Glycogen

Glycogen synthase (GS), a key enzyme in glycogen synthesis, is activated by the allosteric stimulator glucose-6-phosphate (G6P) and by dephosphorylation through inactivation of GS kinase-3 with insulin. The relative importance of these two regulatory mechanisms in controlling GS is not established, mainly due to the complex interplay between multiple phosphorylation sites and allosteric effectors. Here we identify a residue that plays an important role in the allosteric activation of GS by G6P. We generated knockin mice in which wild-type muscle GS was replaced by a mutant that could not be activated by G6P but could still be activated normally by dephosphorylation. We demonstrate that knockin mice expressing the G6P-insensitive mutant display an ∼80% reduced muscle glycogen synthesis by insulin and markedly reduced glycogen levels. Our study provides genetic evidence that allosteric activation of GS is the primary mechanism by which insulin promotes muscle glycogen accumulation in vivo.► A critical glucose-6-phosphate (G6P) action site on glycogen synthase (GS) identified ► A knockin mouse expressing G6P-insensitive mutant GS generated ► GS knockin mice display dramatically reduced ability to accumulate muscle glycogen ► Insulin promotes glycogen synthesis mainly via allosteric activation of GS by G6P

The top players in an elite soccer team volunteered as subjects in a study to determine intramuscular glycogen concentrations after a regular season match, and whether optimal glycogen levels could be re-attained prior to the team's next match. Fifteen players were biopsied in the M. vastus lateralis following a regular season game (Day I). Of these, eight were biopsied 24 h later in the evening of a free day during which no training session was held (Day II), and again 24 h later after a very light training session (Day III). Muscle glycogen concentrations for the eight players averaged (+ SD) 45.9 + 7.9, 68.9 + 2.7, and 72.8 + 8.3 mmol glucose units x kg -1 wet muscle weight on Day I, Day II, and Day III respectively. Dietary records were analysed during a week of peak season competition and training. The average daily total energy consumption and total quantity of carbohydrates consumed were less than what is normally consumed by athletes in similar sports. The inability of the players to maintain even normal, resting levels of muscle glycogen is probably related to their dietary practices.

Purpose: Commencing selected workouts with low muscle glycogen availability augments several markers of training adaptation compared with undertaking the same sessions with normal glycogen content. However, low glycogen availability reduces the capacity to perform high-intensity (985% of peak aerobic power (V O 2peak )) endurance exercise. We determined whether a low dose of caffeine could partially rescue the reduction in maximal self-selected power output observed when individuals commenced high-intensity interval training with low (LOW) compared with normal (NORM) glycogen availability. Methods: Twelve endurancetrained cyclists/triathletes performed four experimental trials using a double-blind Latin square design. Muscle glycogen content was manipulated via exercise-diet interventions so that two experimental trials were commenced with LOW and two with NORM muscle glycogen availability. Sixty minutes before an experimental trial, subjects ingested a capsule containing anhydrous caffeine (CAFF, 3 mg j1 Ikg j1 body mass) or placebo (PLBO). Instantaneous power output was measured throughout high-intensity interval training (8 Â 5-min bouts at maximum self-selected intensity with 1-min recovery). Results: There were significant main effects for both preexercise glycogen content and caffeine ingestion on power output. LOW reduced power output by approximately 8% compared with NORM (P G 0.01), whereas caffeine increased power output by 2.8% and 3.5% for NORM and LOW, respectively, (P G 0.01). Conclusion: We conclude that caffeine enhanced power output independently of muscle glycogen concentration but could not fully restore power output to levels commensurate with that when subjects commenced exercise with normal glycogen availability. However, the reported increase in power output does provide a likely performance benefit and may provide a means to further enhance the already augmented training response observed when selected sessions are commenced with reduced muscle glycogen availability.

The present study investigated the role of swimming training on cerebral metabolism and hippocampus concentrations of insulin and IGF-1 in diabetic rats. Wistar rats were divided in sedentary control (SC), trained control (TC), sedentary diabetic (SD), and trained diabetic (TD). Diabetes was induced by Alloxan (35 mg kg 21 b.w.). Training program consisted in swimming 5 days/week, 1 h/day, 8 weeks, supporting a load corresponding to 90% of maximal lactate steady state (MLSS). For MLSS determination, rats were submitted to three sessions of 25-min supporting loads of 4, 5, or 6% of body wt, with intervals of 1 week. Blood samples were collected every 5 min for lactate determination. An acute exercise test (25 min to 90% of MLSS) was done in 7th week to confirm the efficacy of training. All dependent variables were analyzed by one-way analysis of variance (ANOVA) and a significance level of P < 0.05 was used for all comparisons. The Bonferroni test was used for post hoc comparisons. At the end of the training period, rats were sacrificed and sample blood was collected for determinations of serum glucose, insulin, GH, and IGF-1. Samples of gastrocnemius muscle and liver were removed to evaluate glycogen content. Hippocampus was extracted to determinate glycogen, insulin, and IGF-1 contents. Diabetes decreased serum GH, IGF-1, and liver glycogen stores in SD. Diabetes also increased hippocampus glycogen and reduced hippocampus IGF-1 content. Physical training recovered liver and hippocampus glycogen stores and promoted increases in serum IGF-1 in TD group. Physical training restored hippocampus IGF-1 content in diabetic group. It was concluded that in diabetic rats, physical training induces important metabolic and hormonal alterations that are associated with an improvement in glucose homeostasis and with an increased activity in the systemic and hippocampus IGF-1 peptide.

Griffonia simplicifolia, which reportedly binds to terminal N-acetylglucosamine residues in glycoconjugate oligosaccharides also shows affinity for glycogen. In the present study, the lectin was conjugated to horseradish peroxidase and applied to paraffin sections of kidney from streptozotocin-diabetic rats, insulintreated and untreated, and age-matched control rats. Griffonia simplicifolia agglutinin II detected glycogen in cortical ascending thick limbs of untreated diabetic rat kidneys as early as 24 h following injection of streptozotocin. The number of stained cells increased steadily so that by day 14 of diabetes the lectin reacted with nearly all of the cells lining ascending thick limbs in the cortex and adjacent outer stripe of the outer medulla. Glycogen was never identified in the inner medullary stripe. Comparison of Griffonia simplicifolia agglutinin II and periodic acid-Schiff staining revealed that periodic acid-Schiff could not clearly detect glycogen until 14 days following injection of streptozotocin, which substantiated earlier claims that Griffonia simplicifolia agglutinin II might be a more sensitive indicator of glycogen than periodic acid-Schiff. The distribution of glycoconjugate containing terminal N-acetylglucosamine stainable with the lectin was unchanged in diabetic kidneys. Griffonia simplicifolia agglutinin II served in the present study to further characterise the sequence of abnormal glycogen accumulation in streptozotocin-diabetic rat kidneys. In addition, it was shown that the lectin's ability to antedate periodic acid-Schiff detection of glycogen has utility in histochemical investigations in diabetes.

The yeast Saccharomyces cerevisiae has been used as a model organism to investigate responses to different environmental stressors. The importance of their conclusions has been expanded to human cells. The experiments were done with exponentially growing cells, which do not resemble human cells. Human and other eukaryotic cells spend the greater part of their lives in a quiescent state, known as G 0 corresponding to the yeast stationary phase. Providing energy, which comes from mitochondrial respiration, is also common. Thus, in the present study S. cerevisiae was used in the stationary phase for characterization at the cellular and proteome levels. At the cellular level, optical density, cell viability, glycogen content, intracellular oxidation and cell energy metabolic activity were measured, while at the proteome level, protein profiles were analyzed using twodimensional electrophoresis. The data obtained at both levels provide better insight into quiescence program state, which still remains poorly understood. At their base, optimal time period reflecting a stable metabolic and oxidative state of the yeast was determined. Consequently, this period is the appropriate to study changes in cell oxidant status and energy metabolic activity in response to different environmental stressors.

This work investigated the effects of copper as preventive treatment against mercury-induced alterations in young rats. Wistar rats were treated (subcutaneous) with saline or CuCl 2 ·2H 2 O (6.9 mg/kg/day) from 3 to 7 days old and with saline or HgCl 2 (5.0 mg/kg/day) from 8 to 12 days old. Rats were sacrificed 24 h after the last dose. Mercury-exposed rats presented inhibition of liver (43%) and kidney (52%) porphobilinogen (PBG)-synthase activity and serum lactic dehydrogenase activity (50%). Also, an increase of the serum creatinine and urea levels around threefold and fivefold was observed, respectively. Pre-exposure to copper partially prevented the mercury effect on liver but not on kidney PBG synthase, and prevented the increase of the creatinine levels. Blood and brain PBG synthase and serum alanineaminotransferase activities, as well as glycemia, and liver glycogen content were not altered by treatments. These results show that copper, although being an essential metal, is inefficient as a preventive agent against mercury poisoning in parameters investigated after the end of mercury exposure. C 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 00:1-6, 2012; View this article online at wileyonlinelibrary.com.

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&#39; 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...

Breast cancer is a major health problem in underdeveloped countries including Sudan. Immunohistochemical typing is important for diagnosing and understanding the biology of such heterogeneous disease. To the best of our knowledge, no study has investigated the association between estrogen receptors (ER) expression and carbohydrates in breast tissue. Mammographic high density, a major risk factor, is partially attributed to carbohydrates. This study aimed to determine the type of carbohydrates in malignant and benign breast lesions and detect if there is any association between ER expression and carbohydrates using histochemical and immunohistochemical methods. A total of 60 diagnosed samples of different breast lesions were reexamined for ER status by immunohistochemistry (IHC) and for carbohydrates by histochemical staining methods i.e. periodic acid Schiff (PAS) and alcian blue. Strong relationship was discovered between ER positivity and presence of acid mucin, but not with sulfated mucin. Furthermore, strong relationship was found between ER positivity and PAS positive materials, but not with glycogen. Since there was a significant correlation between ER and carbohydrates, these positive PAS materials might be PAS positive acid mucin. These findings are useful in understanding the behavior of breast lesions. Also, these findings suggested an underlying molecular relationships and that ER expression might be predicted using histochemical demonstration of carbohydrates in female breast tissue particularly when immunohistochemistry is out of reach.

The effect of the distribution of rest periods on the efficacy of interval sprint training is analysed. Ten male subjects, divided at random into two groups, performed distinct incremental sprint training protocols, in which the muscle load was the same (14 sessions), but the distribution of rest periods was varied. The`short programme' group (SP) trained every day for 2 weeks, while the`long programme' group (LP) trained over a 6-week period with a 2-day rest period following each training session. The volunteers performed a 30-s supramaximal cycling test on a cycle ergometer before and after training. Muscle biopsies were obtained from the vastus lateralis before and after each test to examine metabolites and enzyme activities. Both training programmes led to a marked increase (all signi®cant, P < 0.05) in enzymatic activities related to glycolysis (phosphofructokinase ± SP 107%, LP 68% and aldolase ± SP 46%, LP 28%) and aerobic metabolism (citrate synthase ± SP 38%, LP 28.4% and 3-hydroxyacyl-CoA dehydrogenase ± SP 60%, LP 38.7%). However, the activity of creatine kinase (44%), pyruvate kinase (35%) and lactate dehydrogenase (45%) rose signi®cantly (P < 0.05) only in SP. At the end of the training programme, SP had suffered a signi®cant decrease in anaerobic ATP consumption per gram muscle (P < 0.05) and glycogen degradation (P < 0.05) during the post-training test, and failed to improve performance. In contrast, LP showed a marked improvement in performance (P < 0.05) although without a signi®cant increase in anaerobic ATP consumption, glycolysis or glycogenolysis rate. These results indicate that high-intensity cycling training in 14 sessions improves enzyme activities of anaerobic and aerobic metabolism. These changes are affected by the distribution of rest periods, hence shorter rest periods produce larger increase in pyruvate kinase, creatine kinase and lactate dehydrogenase. However, performance did not improve in a short training programme that did not include days for recovery, which suggests that muscle ®bres suffer fatigue or injury.

Two patients with phosphofructokinase (PFK) deficiency had exercise intolerance and increased serum activity of creatine kinase; one presented with hemolytic anemia, hyperuricemia, and gouty arthritis. The glycogen concentration in the muscle of these patients was about twice normal. PFK activity was virtually absent in muscle, but antibodies against the M subunits of the normal human PFK showed cross-reacting material in muscle from both patients. The PFK level in red blood cells, studied in one case, was lower than normal in the patient and both parents. Morphologically, there was extensive deposition of normal glycogen underneath the sarcolemma and in the intermyofibrillar space. In addition, 2% to 3% of the myofibers contained hyaline, PAS-positive, diastase-resistant inclusions that had a filamentous fine structure: histochemical reactions suggested an insoluble form of glycogen. Similar inclusions have not been described previously in PFK deficiency. Accumulation of an abnormal polysaccharide in muscle may be due to a second undiscovered enzymatic defect or may be a metabolic consequence of PFK deficiency.

Fat adaptation followed by carbohydrate restoration increases AMPK activity in skeletal muscle from trained humans. We have previously reported that 5 days of a high-fat diet followed by 1 day of high-carbohydrate intake (Fat-adapt) increased rates of fat oxidation and decreased rates of muscle glycogenolysis during submaximal cycling compared with consumption of an isoenergetic high-carbohydrate diet (HCHO) for 6 days (Burke et al. J Appl Physiol 89: 2413-2421 Stellingwerff et al. Am J Physiol Endocrinol Metab 290: E380 -E388, 2006). To determine potential mechanisms underlying shifts in substrate selection, eight trained subjects performed Fat-adapt and HCHO. On day 7, subjects performed 1-h cycling at 70% peak O2 uptake. Muscle biopsies were taken immediately before and after exercise. Resting muscle glycogen content was similar between treatments, but muscle triglyceride levels were higher after Fat-adapt (P Ͻ 0.05). Resting AMPK-␣1 and -␣2 activity was higher after Fat-adapt (P ϭ 0.02 and P ϭ 0.05, respectively), while the phosphorylation of AMPK's downstream target, acetyl-CoA carboxylase (pACC at Ser 221 ), tended to be elevated after Fat-adapt (P ϭ 0.09). Both the respiratory exchange ratio (P Ͻ 0.01) and muscle glycogen utilization (P Ͻ 0.05) were lower during exercise after Fat-adapt. Exercise increased AMPK-␣1 activity after HCHO (P ϭ 0.03) but not Fat-adapt. Exercise was associated with an increase in pACC at Ser 221 for both dietary treatments (P Ͻ 0.05), with postexercise pACC Ser 221 higher after Fat-adapt (P ϭ 0.02). In conclusion, compared with HCHO, Fat-adapt increased resting muscle triglyceride stores and resting AMPK-␣1 and -␣2 activity. Fat-adapt also resulted in higher rates of whole body fat oxidation, reduced muscle glycogenolysis, and attenuated the exercise-induced rise in AMPK-␣1 and AMPK-␣2 activity compared with HCHO. Our results demonstrate that AMPK-␣1 and AMPK-␣2 activity and fuel selection in skeletal muscle in response to exercise can be manipulated by diet and/or the interactive effects of diet and exercise training.

showed that 2 wk of daily sprint interval training (SIT) increased citrate synthase (CS) maximal activity but did not change "anaerobic" work capacity, possibly because of chronic fatigue induced by daily training. The effect of fewer SIT sessions on muscle oxidative potential is unknown, and aside from changes in peak oxygen uptake (V O2 peak), no study has examined the effect of SIT on "aerobic" exercise capacity. We tested the hypothesis that six sessions of SIT, performed over 2 wk with 1-2 days rest between sessions to promote recovery, would increase CS maximal activity and endurance capacity during cycling at ϳ80% V O2 peak. Eight recreationally active subjects [age ϭ 22 Ϯ 1 yr; V O2 peak ϭ 45 Ϯ 3 ml ⅐ kg Ϫ1 ⅐ min Ϫ1 (mean Ϯ SE)] were studied before and 3 days after SIT. Each training session consisted of four to seven "all-out" 30-s Wingate tests with 4 min of recovery. After SIT, CS maximal activity increased by 38% (5.5 Ϯ 1.0 vs. 4.0 Ϯ 0.7 mmol ⅐ kg protein Ϫ1 ⅐ h Ϫ1 ) and resting muscle glycogen content increased by 26% (614 Ϯ 39 vs. 489 Ϯ 57 mmol/kg dry wt) (both P Ͻ 0.05). Most strikingly, cycle endurance capacity increased by 100% after SIT (51 Ϯ 11 vs. 26 Ϯ 5 min; P Ͻ 0.05), despite no change in V O2 peak. The coefficient of variation for the cycle test was 12.0%, and a control group (n ϭ 8) showed no change in performance when tested ϳ2 wk apart without SIT. We conclude that short sprint interval training (ϳ15 min of intense exercise over 2 wk) increased muscle oxidative potential and doubled endurance capacity during intense aerobic cycling in recreationally active individuals. Wingate test; citrate synthase; muscle glycogen

Ingestion of a protein-amino acid mixture (Pro; wheat protein hydrolysate, leucine, and phenylalanine) in combination with carbohydrate (CHO; 0.8 g x kg(-1) x h(-1)) has been shown to increase muscle glycogen synthesis after exercise compared with the same amount of CHO without Pro. The aim of this study was to investigate whether coingestion of Pro also increases muscle glycogen synthesis when 1.2 g CHO. kg(-1). h(-1) is ingested. Eight male cyclists performed two experimental trials separated by 1 wk. After glycogen-depleting exercise, subjects received either CHO (1.2 g x kg(-1) x h(-1)) or CHO+Pro (1.2 g CHO x kg(-1) x h(-1) + 0.4 g Pro x kg(-1) x h(-1)) during a 3-h recovery period. Muscle biopsies were obtained immediately, 1 h, and 3 h after exercise. Blood samples were collected immediately after the exercise bout and every 30 min thereafter. Plasma insulin was significantly higher in the CHO+Pro trial compared with the CHO trial (P &lt; 0.05). No difference was found in pla...

Brief, intense exercise training may induce metabolic and performance adaptations comparable to traditional endurance training. However, no study has directly compared these diverse training strategies in a standardized manner. We therefore examined changes in exercise capacity and molecular and cellular adaptations in skeletal muscle after low volume sprint-interval training (SIT) and high volume endurance training (ET). Sixteen active men (21 ± 1 years,V O 2 peak = 4.0 ± 0.21 min −1 ) were assigned to a SIT or ET group (n = 8 each) and performed six training sessions over 14 days. Each session consisted of either four to six repeats of 30 s 'all out' cycling at ∼250%V O 2 peak with 4 min recovery (SIT) or 90-120 min continuous cycling at ∼65%V O 2 peak (ET). Training time commitment over 2 weeks was ∼2.5 h for SIT and ∼10.5 h for ET, and total training volume was ∼90% lower for SIT versus ET (∼630 versus ∼6500 kJ). Training decreased the time required to complete 50 and 750 kJ cycling time trials, with no difference between groups (main effects, P ≤ 0.05). Biopsy samples obtained before and after training revealed similar increases in muscle oxidative capacity, as reflected by the maximal activity of cytochrome c oxidase (COX) and COX subunits II and IV protein content (main effects, P ≤ 0.05), but COX II and IV mRNAs were unchanged. Training-induced increases in muscle buffering capacity and glycogen content were also similar between groups (main effects, P ≤ 0.05). Given the large difference in training volume, these data demonstrate that SIT is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance that are comparable to ET in young active men.

BURKE, L. M., and J. A. HAWLEY. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. manipulating an individuals habitual diet before an exercise bout in an attempt to modify patterns of fuel substrate utilization and enhance subsequent exercise capacity is not new. Modern studies have focused on nutritional and training strategies aimed to optimize endogenous carbohydrate (CHO) stores while simultaneously maximizing the capacity for fat oxidation during continuous, submaximal (60 -70% of maximal O 2 uptake [V O 2max ]) exercise. Such "nutritional periodization" typically encompasses 5-6 d of a high-fat diet (60 -70% E) followed by 1-2 d of high-CHO intake (70 -80% E; CHO restoration). Despite the brevity of the adaptation period, ingestion of a high-fat diet by endurance-trained athletes results in substantially higher rates of fat oxidation and concomitant muscle glycogen sparing during submaximal exercise compared with an isoenergetic high-CHO diet. Higher rates of fat oxidation during exercise persist even under conditions in which CHO availability is increased, either by having athletes consume a high-CHO meal before exercise and/or ingest glucose solutions during exercise. Yet, despite marked changes in the patterns of fuel utilization that favor fat oxidation, fat-adaptation/CHO restoration strategies do not provide clear benefits to the performance of prolonged endurance exercise. Key Words: DIETARY PERIODIZATION, FAT OXIDATION, FAT-LOADING, GLYCOGEN SPARING E

The aim of this study was to evaluate the effect of different forage-types on lamb carcass, meat quality and sensory attributes. Sixty-two, White Dorper lambs finished on bladder clover, brassica, chicory+arrowleaf clover, lucerne+phalaris or lucerne, were slaughtered at a commercial abattoir. At 24h post-mortem, the m. longissimus thoracis et lumborum (LL) was removed from the left side and sliced into three equal sub-samples, vacuum packaged and randomly assigned to ageing periods (5, 12 or 40days) and the right side was aged for 5days. The m. semimembranosus and m. adductor femoris were removed and, the former was then aged for 40days. Lambs fed chicory+arrowleaf clover or lucerne had a higher dressing percentage and fat depth. Bladder clover gave the highest level of glycogen in the LL. No sensory or other meat quality trait differences were found between the treatments. In general, no treatments showed any unfavourable effect on the traits examined.

Insulin resistance is a feature of a number of clinical disorders, including type 2 diabetes/glucose intolerance, obesity, dyslipidaemia and hypertension clustering in the so-called metabolic syndrome. Insulin resistance in skeletal muscle manifests itself primarily as a reduction in insulinstimulated glycogen synthesis due to reduced glucose transport. Ectopic lipid accumulation plays an important role in inducing insulin resistance. Multiple defects in insulin signalling are responsible for impaired glucose metabolism in target tissues of subjects with features of insulin resistance. Inflammatory molecules and lipid metabolites inhibit insulin signalling by stimulating a number of different serine kinases which are responsible for serine phosphorylation of Insulin Receptor Substrate-1 (IRS-1).

Diabetes mellitus is the most common and serious metabolic disorder among people all over the world. Many plants have successfully been used to overcome this problem. Costus speciosus is widely used in Indian medicine to treat various diseases including diabetes. Bioassay guided fractionation was followed to isolate costunolide from the hexane extract of C. speciosus root. The structure was elucidated using X-ray crystallography. Costunolide was administered to streptozotocin (STZ) (50 mg/kg bw)-induced diabetic male wistar rats at different doses (5, 10, 20 mg/kg bw) for 30 days to assess its effect on fasting plasma glucose and cholesterol levels. It was found that plasma glucose was significantly (p < 0.05) reduced in a dose-dependent manner when compared to the control. In addition, oral administration of costunolide (20 mg/kg bw) significantly decreased glycosylated hemoglobin (HbA 1c ), serum total cholesterol, triglyceride, LDL cholesterol and at the same time markedly increased plasma insulin, tissue glycogen, HDL cholesterol and serum protein. Also costunolide restored the altered plasma enzyme (aspartate aminotransferase, alanine aminotrasferase, lactate dehydrogenase, alkaline phosphatase and acid phosphatase) levels to near normal. Costunolide might have stimulated the beta islets to secrete insulin by inhibiting the expression of nitric oxide synthase. The results of this experimental study indicated that costunolide possessed normo-glycemic and hypolipidemic activity and hence it could be used as a drug for treating diabetes.

This study aimed to compare the recovery kinetics of physical performance and subjective ratings in response to a soccerspecific exercise simulation on natural grass and artificial turf. Physical performance tests and subjective ratings were assessed on 13 professional soccer players before, immediately after, 24 h and 48 h after the test. Physical performance tests included squat jump, countermovement jump, 6-s sprint on a non-motorised treadmill and isokinetic eccentric hamstring assessment (2.09 rad Á s 71 ). Hamstring peak torque decrement was higher (P 5 0.05) on natural grass than on artificial turf immediately (-4.0%, CI 95%: -10.0 to 2.0%, Effect Size [ES] ¼ 0.29), 24 h (-3.1%, CI 95%: -9.3 to 3.1%, ES ¼ 0.29) and 48 h (-3.8%, CI 95%: -8.5 to 0.9%, ES ¼ 0.43) after the test. Squat jump performance decrement was significantly lower (P 5 0.05) on natural grass than artificial turf 48 h after the test (þ3.7%, CI 95%: 1.1 to 6.3%, ES ¼ 0.40). Sprint performance showed no change from baseline performance for both trials throughout the protocol. No significant interaction between surface and time was found for countermovement jump and subjective ratings. These results suggest that a one-off exercise on artificial turf does not induce greater fatigue nor does it delay the recovery process when compared to natural grass among regular artificial turf players.

In soccer, the players perform intermittent work. Despite the players performing low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that the average oxygen uptake for elite soccer players is around 70% of maximum ( _ V O 2max ). This may be partly explained by the 150 -250 brief intense actions a top-class player performs during a game, which also indicates that the rates of creatine phosphate (CP) utilization and glycolysis are frequently high during a game. Muscle glycogen is probably the most important substrate for energy production, and fatigue towards the end of a game may be related to depletion of glycogen in some muscle fibres. Blood free-fatty acids (FFAs) increase progressively during a game, partly compensating for the progressive lowering of muscle glycogen. Fatigue also occurs temporarily during matches, but it is still unclear what causes the reduced ability to perform maximally. There are major individual differences in the physical demands of players during a game related to physical capacity and tactical role in the team. These differences should be taken into account when planning the training and nutritional strategies of top-class players, who require a significant energy intake during a week.

Nine male, endurance-trained cyclists performed an interval workout followed by 4 h of recovery, and a subsequent endurance trial to exhaustion at 70% VO 2max , on three separate days. Immediately following the fi rst exercise bout and 2 h of recovery, subjects drank isovolumic amounts of chocolate milk, fl uid replacement drink (FR), or carbohydrate replacement drink (CR), in a single-blind, randomized design. Carbohydrate content was equivalent for chocolate milk and CR. Time to exhaustion (TTE), average heart rate (HR), rating of perceived exertion (RPE), and total work (W T ) for the endurance exercise were compared between trials. TTE and W T were signifi cantly greater for chocolate milk and FR trials compared to CR trial. The results of this study suggest that chocolate milk is an effective recovery aid between two exhausting exercise bouts.

The rate of carbohydrate utilization during prolonged, strenuous exercise is closely geared to the energy needs of the working muscles. In contrast, fat utilization during exercise is not tightly regulated, as there are no mechanisms for closely matching availability and metabolism of fatty acids to the rate of energy expenditure. As a result, the rate of fat oxidation during exercise is determined by the availability of fatty acids and the rate of carbohydrate utilization. Blood glucose and muscle glycogen are essential for prolonged strenuous exercise, and exhaustion can result either from development of hypoglycemia or depletion of muscle glycogen.

Although hot conditions are not typically conducive to optimal sports performance, nutritional strategies play an important role in assisting an athlete to perform as well as possible in a hot environment. A key issue is the prevention of hypohydration during an exercise session. Fluid intake strategies should be undertaken in a cyclical sequence: hydrate well prior to the workout, drink as much as is comfortable and practical during the session, and rehydrate aggressively afterwards in preparation for future exercise bouts. There is some interest in hyperhydration strategies, such as hyperhydration with glycerol, to prepare the athlete for a situation where there is little opportunity for fluid intake to match large sweat losses. Recovery of significant fluid losses after exercise is assisted by the simultaneous replacement Ž . of electrolyte losses. Carbohydrate CHO requirements for exercise are increased in the heat, due to a shift in substrate utilization towards CHO oxidation. Daily food patterns should focus on replacing glycogen stores after exercise, and competition strategies should include activities to enhance CHO availability, such as CHO loading for endurance events, pre-event CHO intake, and intake of sports drinks in events lasting longer than 60 min. Although CHO ingestion may not enhance the performance of all events undertaken in hot weather, there are no disadvantages to the consumption of beverages containing 4᎐8% CHO and electrolytes. In fact, the palatability of these drinks may enhance the voluntary intake of fluid. Although there is some evidence of increased protein catabolism and cellular damage due to production of oxygen radicals during exercise in the heat, there is insufficient evidence to make specific dietary recommendations to account for these issues. ᮊ L.M. Burke . 1095-6433r01r$ -see front matter ᮊ 2001 Elsevier Science Inc. All rights reserved. Ž . PII: S 1 0 9 5 -6 4 3 3 0 1 0 0 2 7 9 -3 ( ) L.M. Burke r Comparati¨e Biochemistry and Physiology Part A 128 2001 735᎐748 736

Studies on the biological activities of chitosan and its oligomers have been increasing, as no single type of chitosan or its oligomers exerts all of the above bioactivities. Moreover, different chitosan derivatives and enzymatic products have different structures and physicochemical properties, which may result in novel bioactivities or novel findings in known bioactive compounds. Chitosan oligosaccharides also have been shown to induce various plant defense-related cellular responses and possess by themselves antimicrobial properties against a wide spectrum of phytopathogens . The biological activity of COS is known to depend on their structure. Chitosan derivatives have a wide scope of application and regulate the immune system of plants and induce the excretion of resistant enzymes. Moreover, chitosan not only activates the cells, but also improves its disease and insect resistant ability. There is a great concern about the consequences of utilization of chemicals on health and environment, so other means of controlling diseases have become a vehement necessity. There are other well-known problems in agriculture sector, such as: disease resistance to bactericides, fungicides and high costs to develop new products, so the scientists are interested in biological control agents and naturally occurring fungicides. Keeping in view the important role of chitosan and COS in agriculture, this review is aimed at investigating the efficacy of chitosan and its derivative on crop protection.

In soccer, the players perform intermittent work. Despite the players performing low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that the average oxygen uptake for elite soccer players is around 70% of maximum ( _ V O 2max ). This may be partly explained by the 150 -250 brief intense actions a top-class player performs during a game, which also indicates that the rates of creatine phosphate (CP) utilization and glycolysis are frequently high during a game. Muscle glycogen is probably the most important substrate for energy production, and fatigue towards the end of a game may be related to depletion of glycogen in some muscle fibres. Blood free-fatty acids (FFAs) increase progressively during a game, partly compensating for the progressive lowering of muscle glycogen. Fatigue also occurs temporarily during matches, but it is still unclear what causes the reduced ability to perform maximally. There are major individual differences in the physical demands of players during a game related to physical capacity and tactical role in the team. These differences should be taken into account when planning the training and nutritional strategies of top-class players, who require a significant energy intake during a week.