Sleep architecture of elite soccer players surrounding match days as measured by WHOOP straps.

This study aimed to quantify and compare sleep architecture before and after home and away matches in elite soccer players from the English Premier League. Across two seasons, 6 male players (age 28 ± 5 y; body mass 85.1 ± 9.5 kg; height 1.86 ± 0.09 m) wore WHOOP straps to monitor sleep across 13 matches that kicked off before 17:00 h. For each, sleep was recorded the night before (MD-1), after (MD) and following the match (MD +1). Across these 3 days total sleep time (TST), sleep efficiency (SE), sleep disturbances, wake time, light sleep, deep sleep, REM sleep, sleep and wake onsets, alongside external load, were compared. TST was reduced after MD versus MD +1 (392.9 ± 76.4 vs 459.1 ± 66.7 min, p = 0.003) but no differences existed in any other sleep variables between days (p > 0.05). TST did not differ after home (386.9 ± 75.7 min) vs. away matches (401.0 ± 78.3 min) (p = 0.475), nor did other sleep variables (p > 0.05). GPS-derived external load peaked on MD (p < 0.05). In conclusion, despite reduced TST on MD, sleep architecture was unaffected after matches played before 17:00 h, suggesting sleep quality was not significantly compromised.

Fluid Balance and Carbohydrate Intake of Elite Female Soccer Players during Training and Competition.

This study examined sweat rate, sweat sodium concentration [Na+], and ad-libitum carbohydrate and fluid intakes in elite female soccer players during training (n = 19) and a match (n = 8); eight completed both for comparisons. Body mass (kg) was obtained before and after exercise to calculate sweat rate. The sweat [Na+] was determined from absorbent patches on the thigh or back. Sweat rate, percentage body mass change, and sweat [Na+] for 19 players during training were 0.47 ± 0.19 L·h-1, +0.19 ± 0.65%, and 28 ± 10 mmol·L-1, respectively. Sweat rate was higher during a match (0.98 ± 0.34 L·h-1) versus training (0.49 ± 0.26 L·h-1, p = 0.007). Body mass losses were greater post-match (-1.12 ± 0.86%) than training (+0.29 ± 0.34%, p = 0.003). Sweat [Na+] was similar for training (29 ± 9 mmol·L-1) and a match (35 ± 9 mmol·L-1) (p = 0.215). There were no differences in match versus training carbohydrate intakes (2.0 ± 2.3 g·h-1, 0.9 ± 1.5 g·h-1, respectively, p = 0.219) or fluid intakes (0.71 ± 0.30 L·h-1, 0.53 ± 0.21 L·h-1, respectively, p = 0.114). In conclusion, female soccer players' sweat rates were higher during a match than during training, and carbohydrate intakes were below recommendations for matches and training.

Self-reported current sleep behaviors of adult athletes from different competitive levels and sports.

OBJECTIVES: To quantify self-reported current sleep behaviors in a range of adult athletes. In addition, to determine any differences in sleep duration and sleep quality, depending on sport type and competitive level. MATERIAL AND METHODS: In this cross-sectional study, 313 athletes (243 male, 70 female), competing in a variety of sports and competitive level, completed the Pittsburgh sleep quality index (PSQI) and a questionnaire which captured current sleep behaviors. Sleep quality was calculated using the global PSQI score (≥ 5 indicative of poor sleep quality). RESULTS: On average, athletes self-reported sleep duration was 7:34 ± 1:00 h:min. Overall, 19% of athletes achieved less than 7 h of sleep, 50% achieved less than 8 h. Global PSQI score was 5.0 ± 2.4, with poor sleep quality found in 55% of athletes. Sleep duration was significantly shorter in runners compared to basketball, soccer and rugby players (p < 0.05). Recreational athletes slept significantly less (7:08 ± 0:54 h:min) than competitive (7:32 ± 1:00 h:min), national (7:50 ± 1:00 h:min) and elite level athletes (7:49 ± 0:51 h:min). No differences in sleep quality were found between sport or competitive level. DISCUSSION: Half of the athletes failed to achieve 8 h of sleep per night and the majority reported compromised sleep quality. Sport type and competitive level may influence sleep duration; however, these factors do not seem to cause discrepancies in sleep quality. This study provides novel data into the sleep behaviors of adult athletes, and suggests strategies to improve sleep duration and quality may be warranted.

Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners.

AIM: The purpose of this study was to evaluate hydration status, fluid intake, sweat rate, and sweat sodium concentration in recreational tropical native runners. METHODS: A total of 102 males and 64 females participated in this study. Participants ran at their self-selected pace for 30-100 min. Age, environmental conditions, running profiles, sweat rates, and sweat sodium data were recorded. Differences in age, running duration, distance and pace, and physiological changes between sexes were analysed. A p-value cut-off of 0.05 depicted statistical significance. RESULTS: Males had lower relative fluid intake (6 ± 6 vs. 8 ± 7 mL·kg-1·h-1, p < 0.05) and greater relative fluid balance deficit (-13 ± 8 mL·kg-1·h-1 vs. -8 ± 7 mL·kg-1·h-1, p < 0.05) than females. Males had higher whole-body sweat rates (1.3 ± 0.5 L·h-1 vs. 0.9 ± 0.3 L·h-1, p < 0.05) than females. Mean rates of sweat sodium loss (54 ± 27 vs. 39 ± 22 mmol·h-1) were higher in males than females (p < 0.05). CONCLUSIONS: The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners.

Physiological Characteristics of Female Soccer Players and Health and Performance Considerations: A Narrative Review.

Female soccer has seen a substantial rise in participation, as well as increased financial support from governing bodies over the last decade. Thus, there is an onus on researchers and medical departments to develop a better understanding of the physical characteristics and demands, and the health and performance needs of female soccer players. In this review, we discuss the current research, as well as the knowledge gaps, of six major topics: physical demands, talent identification, body composition, injury risk and prevention, health and nutrition. Data on female talent identification are scarce, and future studies need to elucidate the influence of relative age and maturation selection across age groups. Regarding the physical demands, more research is needed on the pattern of high-intensity sprinting during matches and the contribution of soccer-specific movements. Injuries are not uncommon in female soccer players, but targeting intrinsically modifiable factors with injury prevention programmes can reduce injury rates. The anthropometric and physical characteristics of female players are heterogeneous and setting specific targets should be discouraged in youth and sub-elite players. Menstrual cycle phase may influence performance and injury risk; however, there are few studies in soccer players. Nutrition plays a critical role in health and performance and ensuring adequate energy intake remains a priority. Despite recent progress, there is considerably less research in female than male soccer players. Many gaps in our understanding of how best to develop and manage the health and performance of female soccer players remain.

Fluid Balance, Sweat Na+ Losses, and Carbohydrate Intake of Elite Male Soccer Players in Response to Low and High Training Intensities in Cool and Hot Environments.

Hypohydration increases physiological strain and reduces physical and technical soccer performance, but there are limited data on how fluid balance responses change between different types of sessions in professional players. This study investigated sweat and fluid/carbohydrate intake responses in elite male professional soccer players training at low and high intensities in cool and hot environments. Fluid/sodium (Na+) losses and ad-libitum carbohydrate/fluid intake of fourteen elite male soccer players were measured on four occasions: cool (wet bulb globe temperature (WBGT): 15 ± 7 °C, 66 ± 6% relative humidity (RH)) low intensity (rating of perceived exertion (RPE) 2-4, m·min-1 40-46) (CL); cool high intensity (RPE 6-8, m·min-1 82-86) (CH); hot (29 ± 1 °C, 52 ± 7% RH) low intensity (HL); hot high intensity (HH). Exercise involved 65 ± 5 min of soccer-specific training. Before and after exercise, players were weighed in minimal clothing. During training, players had ad libitum access to carbohydrate beverages and water. Sweat [Na+] (mmol·L-1), which was measured by absorbent patches positioned on the thigh, was no different between conditions, CL: 35 ± 9, CH: 38 ± 8, HL: 34 ± 70.17, HH: 38 ± 8 (p = 0.475). Exercise intensity and environmental condition significantly influenced sweat rates (L·h-1), CL: 0.55 ± 0.20, CH: 0.98 ± 0.21, HL: 0.81 ± 0.17, HH: 1.43 ± 0.23 (p =0.001), and percentage dehydration (p < 0.001). Fluid intake was significantly associated with sweat rate (p = 0.019), with no players experiencing hypohydration > 2% of pre-exercise body mass. Carbohydrate intake varied between players (range 0-38 g·h-1), with no difference between conditions. These descriptive data gathered on elite professional players highlight the variation in the hydration status, sweat rate, sweat Na+ losses, and carbohydrate intake in response to training in cool and hot environments and at low and high exercise intensities.

The prevalence of disordered eating in elite male and female soccer players.

PURPOSE: To examine the prevalence of disordered eating (DE) in elite male and female soccer players and the influence of perfectionism. METHODS: Using a cross-sectional design, elite male (n = 137) and female (n = 70) soccer players and non-athlete controls (n = 179) completed the clinical perfectionism questionnaire (CPQ-12) and the eating attitudes test (EAT-26) to assess perfectionism and DE risk, respectively. RESULTS: Male soccer players had higher EAT-26 scores than controls (10.4 ± 9.9 vs. 6.8 ± 6.7; P = 0.001), but there were no differences in the prevalence of clinical levels of DE (EAT-26 score ≥ 20) (15 vs. 5%, respectively; X2 = 0.079) The proportion of females with DE risk was higher in controls [EAT-26: 13.9 ± 11.6 (25% of population)] than female players [EAT-26: 10.0 ± 9.0% (11% of population)] (X2 = 0.001). With linear regression, perfectionism explained 20% of the variation in DE risk in males (P = 0.001); in females, athletic status (player vs. control) and perfectionism were significant predictors of DE risk, explaining 21% of the variation (P = 0.001). Male reserve team players had higher EAT-26 (+ 3.5) and perfectionism (+ 2.7) scores than first-team players (P < 0.05). There were no differences in the prevalence of DE risk between the male and female soccer players (X2 = 0.595). CONCLUSIONS: The prevalence of DE risk was not different in elite male and female soccer players; in fact, the prevalence was greatest in non-athlete female controls. Perfectionism is a significant predictor of DE risk in males and females. LEVEL OF EVIDENCE: III, case-control study.

Assessment of energy availability and associated risk factors in professional female soccer players.

This study aimed to assess energy availability (EA), alongside possible risk factors of reduced or low EA of professional female soccer players during a competitive season. Thirteen players (age: 23.7 ± 3.4 y, stature: 1.69 ± 0.08 m, body mass: 63.7 ± 7.0 kg) engaged in a 5-day (two rest days, one light training, heavy training and match day) monitoring period. Energy intake (EI) and expenditure during exercise (EEE) were measured. EA was calculated and categorised as optimal, reduced or low (>45, 30-45, <30 kcal·kg FFM-1·day-1, respectively). Relationships between EA and bone mineral density, resting metabolic rate (RMR), plasma micronutrient status, biochemical markers and survey data were assessed. EA was optimal for 15%, reduced for 62% and low for 23% of players. Higher EA was observed on rest days compared to others (P<0.05). EA was higher for the light compared to the heavy training day (P<0.001). EEE differed significantly between days (P<0.05). EI (2124 ± 444 kcal), carbohydrate (3.31 ± 0.64 g·kg·day-1) and protein (1.83 ± 0.41 g·kg·day-1) intake remained similar (P>0.05). Survey data revealed 23% scored ≥8 on the Low Energy Availability in Females Questionnaire and met criteria for low RMR (ratio <0.90). Relationships between EA and risk factors were inconclusive. Most players displayed reduced EA and did not alter EI or carbohydrate intake according to training or match demands. Although cases of low EA were identified, further work is needed to investigate possible long-term effects and risk factors of low and reduced EA separately to inform player recommendations.

Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: An update and analysis by sport.

The purpose of this study was to expand our previously published sweat normative data/analysis (n = 506) to establish sport-specific normative data for whole-body sweating rate (WBSR), sweat [Na+], and rate of sweat Na+ loss (RSSL). Data from 1303 athletes were compiled from observational testing (2000-2017) using a standardized absorbent sweat patch technique to determine local sweat [Na+] and normalized to whole-body sweat [Na+]. WBSR was determined from change in exercise body mass, corrected for food/fluid intake and urine/stool loss. RSSL was the product of sweat [Na+] and WBSR. There were significant differences between sports for WBSR, with highest losses in American football (1.51 ± 0.70 L/h), then endurance (1.28 ± 0.57 L/h), followed by basketball (0.95 ± 0.42 L/h), soccer (0.94 ± 0.38 L/h) and baseball (0.83 ± 0.34 L/h). For RSSL, American football (55.9 ± 36.8 mmol/h) and endurance (51.7 ± 27.8 mmol/h) were greater than soccer (34.6 ± 19.2 mmol/h), basketball (34.5 ± 21.2 mmol/h), and baseball (27.2 ± 14.7 mmol/h). After ANCOVA, significant between-sport differences in adjusted means for WBSR and RSSL remained. In summary, due to the significant sport-specific variation in WBSR and RSSL, American football and endurance have the greatest need for deliberate hydration strategies. Abbreviations: WBSR: whole body sweating rate; SR: sweating rate; Na+: sodium; RSSL: rate of sweat sodium loss.

Fat Oxidation Rates in Professional Soccer Players.

PURPOSE: Large interindividual variation exists in maximal fat oxidation (MFO) rates and the exercise intensity at which it occurs (FATMAX). However, there are no data describing the shape of the fat oxidation curve or if individual differences exist when tested on separate occasions. Furthermore, there are limited data on fat metabolism in professional team sport athletes. Therefore, the aim of this study was to test-retest the concavity (shape) and intercept (height) of fat oxidation curves within a group of professional soccer players. METHOD: On two occasions, 16 professional male soccer players completed a graded exercise test in a fasted state (≥5 h). Rates of fat oxidation were determined using indirect calorimetry. Maximal oxygen uptake (V˙O2max) was measured to calculate FATMAX (%V˙O2max). The shape of the fat oxidation curves were modeled on an individual basis using third-degree polynomial. Test-by-test differences, in the shape and vertical shift of the fat oxidation curves, were established to assess within-individual variability. RESULTS: Average absolute MFO was 0.69 ± 0.15 g·min (range, 0.45-0.99 g·min). On a group level, no significant differences were found in MFO between the two tests. No differences were found (P > 0.05) in the shape of the fat oxidation curves in 13 of 16 players (test 1 vs test 2). There were also no differences (P > 0.05) in the vertical shift of the fat oxidation curves in 10 players. CONCLUSIONS: In general, the shape of the fat oxidation curve does not change within an individual; however, the vertical shift is more susceptible to change, which may be due to training status and body composition. Understanding a player's metabolism may be of value to practitioners working within sport, with regard to personalizing nutrition strategies.

Maximal Fat Oxidation Rates in an Athletic Population.

INTRODUCTION: The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population. METHOD: In total, 1121 athletes (933 males and 188 females), from a variety of sports and competitive level, undertook a graded exercise test on a treadmill in a fasted state (≥5 h fasted). Rates of fat oxidation were determined using indirect calorimetry. RESULTS: The average MFO was 0.59 ± 0.18 g·min, ranging from 0.17 to 1.27 g·min. Maximal rates occurred at an average exercise intensity of 49.3% ± 14.8% V˙O2max, ranging from 22.6% to 88.8% V˙O2max. In absolute terms, male athletes had significantly higher MFO compared with females (0.61 and 0.50 g·min, respectively, P < 0.001). Expressed relative to fat-free mass (FFM), MFO were higher in the females compared with males (MFO/FFM: 11.0 and 10.0 mg·kg·FFM·min, respectively, P < 0.001). Soccer players had the highest MFO/FFM (10.8 mg·kg·FFM·min), ranging from 4.1 to 20.5 mg·kg·FFM·min, whereas American Football players displayed the lowest rates of MFO/FFM (9.2 mg·kg·FFM·min). In all athletes, and when separated by sport, large individual variations in MFO rates were observed. Significant positive correlations were found between MFO (g·min) and the following variables: FFM, V˙O2max, FATMAX (the exercise intensity at which the MFO was observed), percent body fat, and duration of fasting. When taken together these variables account for 47% of the variation in MFO. CONCLUSION: MFO and FATMAX vary significantly between athletes participating in different sports but also in the same sport. Although variance in MFO can be explained to some extent by body composition and fitness status, more than 50% of the variance is not explained by these variables and remains unaccounted for.

Impact of intensified training and carbohydrate supplementation on immunity and markers of overreaching in highly trained cyclists.

PURPOSE: To determine effects of intensified training (IT) and carbohydrate supplementation on overreaching and immunity. METHODS: In a randomized, double-blind, crossover design, 13 male cyclists (age 25 ± 6 years, VO2max 72 ± 5 ml/kg/min) completed two 8-day periods of IT. On one occasion, participants ingested 2 % carbohydrate (L-CHO) beverages before, during and after training sessions. On the second occasion, 6 % carbohydrate (H-CHO) solutions were ingested before, during and after training, with the addition of 20 g of protein in the post-exercise beverage. Blood samples were collected before and immediately after incremental exercise to fatigue on days 1 and 9. RESULTS: In both trials, IT resulted in decreased peak power (375 ± 37 vs. 391 ± 37 W, P < 0.001), maximal heart rate (179 ± 8 vs. 190 ± 10 bpm, P < 0.001) and haematocrit (39 ± 2 vs. 42 ± 2 %, P < 0.001), and increased plasma volume (P < 0.001). Resting plasma cortisol increased while plasma ACTH decreased following IT (P < 0.05), with no between-trial differences. Following IT, antigen-stimulated whole blood culture production of IL-1α was higher in L-CHO than H-CHO (0.70 (95 % CI 0.52-0.95) pg/ml versus 0.33 (0.24-0.45) pg/ml, P < 0.01), as was production of IL-1ß (9.3 (95 % CI 7-10.4) pg/ml versus 6.0 (5.0-7.8) pg/ml, P < 0.05). Circulating total leukocytes (P < 0.05) and neutrophils (P < 0.01) at rest increased following IT, as did neutrophil:lymphocyte ratio and percentage CD4+ lymphocytes (P < 0.05), with no between-trial differences. CONCLUSION: IT resulted in symptoms consistent with overreaching, although immunological changes were modest. Higher carbohydrate intake was not able to alleviate physiological/immunological disturbances.

Metabolic response to decaffeinated green tea extract during rest and moderate-intensity exercise.

We previously reported that a 7 day ingestion of caffeinated green tea extract (cGTE) induced marked metabolic differences during rest and exercise. Here, we report the metabolic effects of 1, 7, and 28 day ingestions of decaffeinated GTE (dGTE). In this crossover placebo-controlled study, 19 healthy males ingested dGTE or placebo (PLA) for 28 days, separated by a 28 day wash-out period. On days 1, 7, and 28, participants completed a 30 min cycling exercise 2 h after the ingestion of dGTE or PLA. Blood samples were collected at rest (t = 0 and 120 min) and during exercise (t = 150 min). Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines and catechins. dGTE abolished several metabolic effects when compared to our previous study with cGTE. However, following 7 and 28 day dGTE ingestions, increases in 3-hydroxybutyrate, a metabolic marker of fat oxidation, were observed at t = 0 min. dGTE ingestion did not induce significant acute or acute-on-chronic effects on endogenous metabolites just prior to and during exercise.

Acute effects of green tea extract intake on exogenous and endogenous metabolites in human plasma.

The acute effects of green tea extract (GTE) on plasma metabolites in vivo are largely unknown. In this parallel, double-blind study, the transient changes in total and free concentrations of catechins were measured in plasma from healthy males following the consumption of a single GTE dose (559.2 mg total catechins, 120.4 mg caffeine). Furthermore, the acute effects on endogenous metabolites were assessed 2 h after GTE intake using four-phase metabolite profiling. The ratios of the catechin concentrations in plasma to those in the GTE followed the order ECG/CG > EC > GCG > EGCG > EGC > C > GC. The gallated catechins EGCG, CG/ECG, GC, and GCG were also present in their free form. Sixteen out of 163 mostly endogenous metabolites were affected by acute GTE ingestion, when compared to placebo. These included caffeine, salicylate, hippurate, taurine, 3,4-dihydroxyphenylethylene-glycol, serotonin, some cholesterylesters, fatty acids, triglycerides, and sphingosines. Our results on the exogenous metabolites largely confirm previous studies, while our findings on the endogenous metabolites are novel and may suggest specific biological targets.

Variable duration of decaffeinated green tea extract ingestion on exercise metabolism.

PURPOSE: The aim of this study was to investigate if the duration of decaffeinated green tea extract (dGTE) ingestion plays a role in augmenting fat oxidation rates during moderate-intensity exercise. METHODS: In a crossover, placebo-controlled design, 19 healthy males (mean ± SD; age = 21 ± 2 yr, weight = 75.0 ± 7.0 kg, body mass index = 23.2 ± 2.2 kg·m, maximal oxygen consumption [V˙O2max] = 55.4 ± 4.6 mL·kg·min) ingested dGTE and placebo (PLA) for 28 d, separated by a 28-d washout period. On the first day (dGTE 1 or PLA 1) and after 7 d (dGTE 7 or PLA 7) and 28 d (dGTE 28 or PLA 28), participants completed a 30-min cycle exercise bout (50% Wmax), 2 h after ingestion. Indirect calorimetry was used to calculate rates of whole-body fat and carbohydrate oxidation during exercise. Blood samples were collected at rest and during exercise for analysis of plasma fatty acids, glycerol, and epigallocatechin gallate. RESULTS: The ingestion of dGTE did not significantly change whole-body fat oxidation rates during exercise on day 1, 7, or 28 compared with PLA. There were also no changes in plasma concentrations of fatty acids and glycerol at rest and during exercise as a result of dGTE ingestion at any time point compared with PLA. Plasma epigallocatechin gallate concentrations, immediately before the exercise bout, in the three dGTE trials were elevated compared with PLA but not different between 1, 7, and 28 d. CONCLUSION: In contrast to previous reports, we found that the duration of dGTE ingestion had no effect on whole-body fat oxidation rates or fat metabolism-related blood metabolites during exercise in physically active healthy males.

The metabolic and performance effects of caffeine compared to coffee during endurance exercise.

There is consistent evidence supporting the ergogenic effects of caffeine for endurance based exercise. However, whether caffeine ingested through coffee has the same effects is still subject to debate. The primary aim of the study was to investigate the performance enhancing effects of caffeine and coffee using a time trial performance test, while also investigating the metabolic effects of caffeine and coffee. In a single-blind, crossover, randomised counter-balanced study design, eight trained male cyclists/triathletes (Mean ± SD: Age 41 ± 7 y, Height 1.80 ± 0.04 m, Weight 78.9 ± 4.1 kg, VO2 max 58 ± 3 ml • kg(-1) • min(-1)) completed 30 min of steady-state (SS) cycling at approximately 55% VO2max followed by a 45 min energy based target time trial (TT). One hour prior to exercise each athlete consumed drinks consisting of caffeine (5 mg CAF/kg BW), instant coffee (5 mg CAF/kg BW), instant decaffeinated coffee or placebo. The set workloads produced similar relative exercise intensities during the SS for all drinks, with no observed difference in carbohydrate or fat oxidation. Performance times during the TT were significantly faster (~5.0%) for both caffeine and coffee when compared to placebo and decaf (38.35 ± 1.53, 38.27 ± 1.80, 40.23 ± 1.98, 40.31 ± 1.22 min respectively, p<0.05). The significantly faster performance times were similar for both caffeine and coffee. Average power for caffeine and coffee during the TT was significantly greater when compared to placebo and decaf (294 ± 21 W, 291 ± 22 W, 277 ± 14 W, 276 ± 23 W respectively, p<0.05). No significant differences were observed between placebo and decaf during the TT. The present study illustrates that both caffeine (5 mg/kg/BW) and coffee (5 mg/kg/BW) consumed 1 h prior to exercise can improve endurance exercise performance.

The effect of green tea extract on fat oxidation at rest and during exercise: evidence of efficacy and proposed mechanisms.

Green tea is made from the leaves of the Camellia sinensis L plant, which is rich in polyphenol catechins and caffeine. There is increasing interest in the potential role of green tea extract (GTE) in fat metabolism and its influence on health and exercise performance. A number of studies have observed positive effects of GTE on fat metabolism at rest and during exercise, following both shorter and longer term intake. However, overall, the literature is inconclusive. The fact that not all studies observed effects may be related to differences in study designs, GTE bioavailability, and variation of the measurement (fat oxidation). In addition, the precise mechanisms of GTE in the human body that increase fat oxidation are unclear. The often-cited in vitro catechol-O-methyltransferase mechanism is used to explain the changes in substrate metabolism with little in vivo evidence to support it. Also, changes in expression of fat metabolism genes with longer term GTE intake have been implicated at rest and with exercise training, including the upregulation of fat metabolism enzyme gene expression in the skeletal muscle and downregulation of adipogenic genes in the liver. The exact molecular signaling that activates changes to fat metabolism gene expression is unclear but may be driven by PPAR-γ coactivator 1-α and PPARs. However, to date, evidence from human studies to support these adaptations is lacking. Clearly, more studies have to be performed to elucidate the effects of GTE on fat metabolism as well as improve our understanding of the underlying mechanisms.

Metabolic response to green tea extract during rest and moderate-intensity exercise.

BACKGROUND: Green tea catechins have been hypothesized to increase energy expenditure and fat oxidation by inhibiting catechol-O-methyltransferase (COMT) and thus promoting more sustained adrenergic stimulation. Metabolomics may help to clarify the mechanisms underlying their putative physiological effects. OBJECTIVE: The study investigated the effects of 7-day ingestion of green tea extract (GTE) on the plasma metabolite profile at rest and during exercise. METHODS: In a placebo-controlled, double-blind, randomized, parallel study, 27 healthy physically active males consumed either GTE (n=13, 1200 mg catechins, 240 mg caffeine/day) or placebo (n=14, PLA) drinks for 7 days. After consuming a final drink (day 8), they rested for 2 h and then completed 60 min of moderate-intensity cycling exercise (56% ± 4% VO(2)max). Blood samples were collected before and during exercise. Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines. RESULTS: Using the metabolomic approach, we observed that GTE did not enhance adrenergic stimulation (adrenaline and noradrenaline) during rest or exercise. At rest, GTE led to changes in metabolite concentrations related to fat metabolism (3-ß-hydroxybutyrate), lipolysis (glycerol) and tricarboxylic acid cycle (TCA) cycle intermediates (citrate) when compared to PLA. GTE during exercise caused reductions in 3-ß-hydroxybutyrate concentrations as well as increases in pyruvate, lactate and alanine concentrations when compared to PLA. CONCLUSIONS: GTE supplementation resulted in marked metabolic differences during rest and exercise. Yet these metabolic differences were not related to the adrenergic system, which questions the in vivo relevance of the COMT inhibition mechanism of action for GTE.

No effect of 1 or 7 d of green tea extract ingestion on fat oxidation during exercise.

PURPOSE: The aim of this study was to investigate the effects of 1 and 7 d of green tea extract (GTE) ingestion on whole body fat oxidation during moderate-intensity exercise. METHODS: Thirty-one men completed two exercise trials (60-min cycle, 50% Wmax). After the baseline trial (day 0), subjects were randomly assigned to one of three conditions involving a week supplementation of the following: 1) 7 d of placebo, 2) 6 d of placebo followed by 1 d of GTE (GTE1), and 3) 7 d of GTE ingestion (GTE7). The morning after the supplementation week, subjects consumed an additional supplement and completed a second exercise trial (day 8). V˙O2 and V˙CO2 measurements were taken during exercise to calculate whole body fat oxidation rates. Blood samples, for analysis of plasma fatty acids (FA), glycerol, and epigallocatechin gallate, were collected at rest and during exercise. RESULTS: On day 8, the plasma kinetics and maximal plasma concentrations of epigallocatechin gallate were similar in the GTE1 and GTE7 group (206 ± 28 and 216 ± 25 ng·mL, respectively). One day of GTE ingestion did not affect markers of lipolysis during the exercise bout. Seven days of GTE ingestion significantly increased plasma glycerol during exercise (P = 0.045) and plasma FA during exercise (P = 0.020) as well as at rest (P = 0.046). However, fat oxidation did not change in any of the groups. CONCLUSIONS: There was no effect of 1 d of GTE ingestion on markers of lipolysis or fat oxidation during exercise. Seven days of GTE ingestion increased lipolysis, indicated by increased plasma FA and glycerol concentrations, but did not result in significant changes in fat oxidation.