterbalanced design. RESULTS: Blood [lactate] was significantly elevated before the onset of the perimaximal exercise bouts after prior HE (approximately 2.5 vs approximately 1.1 mM; P < 0.05). Prior HE increased time to exhaustion at 100% (mean +/- SEM. C: 386 +/- 92 vs HE: 613 +/- 161 s), 110% (C: 218 +/- 26 vs HE: 284 +/- 47 s), and 120% (C: 139 +/- 18 vs HE: 180 +/- 29 s) of W-VO2peak, (all P < 0.01). VO2 was significantly higher at 1 min into exercise after prior HE at 110% W-VO2peak (C: 3.11 +/- 0.14 vs HE: 3.42 +/- 0.16 L x min(-1); P < 0.05), and at 1 min into exercise (C: 3.25 +/- 0.12 vs HE: 3.67 +/- 0.15; P < 0.01) and at exhaustion (C: 3.60 +/- 0.08 vs HE: 3.95 +/- 0.12 L x min(-1); P < 0.01) at 120% of W-VO2peak. CONCLUSIONS: This study demonstrate that prior HE, which caused a significant elevation of blood [lactate], resulted in an increased time to exhaustion during subsequent perimaximal exercise presumably by enabling a greater aerobic contribution to the energy requirement of exercise.     

Hepatic UDP-glucose 13C isotopomers from [U-13C]glucose: a simple analysis by 13C NMR of urinary menthol glucuronide.

Menthol glucuronide was isolated from the urine of a healthy 70-kg female subject following ingestion of 400 mg of peppermint oil and 6 g of 99% [U-(13)C]glucose. Glucuronide (13)C-excess enrichment levels were 4-6% and thus provided high signal-to-noise ratios (SNRs) for confident assignment of (13)C-(13)C spin-coupled multiplet components within each (13)C resonance by (13)C NMR. The [U-(13)C]glucuronide isotopomer derived via direct pathway conversion of [U-(13)C]glucose to [U-(13)C]UDP-glucose was resolved from [1,2,3-(13)C(3)]- and [1,2-(13)C(2)]glucuronide isotopomers derived via Cori cycle or indirect pathway metabolism of [U-(13)C]glucose. In a second study, a group of four overnight-fasted patients (63 +/- 10 kg) with severe heart failure were given peppermint oil and infused with [U-(13)C]glucose for 4 hr (14 mg/kg prime, 0.12 mg/kg/min constant infusion) resulting in a steady-state plasma [U-(13)C]glucose enrichment of 4.6% +/- 0.6%. Menthol glucuronide was harvested and glucuronide (13)C-isotopomers were analyzed by (13)C NMR. [U-(13)C]glucuronide enrichment was 0.6% +/- 0.1%, and the sum of [1,2,3-(13)C(3)] and [1,2-(13)C(2)]glucuronide enrichments was 0.9% +/- 0.2%. From these data, flux of plasma glucose to hepatic UDPG was estimated to be 15% +/- 4% that of endogenous glucose production (EGP), and the Cori cycle accounted for at least 32% +/- 10% of GP.     

力竭运动过程中大鼠纹状体葡萄糖/乳酸代谢的实时观察

目的:通过实时观察一次性力竭运动过程中大鼠纹状体葡萄糖和乳酸浓度的动态变化规律,揭示运动性中枢疲劳形成过程中脑能量代谢的特征。方法:8周龄雄性Wistar大鼠20只分为两组,纹状体葡萄糖、乳酸测定组(第1组)和外周血葡萄糖、乳酸测定组(第2组),每组10只。采用微透析-电化学联用的活体检测技术,实时监测大鼠(第1组)在一次性力竭运动过程中纹状体细胞外液中葡萄糖和乳酸的代谢变化,并从尾静脉采血动态监测大鼠(第2组)外周血液中葡萄糖和乳酸浓度的变化。结果:(1)与安静状态相比,运动初期大鼠纹状体胞外乳酸浓度显著升高(P<0.05),运动后期直至恢复期均显著降低(P<0.05,P<0.01);而胞外葡萄糖浓度在运动初期无明显变化,在运动后期开始下降,甚至在恢复期的90分钟内仍显著低于安静水平(P<0.05,P<0.01)。(2)大鼠外周血糖浓度随着运动时间的延长而显著降低,在运动力竭以及恢复期血糖水平均显著低于安静水平(P<0.05,P<0.01);大鼠血乳酸浓度在力竭运动过程中显著高于安静时水平(P<0.05),而在运动结束后即迅速恢复至安静时水平。结论:力竭运动过程中,持续的外周低血糖导致脑对于葡萄糖摄取不足,出现脑葡萄糖和乳酸浓度降低,中枢能量物质葡萄糖和乳酸代谢的显著降低可能是产生运动性中枢疲劳的一个重要的神经生物学机制。     

Tennis: a physiological profile during match play.

Heart rate (HR), hematocrit, hemoglobin, blood glucose, and plasma concentrations of lactate, cortisol, and testosterone were monitored in 10 male subjects (Division I, 20.3 +/- 2.5 yrs, VO2max: 58.5 +/- 9.4 ml.kg-1.min-1) during singles tennis and a treadmill test. During the on-court session, HR was 144.6 +/- 13.2 beats.min-1 for the 85 min of play. Plasma lactate rose 50% from a post-warmup value of 1.6 +/- 0.6 mmol.l-1 to 2.3 +/- 1.2 mmol.l-1 during play (p greater than 0.05). Blood glucose slightly decreased (8%, p greater than 0.05) from a pre-exercise value of 4.6 +/- 0.8 mmol.l-1 as a result of the 10-min warmup. This was followed by a 23% rise (p less than 0.05) from 4.2 +/- 1.0 mmol.l-1 to 5.2 +/- 0.6 mmol.l-1, measured after the first 30 min of play. Blood glucose subsequently remained steady at slightly above the pre-exercise value. Plasma cortisol rose (9%, p greater than 0.05) during the warmup and subsequently decreased (p less than 0.05) from a post-warmup value of 558.2 +/- 285.2 nmol.l-1 to 337.1 +/- 173.3 nmol.l-1 (a 40% decrease), and remained decreased during recovery. Plasma testosterone rose 22% (p less than 0.05) from pre-exercise to recovery (13.5 +/- 3.8 nmol.l-1 and 16.5 +/- 2.6 nmol.l-1, respectively). Although tennis is characterized by periods of high-intensity exercise, the overall metabolic response resembles prolonged moderate-intensity exercise.     

Effects of acute cold exposure on submaximal endurance performance

The purposes of this study were to assess VO2max and submaximal endurance time to exhaustion (ET) during acute cold-air exposure. Eight male subjects (means age = 19.9 yr) were alternately exposed in groups of four to chamber temperatures of +20 degrees C and -20 degrees C for 30 h each. A week was allowed between exposures. Maximum oxygen uptake was measured using a mechanically-braked cycle ergometer, and ET was determined on the same ergometer using a 17-min/3-min exercise/rest schedule until the subject was unable to maintain pedal rate. Maximum oxygen uptake was not significantly different between conditions: 3.43 +/- 0.09 l X min-1 at +20 degrees C and 3.35 +/- 0.10 l X min-1 at -20 degrees C. During endurance exercise, intensities equaled 77.1 +/- 1.4% and 78.9 +/- 2.0% of VO2max at +20 degrees C and -20 degrees C, respectively. Heart rate and VO2 values obtained between 8 and 10 min of the endurance run were not significantly different (156 +/- 2 bpm and 2.63 +/- 0.08 l X min-1 at +20 degrees C and 158 +/- 3 bpm and 2.65 +/- 0.11 l X min-1 at -20 degrees C). Endurance time to exhaustion however, decreased 38% (P less than 0.05) from 111.9 +/- 22.8 min at +20 degrees C to 66.9 +/- 13.6 min at -20 degrees C. The data support the contention that aerobic capacity is not altered by cold exposure but suggest a marked decrease in submaximal endurance performance.     

Blood lactate threshold differences between arterialized and venous blood

The purpose of this study was to investigate the differences between lactate thresholds determined from venous and arterialized blood. Seven endurance-trained college males performed an incremental bicycle ergometer exercise test until exhaustion. At the end of each 3 min stage, blood was sampled simultaneously from a hyperemized ear-lobe and an antecubital vein for the measurement of blood lactate (La-). Two-minute rest intervals separated each stage. Arterialized blood La-concentrations ([La-]) were significantly higher than venous blood at 350 W (14.5 and 9.7 mmol.l-1), maximal exercise (15.5 and 11.39 mmol.l-1), and throughout recovery. Arterialized [La-] was significantly higher than venous blood at the onset of blood La- accumulation (OBLA) (4.0 and 2.8 +/- 0.1 mmol.l-1), the individual anaerobic threshold (IAT) (3.4 +/- 0.3 and 2.1 +/- 0.1 mmol.l-1), and the ventilatory threshold (VT) (4.7 +/- 0.9 and 3.2 +/- 0.6 mmol.l-1). No significant differences were found between either La-threshold for arterialized or venous blood. The oxygen consumption (VO2) at OBLA was significantly lower when determined from arterialized blood La (2.3 +/- 0.2 and 2.8 +/- 0.2 l.min-1). No significant differences existed between the LT, OBLA, and IAT threshold-VO2 determinations from arterialized blood; however, significant differences were found between IAT-OBLA (2.1 +/- 0.2 and 2.8 +/- 0.2 l.min-1) and LT (2.2 +/- 0.2 l.min-1)-OBLA from venous blood. These results indicate that differences between venous and arterialized blood [La-] need to be considered when comparing different anaerobic threshold determinations.     

Passive versus active recovery during high-intensity intermittent exercises

PURPOSE: To compare the effects of passive versus active recovery on muscle oxygenation and on the time to exhaustion for high-intensity intermittent exercises. METHODS: Twelve male subjects performed a graded test and two intermittent exercises to exhaustion. The intermittent exercises (15 s) were alternated with recovery periods (15 s), which were either passive or active recovery at 40% of .VO2max. Oxyhemoglobin was evaluated by near-infrared spectroscopy during the two intermittent exercises. RESULTS: Time to exhaustion for intermittent exercise alternated with passive recovery (962 +/- 314 s) was significantly longer (P < 0.001) than with active recovery (427 +/- 118 s). The mean metabolic power during intermittent exercise alternated with passive recovery (48.9 +/- 4.9 mL.kg-1.min-1) was significantly lower (P < 0.001) than during intermittent exercise alternated with active recovery (52.6 +/- 4.6 mL.kg-1.min-1). The mean rate of decrease in oxyhemoglobin during intermittent exercises alternated with passive recovery (2.9 +/- 2.4%.s-1) was significantly slower (P < 0.001) than during intermittent exercises alternated with active recovery (7.8 +/- 3.4%.s-1), and both were negatively correlated with the times to exhaustion (r = 0.67, P < 0.05 and r = 0.81, P < 0.05, respectively). CONCLUSION: The longer time to exhaustion for intermittent exercise alternated with passive recovery could be linked to lower metabolic power. As intermittent exercise alternated with passive recovery is characterized by a slower decline in oxyhemoglobin than during intermittent exercise alternated with active recovery at 40% of .VO2max, it may also allow a higher reoxygenation of myoglobin and a higher phosphorylcreatine resynthesis, and thus contribute to a longer time to exhaustion.     

Effects of acute prednisolone intake during intense submaximal exercise

To study the effects of a therapeutical dose of corticosteroid alone or associated with beta-2 agonist on performance and substrate response during intense submaximal exercise, seven healthy moderately trained male volunteers participated in the double-blind randomized cross-over study. An intense endurance exercise test to exhaustion was performed after ingestion of placebo (Pla), 20 mg prednisolone (Pred), and 20 mg prednisolone plus 4 mg salbutamol (Pred-Sal). Blood samples were collected at rest, after 5, 10 min of exercise, at exhaustion, and after 5 (r5), 10 (r10), and 20 (r20) min of passive recovery for ACTH, growth hormone, insulin, blood glucose, and lactate measurements. There were no significant differences in exercise time to exhaustion between the three treatments (Pla: 21.5 +/- 2.9; Pred: 22.0 +/- 2.5; Pred-Sal: 24.2 +/- 2.8 min). ACTH was significantly lowered after Pred and Pred-Sal vs. Pla from the start of exercise to the end of the experiment (p < 0.05). Pred and Pred-Sal increased resting and recovery (r10 and r20) significantly but not exercise blood glucose values. There were no significant differences in growth hormone concentrations between the three treatments whereas insulin was significantly higher at rest, during exercise, and at r20 after Pred-Sal administration vs. Pred and Pla (p < 0.05). Pred and Pred-Sal showed no significant effect on blood lactate compared with Pla treatment. These preliminary results do not support the hypothesis that acute oral therapeutic corticosteroid intake alone or associated with beta-2 mimetic improves performance during intense submaximal exercise, but further studies are necessary with tests of longer duration.     

Effect of branched-chain amino acids (BCAA), glucose, and glucose plus BCAA on endurance performance in rats

PURPOSE: The purpose of this study was to assess the effects of pre-exercise administration of branched-chain amino acids (BCAA), glucose, and glucose plus BCAA on time to exhaustion during treadmill exercise in rats. METHODS: Wistar rats were injected intraperitoneally with 1 mL of saline (0.9% NaCl), BCAA (30 mg), glucose (100 mg), or glucose plus BCAA 5 min before either 45 min of submaximal exercise (N = 32) or running to exhaustion (N = 24). After the submaximal exercise test, blood was collected for the measurement of ammonia, BCAA, free tryptophan (free TRP), glucose, free fatty acid, and lactic acid, and muscle samples were taken from the m. soleus for determination of glycogen content. RESULTS: Mean run time to exhaustion was significantly longer after BCAA administration (158+/-26 min) compared with that after saline (118+/-35 min)(P<0.05) but not compared with that after glucose administration (179+/-21 min). When glucose is administered before exercise, the supplementary administration of BCAA had no additional effect on performance (171+/-12 min). The data on blood ammonia, ratio of free TRP/BCAA, and muscle glycogen did not provide a clue for explaining the higher endurance performance after BCAA supplementation. CONCLUSION: The results support the hypothesis that the effect of BCAA administration on performance could be related to carbohydrate availability during exercise.     

Blood biochemical status of miniature swine during submaximal and exhaustive exercise

Simultaneous arterial (left atrial) and mixed venous (right atrial) blood samples were anaerobically drawn from 14 miniature swine (mean weight = 25.0 +/- 1.7 [SE] kg) in order to examine the adequacy of these animals as a model for the exercising human. Samples were drawn: 1) at rest; 2) during exercise that elicited 80.4 +/- 1.2% of the animals' measured maximal heart rates; 3) at exhaustion; and 4) during the 4th min of a standing, resting recovery period. At rest, the animals were mildly alkalotic (pHa = 7.497 +/- 0.016) and hypocapnic (pCO2a = 29.6 +/- 1.2 torr), with low hematological values (arterial hemoglobin = 6.66 +/- 0.18 mmol X 1-1; arterial hematocrit = 32.0 +/- 0.9%) and slightly elevated catecholamine concentrations. During the submaximal exercise, there were no statistically significant changes in the arterial blood pH or in plasma sodium (Na+) and chloride (Cl-) concentrations, with significant decreases observed in Hcta, pCO2a, and increases in arterial plasma norepinephrine, total protein, and potassium (K+) concentrations. At exhaustion, pHa and pCO2a decreased further, with increases noted in the arterial plasma concentrations of K+, epinephrine, total protein, and the Hct but not in Na+ or Cl-. During recovery, arterial lactate averaged 20.54 +/- 0.71 mmol X 1-1. Venous changes were similar to those observed in arterial blood, with a mean pHv of 7.168 +/- 0.043 and arterial lactate = 21.08 +/- 0.90 mmol X 1-1 during recovery. Exercise-induced hemoconcentration was similar for both arterial and venous sample sites during both the submaximal and exhaustive exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of beta-adrenergic blockade on supramaximal exercise capacity

Fourteen male physical education students performed a single bout of running until exhaustion on the treadmill at 22 km/h and 7.5% slope. They received single oral doses of 100 mg bupranolol (nonselective beta-blockade), 100 mg metoprolol (beta-1-selective blockade), and placebo 60-90 min before running. Arterialized capillary blood was sampled repeatedly until 30 min after exercise for assessment of lactate and glucose. Adrenaline and noradrenaline were determined in venous plasma before and immediately after exercise. Running time until exhaustion was 49.3 +/- 2.3 s in the control experiment, 44.5 +/- 2.0 s with metoprolol, and 42.7 +/- 2.0 s with bupranolol. The reductions under beta-blockade were statistically significant. With both beta-blockers the increases of the lactate and glucose blood levels were significantly reduced, the levels being almost identical with metoprolol and bupranolol. The post-exercise levels of adrenaline and noradrenaline did not differ significantly between the control, metoprolol, and bupranolol experiments. It is concluded that determination of the lactate and glucose levels in blood did not allow assessment of the mechanism by which beta-blockade impairs the capacity for supramaximal exercise. Besides reduced anaerobic energy release due to inhibition of glycogenolysis, other beta-blocker effects are considered.     

Effects of short-term prednisolone intake during submaximal exercise

PURPOSE: To examine the prednisolone's ergogenic and metabolic effects during submaximal exercise. METHODS: Ten recreational male athletes completed two cycling trials at 70-75% peak O2 consumption until exhaustion after either placebo (Pla, lactose) or oral prednisolone (Pred, 60 mg.d(-1) for 1 wk) treatment, according to a double-blind and randomized protocol. Blood samples were collected at rest and during exercise and recovery to determine ACTH, growth hormone (GH), prolactin (PRL), DHEA, insulin, blood glucose, and blood lactate values. RESULTS: Time of cycling was significantly increased after chronic Pred treatment (Pred: 74.5+/-9.5 min; Pla: 46.1+/-3.3 min, P<0.01). Pred intake significantly lowered basal, exercise, and recovery ACTH, DHEA, and PRL concentrations, whereas GH concentrations were significantly lowered by Pred after 30 min of exercise. Blood glucose and insulin were significantly (P<0.05) increased by Pred during the whole experiment and until 30 min of exercise. Blood lactate concentrations were higher after Pred versus Pla at 10 min of exercise until 10 min of recovery (P<0.05). CONCLUSION: From these data, short-term Pred intake did seem to significantly improve performance during submaximal exercise, with concomitant alterations in hormonal and metabolic responses. Further studies will be necessary to elucidate the mechanisms of these hormonal and metabolic changes, and to determine whether the changes may be associated with the marked performance improvement obtained.     

Incremental test protocol, recovery mode and the individual anaerobic threshold

The individual anaerobic threshold (IAT) is defined as the highest metabolic rate at which blood lactate (LA) concentrations are maintained at a steady-state during prolonged exercise. The purpose of this study was to compare the effects of active and passive recovery on the determination of IAT following both a submaximal or maximal incremental exercise test. Seven males (VO2max = 57.6 +/- 5.8 ml.kg-1.min -1) did two submaximal, incremental cycle exercise tests (30 W and 4 min per step) and two maximal incremental tests. Blood was sampled repeatedly during exercise and for 12 min during the subsequent recovery period, which was passive for one submaximal and one maximal test and active (approximately 35% VO2max) during the other tests. An IAT metabolic rate and power output were calculated for the submax-passive (IATsp, LA = 1.85 +/- 0.42 mmol.l-1), max-passive (IATmp, LA = 3.41 +/- 1.14 mmol.l-1), submax-active (IATsa, LA = 2.13 +/- 0.45 mmol.l-1) and max-active (IATma, LA = 3.44 +/- 0.73 mmol.l-1) protocols. At weekly intervals, the subjects exercised for 30 min at one of the four IAT metabolic rates. Active recovery did not affect the calculation of IAT, but following the maximal incremental tests, IAT occurred at a higher (p less than 0.05) power output, absolute VO2 and %VO2max (71% VO2max) compared with the IAT determined with the submaximal incremental tests (61% VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)