Creatine feeding does not enhance intramyocellular glycogen concentration during carbohydrate loading: an in vivo study by 31P- and 13C-MRS

The main aim of this study was to examine the hypothesis that creatine (Cr) feedingenhances myocellular glycogen storage in humans undergoing carbohydrateloading. Twenty trained male subjects were randomly assigned to have their dietssupplemented daily with 252 g of glucose polymer (GP) and either 21 g of Cr (CRGP,n=10) or placebo (PL-GP, n=10) for 5 days. Changes in resting myocellularglycogen and phosphocreatine (PCr) were determined with Magnetic ResonanceSpectroscopy (13C- and 31P-MRS, respectively). After CR-GP, the levels of intramyocellularglycogen increased from 147 ± 13 (standard error) mmol·(kg wet weight-1)to 172 ± 13 mmol·(kg wet weight)-1, while it increased from 134 ± 17 mmol·(kg wetweight)- to 182 ± 17 mmol·(kg wet weight)-1 after PL-GP; the increments in intramyocellularglycogen concentrations were not statistically different. The increment inthe PCr/ATP ratio after CR-GP (+ 0.20 ± 0.12) was significantly different comparedto PL-GP (- 0.34 ± 0.16) (p<0.05). The present results do not support the hypothesisthat Cr loading increases muscle glycogen storage (AU)

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Creatine feeding does not enhance intramyocellular glycogen concentration during carbohydrate loading: an in vivo study by 31P- and 13C-MRS.

The main aim of this study was to examine the hypothesis that creatine (Cr) feeding enhances myocellular glycogen storage in humans undergoing carbohydrate loading. Twenty trained male subjects were randomly assigned to have their diets supplemented daily with 252 g of glucose polymer (GP) and either 21 g of Cr (CR-GP, n = 10) or placebo (PL-GP, n = 10) for 5 days. Changes in resting myocellular glycogen and phosphocreatine (PCr) were determined with Magnetic Resonance Spectroscopy (13C- and 31P-MRS, respectively). After CR-GP, the levels of intramyocellular glycogen increased from 147 +/- 13 (standard error) mmol x (kg wet weight(-1)) to 172 +/- 13 m mol x (kg wet weight)(-1), while it increased from 134 +/- 17 mmol x (kg wet weight)(-) to 182 +/- 17 mmol x (kg wet weight)(-1) after PL-GP; the increments in intramyocellular glycogen concentrations were not statistically different. The increment in the PCr/ATP ratio after CR-GP (+ 0.20 +/- 0.12) was significantly different compared to PL-GP (- 0.34 +/- 0.16) (p < 0.05). The present results do not support the hypothesis that Cr loading increases muscle glycogen storage.

Quantitative trait loci for maximal exercise capacity phenotypes and their responses to training in the HERITAGE Family Study.

The purpose of this study was to identify regions of the human genome linked to maximal oxygen uptake (VO2max) and maximal power output (MPO), and their response to a standardized 20-wk endurance-training program in sedentary black and white subjects. A total of 509 polymorphic markers covering the 22 autosomes were used in the genome-wide linkage scan. Baseline phenotypes were adjusted for age, sex, and body mass, whereas the training responses were adjusted for age, sex, and the baseline values. Regression-based single- and multipoint linkage analyses were used. In the sedentary state, a total of 351 and 102 sibling pairs were available for whites and blacks, respectively, and 329 and 90 sibling pairs, respectively, for the training response phenotypes. Baseline VO2max showed promising linkage (P < 0.0023) with 11p15.1 (whites), and suggestive evidence of linkage (0.01 > P > 0.0023) was found on 1p31, 7q32, and 7q36 (blacks). Baseline MPO exhibited promising linkage on 10q23 and suggestive evidence of linkage on 13q33 and 18q11-q12 (whites). VO2max training response yielded promising linkages with markers on 1p31 (blacks) and suggestive on 4q27, 7q34, and 13q12 (whites) and on 16q22 and 20q13.1 (blacks). Training-induced changes in MPO showed promising linkages on 5q23 (whites) and suggestive on 1q21, 4p15.1, and 4p13 (whites) and on 1q22 and 13q11 (blacks). In conclusion, the strongest evidence of linkage was found on chromosomal regions 11p15 and 10q23 for VO2 max and MPO in the sedentary state and on chromosomes 1p31 and 5q23 for their responsiveness to training. These chromosomal regions harbor several candidate genes that deserve further investigation.

Associations between cardiorespiratory responses to exercise and the C34T AMPD1 gene polymorphism in the HERITAGE Family Study.

The associations of the C34T polymorphism of the adenosine monophosphate deaminase 1 (AMPD1) gene with cardiorespiratory phenotypes were tested during cycling exercise at absolute and relative power outputs progressing to exhaustion before and after endurance training for 20 wk in the HERITAGE Family Study cohort (n = 779). Since no blacks were mutant homozygotes (TT), only whites were considered for analysis (400 normal homozygotes, CC; 97 heterozygotes, CT; and 6 TT). For sedentary state, cycling at the absolute power output of 50 W resulted in a higher rating of perceived exertion in TT (P < 0.0001). At the relative intensity of 60% of Vo(2 max), stroke volume was lower in TT (P < 0.05). Maximal values for power output, systolic blood pressure, heart rate, Vco(2), and respiratory exchange ratio were lower in TT (P < 0.05). The cardiorespiratory training response at 50 W and at 60% of Vo(2 max) was similar across C34T-AMPD1 genotypes. However, the maximal values for ventilation, Vo(2), and Vco(2) during exercise increased less in TT (P < 0.01). The results indicate that subjects with the TT genotype at the C34T AMPD1 gene have diminished exercise capacity and cardiorespiratory responses to exercise in the sedentary state. Furthermore, the training response of ventilatory phenotypes during maximal exercise is more limited in TT.

Progressive decrease of intramyocellular accumulation of H+ and Pi in human skeletal muscle during repeated isotonic exercise.

The purpose of this study was to evaluate the hypotheses that accumulation of hydrogen ions and/or inorganic phosphate (Pi) in skeletal muscle increases with repeated bouts of isotonic exercise. (31)P-Magnetic resonance spectroscopy was used to examine the gastrocnemius muscle of seven highly aerobically trained females during four bouts of isotonic plantar flexion. The exercise bouts (EX1-4) of 3 min and 18 s were separated by 3 min and 54 s of complete rest. Muscle ATP did not change during the four bouts. Phosphocreatine (PCr) degradation during EX1 (13.3 +/- 2.4 mmol/kg wet weight) was higher (P < 0.01) compared with EX3-4 (9.7 +/- 1.6 and 9.6 +/- 1.8 mmol/kg wet weight, respectively). The intramyocellular pH at the end of EX1 (6.87 +/- 0.05) was significantly lower (P < 0.001) than those of EX2 (6.97 +/- 0.02), EX3 (7.02 +/- 0.01), and EX4 (7.02 +/- 0.02). Total Pi and diprotonated Pi were significantly higher (P < 0.001) at the end of EX1 (17.3 +/- 2.7 and 7.8 +/- 1.6 mmol/kg wet weight, respectively) compared with the values at the end of EX3 and EX4. The monoprotonated Pi at the end of EX1 (9.5 +/- 1.2 mmol/kg wet weight) was also significantly higher (P < 0.001) than that after EX4 (7.5 +/- 1.1 mmol/kg wet weight). Subjects' rating of perceived exertion increased (P < 0.001) toward exhaustion as the number of exercises progressed (7.1 +/- 0.4, EX1; 8.0 +/- 0.3, EX2; 8.5 +/- 0.3, EX3; and 9.0 +/- 0.4, EX4; scale from 0 to 10). The present results indicate that human muscle fatigue during repeated intense isotonic exercise is not due to progressive depletion of high energy phosphates nor to intracellular accumulation of hydrogen ions, total, mono-, or diprotonated Pi.

Resynthesis of muscle glycogen after soccer specific performance examined by 13C-magnetic resonance spectroscopy in elite players.

The purpose of this study was to examine using 13C-magnetic resonance spectroscopy whether muscle glycogen (Gly) utilized during a simulation of a fatiguing soccer match followed by repeated sprints would be resynthesized during the next 24 h while players consumed their habitual diet. A group of 12 elite young players [mean age 17.5 (SD 0.8) years, mean body mass 68.9 (SD 6.6) kg, mean height 177.0 (SD 5.4) cm] participated in the study. Average muscle Gly content before the simulation was 134 (SD 16) mmol.(kg wet mass)-1 and decreased during the test (P < 0.001) to 80 (SD 29) mmol.(kg wet mass)-1. The value had increased (P < 0.01) to 122 (SD 33) mmol.(kg wet mass)-1 24 h later but it was not significantly different from the value obtained before the soccer test. Dietary analysis of the food intake during the 24 h after the running test revealed that players consumed an average of 2,681 (SD 970) kcal.day-1. Mean daily protein, fat, and carbohydrate (CHO) intakes were 85 (SD 29), 99 (SD 44), and 327 (SD 116) g, respectively. The mean amounts of CHO intake normalised to body mass were 4.8 (SD 1.8) g.(kg body mass)-1. In conclusion, the results of this study showed that despite a CHO intake of less than 5 g.(kg body mass)-1 the habitual diet of soccer players might be sufficient to replenish in 24 h the muscle Gly utilized during soccer specific performance. However, cumulative deficits of about 10% in Gly replenishment as found in the present study might provoke decrements in performance. Thus, players should pay attention to their habitual diets and add more carbohydrates to replenish their daily deficits and perhaps increase their basal levels of intake.

Creatine reduces human muscle PCr and pH decrements and P(i) accumulation during low-intensity exercise.

The purpose of this study was to examine with (31)P-magnetic resonance spectroscopy energy metabolism during repeated plantar flexion isometric exercise (Ex-1-Ex-4) at 32 +/- 1 and 79 +/- 4% of maximal voluntary contraction (MVC) before and during a creatine (Cr) feeding period of 5 g/day for 11 days. Eight trained male subjects participated in the study. ATP was unchanged with Cr supplementation at rest and during exercise at both intensities. Resting muscle phosphocreatine (PCr) increased (P < 0.05) from 18.3 +/- 0.9 (before) to 19.6 +/- 1.0 mmol/kg wet wt after 9 days. At 79% MVC, PCr used, P(i) accumulated, and pH at the end of Ex-1-Ex-4 were similar after 4 and 11 days of Cr supplementation. In contrast, PCr utilization and P(i) accumulation were lower and pH was higher for exercise at 32% MVC with Cr supplementation, suggesting aerobic resynthesis of PCr was more rapid during exercise. These results suggest that elevating muscle Cr enhances oxidative phosphorylation during mild isometric exercise, where it is expected that oxygen delivery matches demands and predominantly slow-twitch motor units are recruited.

Creatine enhances oxygen uptake and performance during alternating intensity exercise.

PURPOSE: The main purpose of the present study was to measure the total oxygen consumed, accumulation of blood metabolites, and performance during alternating intensity exercise before and after a period of creatine (Cr) loading in well-trained humans. METHODS: Fourteen males were randomly assigned to two groups of seven males and were tested before and after 5 d of placebo (PL) or Cr monohydrate (CR) loading (20 g x d(-1)). Oxygen uptake was measured using a breath-by-breath system during bicycle exercise alternating every 3 min between bouts at 30%(-30%) and 90% (-90%) of the maximal power output to exhaustion. Blood samples were also obtained at rest, before the end of each cycling load, at exhaustion, and 5-min postexercise. RESULTS: The oxygen consumed during 1-90% (5.08 +/- 0.39 L) and 2-90% (5.32 +/- 0.30 L) was larger after CR (5.67 +/- 0.34 and 5.78 +/- 0.35 L, P < 0.01 and P < 0.05, respectively). Blood ammonia accumulation at the end of 1-90% (23.1 +/- 6.5 micromol x L(-1)) and 3-30% (64.7 +/- 15.2 micromol x L(-1)) was lower after CR (P < 0.05), whereas plasma uric acid accumulation was lower at exhaustion (P < 0.05) and 5-min postexercise (P < 0.01). Time to exhaustion increased (P < 0.05) from 29.9 +/- 3.8 to 36.5 +/- 5.7 min after CR, whereas it remained the same after PL. CONCLUSIONS: The results indicate that Cr feeding increases the capacity of human muscle to perform work during alternating intensity contraction, possibly as a consequence of increased aerobic phosphorylation and flux through the creatine kinase system.

In vivo evaluation of the effects of continuous exercise on skeletal muscle triglycerides in trained humans.

Magnetic resonance spectroscopy (1H MRS) and imaging (MRI) were used to investigate the effects of a bout of moderate prolonged exercise on intra (IMCL)- and extramyocellular lipid (EMCL) utilization in the soleus, tibialis anterior, and gastrocnemius muscles of five trained human subjects. MRI and 1H MRS measurements were obtained before and after a 90 min run on a calibrated treadmill at a velocity corresponding to 64 +/- 1.5% of each subjects' maximal rate of oxygen consumption. There were significant decreases in IMCL following exercise in the tibialis (pre: 22.37 +/- 4.33 vs. post: 15.16 +/- 3.25 mmol/kg dry wt; P < 0.01) and soleus (pre: 36.93 +/- 1.45 vs. post: 29.85 +/- 2.44 mmol/kg dry wt; P < 0.01) muscles. There was also a decrease in the gastrocnemius muscle, although this did not reach the level of significance (pre: 33.78 +/- 5.35 vs. post: 28.48 +/- 5.44 mmol/kg dry weight; P < 0.10). No significant changes were observed in EMCL or subcutaneous fat. In conclusion, this study showed that IMCL were significantly utilized in the tibialis and soleus muscles of aerobically endurance-trained humans. The absence of significant utilization of IMCL in the gastrocnemius may reflect differences in fiber type and/or intensity of contraction for each muscle group.

Diversity in levels of intracellular total creatine and triglycerides in human skeletal muscles observed by (1)H-MRS.

We used (1)H-magnetic resonance spectroscopy to noninvasively determine total creatine (TCr), choline-containing compounds (Cho), and intracellular (IT) and extracellular (between-muscle fibers) triglycerides (ET) in three human skeletal muscles. Subjects' (n = 15 men) TCr concentrations in soleus [Sol; 100.2 +/- 8.3 (SE) mmol/kg dry wt] were lower (P < 0.05) than those in gastrocnemius (Gast; 125.3 +/- 9.2 mmol/kg dry wt) and tibialis anterior (TA; 123. 7 +/- 8.8 mmol/kg dry wt). The Cho levels in Sol (35.8 +/- 3.6 mmol/kg dry wt) and Gast (28.5 +/- 3.5 mmol/kg dry wt) were higher (P < 0.001 and P < 0.01, respectively) compared with TA (13.6 +/- 2. 4 mmol/kg dry wt). The IT values were found to be 44.8 +/- 4.6 and 36.5 +/- 4.2 mmol/kg dry wt in Sol and Gast, respectively. The IT values of TA (24.5 +/- 4.5 mmol/kg dry wt) were lower than those of Sol (P < 0.01) and Gast (P < 0.05). There were no differences in ET [116.0 +/- 11.2 (Sol), 119.1 +/- 18.5 (Gast), and 91.4 +/- 19.2 mmol/kg dry wt (TA)]. It is proposed that the differences in metabolite levels may be due to the differences in fiber-type composition and deposition of metabolites due to the adaptation of different muscles during locomotion.

Noninvasive measurement of muscle high-energy phosphates and glycogen concentrations in elite soccer players by 31P- and 13C-MRS.

PURPOSE: The purpose of this study was to measure noninvasively the absolute concentrations of muscle adenosine triphosphate [ATP], phosphocreatine [PCr], inorganic phosphate (Pi), and glycogen [Gly] of elite soccer players. METHODS: Magnetic resonance spectroscopy (31P- and 13C-MRS) was used to measure the concentrations of metabolites in the calf muscles of 18 young male players [age = 17.5 +/- 1.0 (SD) yr]. RESULTS: Average muscle [PCr] and [ATP] were 17.8 +/- 3.3 and 6.0 +/- 1.2 mmol x (kg wet weight)(-1), respectively. The ratios of Pi/PCr and PCr/ATP were 0.15 +/- 0.05 and 3.00 +/- 0.26, respectively. The muscle [Gly] was 144 +/- 54 mmol x (kg wet weight)(-1). There was a high correlation (r = 0.93, P < 0.0001) between muscle ATP and PCr concentrations, but there was no correlation between [Gly] and [PCr] or [ATP]. The concentrations of the different metabolites determined in the present study with noninvasive MRS methods were within the ranges of values reported in human muscle from biochemical analysis of muscle biopsies. CONCLUSION: MRS methods can be utilized to assess noninvasively the muscle energetic status of elite soccer players during a soccer season. The high correlation between ATP and PCr might be indicative of fiber type differences in the content of these two metabolites.

Muscle glycogen degradation during simulation of a fatiguing soccer match in elite soccer players examined noninvasively by 13C-MRS.

PURPOSE: The purpose of this research project was to noninvasively determine individual muscle glycogen [Gly] degradation during a test intended to predict individual fatigue in intense soccer matches. METHODS: The [Gly] of the calf muscles of 17 elite soccer players [age = 17.4 +/- 0.8 (SD)] were measured with 13C-MRS before and after an alternating velocity test to exhaustion. Blood samples were taken before and 3 min after the test for determination of blood metabolites. RESULTS: Average muscle [Gly] was 135 +/- 53 mmol x (kg wet weight)(-1) before and 87 +/- 27 mmol x (kg wet weight)(-1) (P < 0.001) after exhaustion (42 +/- 25 min). There was a high correlation (r = 0.87, P < 0.0001) between muscle [Gly] at rest and net muscle [Gly] utilized. There was also a more moderate correlation (r = 0.62, P < 0.01) between net muscle [Gly] used and time to exhaustion during the soccer-specific test. There was some evidence of correlation (r = 0.42, P = 0.09) between resting [Gly] and time to exhaustion. Plasma lactate increased (P < 0.001) from 0.8 +/- 0.4 before the test to 2.5 +/- 1.0 mmol x L(-1) at exhaustion, whereas ammonia was raised (P < 0.0001) from 44.1 +/- 10.3 to 89.7 +/- 14.9 micromol x L(-1). Similarly, plasma free fatty acids were elevated (P < 0.0001) from 148 +/- 106 to 797 +/- 401 micromol x L(-1), and glycerol was increased (P < 0.0001) from 48.3 +/- 17.7 to 182.2 +/- 61.8 micromol x L(-1). Insulin levels (11.9 +/- 3.7 vs 11.7 +/- 4.8 microU x mL(-1)) remained the same. Creatine kinase levels increased (P < 0.0001) from 486 +/- 501 to 640 +/- 548 micromol x L(-1) after the test. CONCLUSIONS: We conclude that exhaustion during soccer-specific performance is related to the capacity to utilize muscle [Gly]. The results underline the importance of dietary counseling (glycogen loading and resynthesis strategies) and proper training to enhance the glycogen levels and glycogenolytic capacity of the players.

Dietary and performance assessment of elite soccer players during a period of intense training.

This study examined the nutritional and performance status of elite soccer players during intense training. Eight male players (age 17+/-2 years) of the Puerto Rican Olympic Team recorded daily activities and food intake over 12 days. Daily energy expenditure was 3,833+/-571 (SD) kcal, and energy intake was 3,952+/-1,071 kcal, of which 53.2+/-6.2% (8.3 g x kg BW(-1)) was from carbohydrates (CHO), 32.4+/-4.0% from fat, and 14.4+/-2.3% from protein. With the exception of calcium, all micronutrients examined were in accordance with dietary guidelines. Body fat was 7.6+/-1.1% of body weight. Time to completion of three runs of the soccer-specific test was 37.65+/-0.62 s, and peak torques of the knee flexors and extensors at 60 degrees x s(-1) were 139+/-6 and 225+/-9 N x m, respectively. Players' absolute amounts of CHO seemed to be above the minimum recommended intake to maximize glycogen storage, but calcium intakes were below recommended. Their body fat was unremarkable, and they had a comparatively good capacity to endure repeated bouts of intense soccer-specific exercise and to exert force with their knee extensors and flexors.

Intracellular and extracellular skeletal muscle triglyceride metabolism during alternating intensity exercise in humans.

1. The main purpose of this study was to evaluate non-invasively with magnetic resonance spectroscopy (1H-MRS) changes in the concentrations of intracellular (IT) and extracellular (between muscle fibres) triglycerides (ET) in skeletal muscles of trained males (age range: 24-38 years) during two standard exercise protocols of alternating velocities. 2. Protocol 1 consisted of locomotion in a shuttle manner between two lines 30 m apart at four different velocities (1, 2, 3, and 4 m s-1) which were alternated every minute in a standard routine for 90 min, whereas Protocol 2 included locomotion between two lines 20 m apart at only three velocities (2, 2.7 and 4 m s-1) until volitional exhaustion. The heart rate during both protocols fluctuated between 140 and 200 beats min-1. 3. Using pre-exercise muscle water to quantify individual total creatine (TCr) that was utilized as an internal standard and assuming that TCr does not change during exercise, subjects' mean IT and ET concentrations in soleus (Sol) muscle before Protocol 1 (n = 8) were 45.8 +/- 4.8 mmol (kg dry weight)-1 (mean +/- S.E.M.) and 93.1 +/- 14.1 mmol (kg dry weight)-1, respectively. After the exercise, the concentrations of IT and ET were not significantly different from the values at rest. Before Protocol 2 (n = 4), IT concentrations in Sol, gastrocnemius (Gast) and tibialis (Tib) muscles were 46.4 +/- 13.6, 35.0 +/- 12.1 and 23.1 +/- 4.8 mmol (kg dry weight)-1, respectively, and were not affected by the exhaustive exercise. The ET concentrations in Sol, Gast and Tib were 136.4 +/- 38.1, 175.3 +/- 86.5 and 79.3 +/- 20.0 mmol (kg dry weight)-1 respectively, and they did not change significantly after exhaustion. 4. The study showed that levels of IT and ET were not affected by alternating intensity exercise to fatigue. This suggests that IT and ET in human Sol, Gast and Tib muscles do not contribute significantly to the energy turnover during this type of exercise. Energy for this type of muscle contraction may arise primarily from muscle phosphocreatine (PCr) and glycogen breakdown, circulating glucose and fatty acids from triglycerides other than those encountered within and between muscle cells.

Body composition and nutritional assessments in soccer.

This review summarizes results from studies investigating the physical characteristics, daily energy expenditures, diets, and effects of nutritional supplements to the habitual diets of soccer players. The results show that players fall within a wide range of stature and body weight, and they are classified as mesomorphs. The body fat of male players is about 10% of body weight, whereas the average for females is about 21%. Energy expenditure for males is about 4,000 kcal on training days and 3,800 kcal on match day, while energy intake reported in other studies is on the order of 3,700 kcal. Carbohydrate (CHO), fat, and protein intakes are about 53, 30, and 14% of energy intake, respectively, the remaining being from alcohol intake. There are indications that CHO supplements might be beneficial during soccer performance. However, more research is needed to clarify the importance of branched-chain amino acid and creatine supplementation in soccer.

Oxidative metabolism and anaerobic glycolysis during repeated exercise.

The purpose of the present study was to examine aerobic and muscle anaerobic energy production during supramaximal repeated exercise. Eight subjects performed three 2-min bouts of cycling (EX1-EX3) at an intensity corresponding to about 125 % of VO2 max separated by 15 min of rest. Ventilatory variables were measured breath by breath during the exercise and a muscle biopsy was taken before and after each exercise bout. Blood samples were collected before and after each cycling period and during the recovery periods. Total work in the first 2 min bout of cycling, EX1, [46.3 +/- 2.1 KJ] was greater than in the second, EX2, (p < 0.01) and in the third, EX3, (p < 0.05). The ATP utilization [4.0 +/- 1.4 mmol x (kg dry weight)(-1), EX1] during the three exercise bouts was the same. The decrement in muscle phosphocreatine (PCr) [46.8 +/- 8.5 mmol x (kg dry weight)(-1), EX1] was also similar for the three exercise bouts. Muscle lactate accumulation was greater (p < 0.05) during EX1 compared to EX2 and EX3. The total oxygen consumption was the same for the three exercise bouts, but when it is corrected for the total work performed, oxygen uptake during EX2 (153 +/- 9 ml x KJ(-1)) and EX3 (150 +/- 9 ml x KJ(-1)) was higher (p < 0.01 and p < 0.05, respectively) than during EX1 (139 +/- 8 ml x KJ(-1)). The present data suggest that oxidative metabolism does not compensate for the reduction of anaerobic glycolysis during repeated fatiguing exercise.

Effects of hyperhydration on total body water, temperature regulation and performance of elite young soccer players in a warm climate.

The purpose of this study was to test the effect of increased fluid intake on temperature regulation and performance in elite soccer players. Eight players of the Puerto Rico National Team were studied under field conditions at a Wet Bulb Globe Temperature (WBGT) heat stress index of 25.3 +/- 0.5 degrees C. They were young (17.0 +/- 0.6 yr) and well aerobically conditioned, as shown by their maximum aerobic power of 69.2 +/- 0.7 ml.kg(-1).min(-1). Players were randomly allocated to a week of voluntary hydration (VH) (fluid intake = 2.7 +/- 0.2.day(-1)) and a week of hyperhydration (HH) (fluid intake = 4.6 +/- 0.2.day(-1)) (p <0.05) prior to a soccer match. Their total body water (TBW) increased in HH compared to VH (p<0.05), despite a significant increase in urine output (p < 0.01). The soccer match was played at 82 +/- 7% (VH) and 83 +/- 6% (HH) of maximum heart rate. Sweat losses and core temperature increases during the match were similar in both hydration conditions. When the environmental conditions were taken into consideration, the increase in core temperature during the match rose, as a function of the heat stress index, only in VH (p < 0.05). Plasma volume was slightly reduced in both hydration conditions (ns). Performance assessment at the end of the soccer match revealed that average time to complete 7 repetitions of a soccer specific test was significantly increased (p < 0.05) after the match in both hydration conditions but showed no difference between them. Peak torque and fatigability of knee flexor and extensor muscle groups at 240 deg.sec(-1), measured on a Cybex 340 dynamometer were similar in both hydration conditions and not affected by the soccer match. The data suggest that additional water intake in these heat-acclimated players increased body water reserves and improved temperature regulation during a soccer match with no significant effect on the decrement in soccer specific performance observed at the end of a soccer match.