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.     

Effects of precooling on thermoregulation during subsequent exercise

PURPOSE: The purpose of this study was to examine the effect of a decreased body core temperature before a simulated portion of a triathlon (swim,15 min; bike, 45 min) and examine whether precooling could attenuate thermal strain and increase subjective exercise tolerance in a warm environment (26.6 degrees C/60% relative humidity (rh)). METHODS: Six endurance trained triathletes (28+/-2 yr, 8.2+/-1.7% body fat) completed two randomly assigned trials 1 wk apart. The precooling trial (PC) involved lowering body core temperature (-0.5 degrees C rectal temperature, Tre) in water before swimming. The control trial (CON) was identical except no precooling was performed. Water temperature and environmental conditions were maintained at 25.6 degrees C and 26.6 degrees C/60% rh, respectively, throughout all testing. RESULTS: Mean time to precool was 31+/-8 min and average time to reach baseline Tre during cycling was 9+/-7 min. Oxygen uptake (VO2), HR, skin temperature (Tsk), Tre, RPE, and thermal sensation (TS) were recorded following the swim segment and throughout cycling. No significant differences in mean body (Tb) or Tsk were noted between PC and CON, but a significant difference (P < 0.05) in Tre between treatments was noted through the early phases of cycling. No significant differences were reported in HR, VO2, RPE, TS, or sweat rate (SR) between treatments. Body heat storage (S) was negative following swimming in both PC (-92+/-6 W x m2) and CON (-66+/-9 W x m2). A greater S occurred in PC (109+/-6 W x m2) vs CON (79+/-4 W x m2) during cycling (P < 0.05). CONCLUSIONS: Precooling attenuated the rise in Tre, but this effect was transient. Therefore, precooling is not recommended before a triathlon under similar environmental conditions.     

Effects of acute ingestion of salbutamol during submaximal exercise

To assess the eventual effects of acute oral salbutamol intake on performance and metabolism during submaximal exercise, nine healthy volunteers completed two cycling trials at a power corresponding to 80-85% VO2max, after either placebo (Pla) or salbutamol (Sal, 6 mg) treatment, according to a double-blind randomized protocol. Blood samples were collected both at rest and during exercise (5 min-, 10 min-, 15 min-exhaustion) for C-peptide, FFA, lactate and blood glucose measurements. Cycling performance was significantly improved in the Sal vs. Pla trials (p < 0.05). After Sal intake, resting C-peptide, lactate, FFA and blood glucose values were higher whereas exercise lactate and free fatty acid concentrations were greater during and at the conclusion of the exercise period (p < 0.05). These results suggest that acute salbutamol ingestion improved performance during submaximal exercise probably through an enhancement of the overall contribution to energy production from both aerobic and anaerobic metabolisms.     

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.     

Effects of acute prednisolone intake on substrate utilization during submaximal exercise

We examined the hypothesis that acute therapeutic glucocorticoid intake could change the contribution of fat and carbohydrate (CHO) in energy production during exercise. Nine healthy recreationally-trained male subjects twice performed submaximal exercise (60 min at 60 % VO2max) after ingestion of placebo (Pla) or 20 mg of prednisolone (Pred), according to a double blind and randomized protocol. Respiratory exchange was monitored during exercise and blood samples were collected at rest, every 10 min during exercise and after 5, 10, and 20 min of passive recovery. Pred intake significantly increased total energy expenditure during exercise, but CHO oxidation was lower and fat oxidation higher after Pred vs. Pla. ACTH and IL-6 concentrations were significantly decreased with Pred during exercise, whereas no variations were found in GH, insulin, blood glucose, and lactate between the 2 treatments. In conclusion, it appears that acute prednisolone systemic administration does reduce total carbohydrate oxidation during submaximal exercise. Further studies are necessary to clarify the mechanisms involved and to determine whether this modification in the substrate oxidation balance under glucocorticoid administration in recreationally-trained male subjects could result in a competitive advantage in elite athletes.     

Effects of reduced ambient temperature on fat utilization during submaximal exercise

PURPOSE: The influence of cold air exposure on fuel utilization during prolonged cycle exercise was investigated. METHODS: Nine male subjects cycled for 90 min in ambient temperatures of -10 degrees C, 0 degrees C, 10 degrees C, and 20 degrees C. External work performed between conditions was constant. Mean oxygen consumption (VO2) over the 90 min in the 20 degrees C trial corresponded to 64 +/- 5.8% VO2peak. RESULTS: Although mean skin temperature was different between trials (P < 0.05), rectal temperatures were not different. At -10 degrees C and 0 degrees C, the respiratory exchange ratio was higher compared with 10 degrees C and 20 degrees C (0.98 +/- 0.01 and 0.97 +/- 0.01 vs 0.92 +/- 0.01 and 0.91 +/- 0.01; P < 0.05). The associated rates of fat oxidation were lower at -10 degrees C and 0 degrees C compared with 10 degrees C and 20 degrees C (0.15 +/- 0.06 and 0.17 +/- 0.06 vs 0.35 +/- 0.06 and 0.40 +/- 0.04 g.min-1; P < 0.05). Blood glycerol was lower at -10 degrees C and 0 degrees C compared with 20 degrees C (P < 0.05); mean values were 0.13 +/- 0.0, 0.13 +/- 0.0, and 0.18 +/- 0.0 mmol.L-1 for the -10 degrees C, 0 degrees C, and 20 degrees C trials, respectively. Mean VO2 was lower in the -10 degrees C trial than the 20 degrees C trial (2.53 +/- 0.06 vs 2.77 +/- 0.09. L.min-1; P < 0.05). Mean blood glucose concentrations were lower at -10 degrees C than 20 degrees C (4.9 +/- 0.2 vs 5.3 +/- 0.1 mmol.L-1; P < 0.05). Although plasma epinephrine concentrations were greater during the 20 degrees C trial compared with all other trials (P < 0.05), plasma norepinephrine did not differ between trials. CONCLUSION: The diminished fat oxidation at colder temperatures potentially reflects a reduction in lipolysis and/or mobilization of FFA or impairment in the oxidative capacity of the muscle.     

Effects of gender on physiological responses during submaximal exercise and recovery

PURPOSE: This investigation was conducted to compare the physiological responses of men and women, both during and following an exercise bout at the same relative submaximal intensity. METHODS: Ten untrained men (20.7+/-0.5 yr, 178.4+/-2.3 cm, 79.6+/-4.8 kg; mean+/-SE) and 10 untrained women (20.3+/-0.3 yr, 163.8+/-2.2 cm, 59.5+/-2.1 kg) cycled for 30 min at 60-65% of their predetermined peak oxygen uptake. Physiological variables were measured before exercise, at 15 and 30 min of exercise, and at 5 and 15 min postexercise. For each variable of interest, a two-way repeated-measures of analysis was used to assess the main effects of gender and time, along with potential interactive effects. RESULTS: Our data revealed that for many variables including HR, relative HR (% peak value), mean arterial pressure, and rectal temperature, men and women responded similarly both during exercise and throughout the recovery period. In contrast, significant (P相似文献   

Effects of submaximal exercise on high-density lipoprotein-cholesterol subfractions

Acute high-density lipoprotein-cholesterol (HDL) changes were determined in 18 healthy college aged-men completing two-counterbalanced running trials at different exercise intensities: trial 1 at 70 % lactate threshold (LT) (372.5 +/- 28.9 kcal); trial 2 at LT intensity (365.9 +/- 75.9 kcal). For each trial, blood samples were collected at pre-exercise (baseline), 15 min post-exercise (15 m PE) and 24 hours post-exercise (24 h). Serum samples were analyzed for HDL/HDL 2 /HDL 3 subfraction, low density lipoprotein (LDL), very low density lipoprotein (VLDL), total cholesterol (TC), free cholesterol (FC), cholesterol ester, and triglycerides (TG). In addition, capillary blood samples were collected for analysis of blood lactate concentrations during incremental test to determine LT. All samples were corrected for plasma volume changes and compared to pre-exercise (baseline). In assessing the lipid and lipoprotein variables, the significant increase in HDL (p < 0.05) at the 24 h was due to the increase in both HDL 2 and HDL 3. The increase in 15 m PE TC at the LT intensity occurred while the decreases in 24 h TG and VLDL concentrations at the LT intensity occurred at different time periods, respectively. These decreases in the concentrations of TG and VLDL were significantly different, contributing to change in 24 h HDL concentration. No significant difference was determined in changes of HDL over time ratios of FC/CE and HDL 2 /HDL 3. Therefore, the significant increase in 24 h HDL at LT intensity was potentially due to increases in both HDL 2 and HDL 3 subfractions even though 24 h FC was increased significantly. Exercise at LT intensity might favourably alter the lipid profile as demonstrated in 24 h HDL concentration in combination with decreases in TG and VLDL at 24 h post-exercise. Consequently, the LT intensity might appear to be the threshold intensity of acute aerobic exercise (expending 350 kcal) necessary to promote a significant increase in HDL.     

Effects of prior strength exercise on the heart rate oxygen uptake relationship during submaximal exercise.

Fourteen young males (mean age 26.7 yrs) were tested to determine if there was an alteration, in the heart rate-oxygen uptake relationship during submaximal cycle ergometer exercise following isokinetic strength training activity as has been documented following high intensity endurance activity. Results indicated that there was a significant increase rate without a concomitant increase in heart oxygen uptake during the first five minutes of submaximal cycle riding at 73% VO2max after heavy strength leg exercise, angular velocity of 30 degrees/second, when compared to no prior exercise. This alteration in the heart rate-oxygen uptake relation is not apparent by 20 minutes of the same submaximal exercise despite higher lactate values and greater ratings of perceived exertion. For individuals using heart rate as a guide to exercise intensity, the elevated heart rate at five minutes of submaximal exercise following heavy strength leg exercise does not exceed the 20 minute value which is an accurate reflection of energy cost and intensity.     

Effects of acute and chronic metoprolol administration during submaximal and maximal exercise

The effects of different dosages of the beta 1-adrenoceptor blocker metoprolol and of acute and chronic administration of this beta-blocker during physical exercise were compared in healthy normotensive subjects. Placebo, 0.15 mg/kg, and 0.30 mg/kg metoprolol were administered intravenously 10 min before a progressive bicycle ergometer test up to exhaustion. Thereafter, subjects were treated for 4 weeks with placebo or slow-release metoprolol (1 X 200 mg/day). At the end of each 4th week of treatment, a maximal exercise test was performed. Heart rate, ventilation, oxygen consumption, and plasma concentrations of free fatty acids, glucose, and lactate were determined at rest and during exercise. After the low (0.15 mg/kg) i.v. dose, the heart rate during maximal exercise was reduced from 189 +/- 2 to 155 +/- 2 bts/min (P less than 0.001). This reduction was significantly smaller than that after the high (0.30 mg/kg) i.v. dose (177 +/- 3 to 137 +/- 4 bts/min, P less than 0.001) and during chronic treatment (176 +/- 3 to 132 +/- 2 bts/min, P less than 0.001). The difference between the high i.v. dose and chronic treatment was not significant. After the low i.v. dose, the heart rate was the only variable affected. After the high i.v. dose, the heart rate, exercise time, maximal oxygen uptake, and plasma glucose and free fatty acid concentration during maximal exercise were reduced, and maximal lactate concentration tended to be lower. During submaximal exercise, no significant differences between placebo or beta-blocker administration were found, except for heart rate, which was reduced after beta-blockade.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of specific warm-up at various intensities on energy metabolism during subsequent exercise

BACKGROUND: To investigate the effects of specific warm-up at various intensities on energy metabolism during subsequent intense exercise. METHODS: Experimental design: specific warm-up was consisted of 3 sets of wrist flexions for 5 min, with each set followed by a 3-min rest. The intensity of specific warm-up was set at 20%, 30% or 40% of maximal voluntary contraction (MVC). The subjects then performed a set of wrist flexions at 60% MVC for 4 min as the criterion exercise. For the control experiment, criterion exercise was done without specific warm-up. Participants: Five healthy volunteers. Measurements: using phosphorus-31 magnetic resonance spectroscopy, spectra were obtained from the wrist flexor muscles to determine the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) and intracellular pH. RESULTS: The Pi/PCr during the criterion exercise after specific warm-up at any intensity was not significantly different from that without specific warm-up. The intracellular pH during the criterion exercise after specific warm-up at 30% or 40% MVC was significantly higher than that without specific warm-up. CONCLUSIONS: These results indicate that mild warm-up exercise could inhibit the development of intracellular acidosis during subsequent intense exercise.     

The effects of speech production on physiologic responses during submaximal exercise

PURPOSE: To investigate the effects of speech production on physiological responses during sub maximal exercise of various intensities. METHODS: Three constant levels running at work intensities corresponding to 65%, 75%, and 85% of the subjects' (N = 14) VO(2) max were performed with and without talking. These loads were chosen to represent the range of training intensities, which are most often used by the general population for improving cardiovascular fitness. During both sessions, various cardiopulmonary variables were measured breath-by-breath. RESULTS: Oxygen uptake, ventilation, breathing frequency, CO(2) production, total respiration cycle time, and expiration time decreased significantly while blood lactate, blood pressure, and end tidal CO(2) increased. There were no significant differences between talking and being silent in heart rate, inspiration time, and in tidal volume. CONCLUSIONS: Speech production during sub maximal exercise results in a significant reduction in minute ventilation and oxygen uptake with an accompanying elevation of lactic acid and blood pressure. These findings are of particular relevance for planning rehabilitation or training programs for ill as well as for healthy populations.     

Influence of training on NIRS muscle oxygen saturation during submaximal exercise

PURPOSE: Endurance training improves the oxygen delivery and muscle metabolism. Muscle oxygen saturation measured by near infrared spectroscopy (IR-SO(2)), which is primarily influenced by the local delivery/demand balance, should thus be modified by training. We examined this effect by determining the influence of change in blood lactate and muscle capillary density with training on IR-SO(2) in seven healthy young subjects. METHODS: Two submaximal exercise tests at 50% (Ex1) and 80% pretraining VO(2max) (Ex2) were performed before and after a 4-wk endurance-training program. RESULTS: VO(2max) increased only slightly (+8%, NS) with training but the training effect was confirmed by the increased capillary density (+31%, P < 0.01) and citrate synthase activity (50%, P < 0.01), determined from muscle biopsy samples. Before training, blood lactate increased during the first 5 min of Ex1 and then remained constant (3.8 +/- 0.5 mmol x L(-1), P < 0.01), whereas it increased continuously during Ex2 (8.9 +/- 1.8 mmol x L(-1), P < 0.001). After training, lactate decreased significantly and remained constant during the two bouts of exercise (2.0 +/- 0.4 and 3.7 +/- 1.2 at the end of Ex1 and Ex2, respectively, both P < 0.001). During Ex1, IR-SO(2) dropped initially at the onset of exercise and recovered progressively without reaching the resting level. Training did not change this pattern of IR-SO(2). During Ex2, IR-SO(2) decreased progressively during the 15 min of exercise (P < 0.05); IR-SO2 kept constant after the initial drop after training. We found a significant relationship (r = 0.42, P = 0.03) between blood lactate and IR-SO(2) at the end of both bouts of exercise; this relationship was closer before training. By contrast, IR-SO(2) or IR-BV was not related to the capillary density. CONCLUSION: The training-induced adaptation in blood lactate influences IR-SO(2) during mild- to hard-intensity exercise. Thus, NIRS could be used as a noninvasive monitoring of training-induced adaptations.     

Fat and carbohydrate metabolism during submaximal exercise in children

During exercise, the contribution of fat and carbohydrate to energy expenditure is largely modulated by the intensity of exercise. Age, a short- or long-term diet enriched in carbohydrate or fat substrate stores, training and gender are other factors that have also been found to affect this balance. These factors have been extensively studied in adults from the perspective of improving performance in athletes, or from a health perspective in people with diseases. During the last decade, lifestyle changes associated with high-energy diets rich in lipid and reduced physical activity have contributed to the increase in childhood obesity. This lifestyle change has emerged as a serious health problem favouring the early development of cardiovascular diseases, insulin resistance or type 2 diabetes mellitus. Increasing physical activity levels in young people is important to increase energy expenditure and promote muscle oxidative capacity. Therefore, it is surprising that the regulation of balance between carbohydrate and lipid use during exercise has received much less attention in children than in adults. In this review, we have focused on the factors that affect carbohydrate and lipid metabolism during exercise and have identified areas that may be relevant in explaining the higher contribution of lipid to energy expenditure in children when compared with adults. Low muscle glycogen content is possibly associated with a low activity of glycolytic enzymes and high oxidative capacity, while lower levels of sympathoadrenal hormones are likely to favour lipid metabolism in children. Changes in energetic metabolism occurring during adolescence are also dependent on pubertal events with an increase in testosterone in boys and estrogen and progesterone in girls. The profound effects of ovarian hormones on carbohydrate and fat metabolism along with their effects on oxidative enzymes could explain that differences in substrate metabolism have not always been observed between girls and women. Finally, although the regulatory mechanisms of fat and carbohydrate balance during exercise are quite well identified, there are a lack of data specific to children and most of the evidences reported in this review were drawn from studies in adults. Isotope tracer techniques and nuclear magnetic resonance will allow non-invasive investigation of the metabolism of the different substrate sources in skeletal muscle.     

Pre-exercise food and heart rate during submaximal exercise.

The heart rates of 20 movement studies students were measured during multi-stage cycle ergometer tests. The tests were repeated on five occasions following the ingestion of different pre-exercise meals and the results compared. A glucose solution taken three hours prior to the exercise (G3) resulted in the lowest heart rates at each work rate. The highest heart rates at each work rate were recorded following the ingestion of glucose or protein one hour before the exercise (G1 and P1 respectively). The heart rate values during G3 were on average 10.3 beat.min-1 lower than those used during G1 and P1. Intermediate heart rates were obtained with protein taken three hours prior to the exercise or a complete fast for 12 to 14 hours. The results have implications for those attempting to predict maximum oxygen uptake from submaximal heart rates.     

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.