Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise.

We determined the effect of fat adaptation on metabolism and performance during 5 h of cycling in seven competitive athletes who consumed a standard carbohydrate (CHO) diet for 1 day and then either a high-CHO diet (11 g. kg(-1)x day(-1) CHO, 1 g x kg(-1) x day(-1) fat; HCHO) or an isoenergetic high-fat diet (2.6 g x kg(-1) x day(-1) CHO, 4.6 g x kg(-1) x day(-1) fat; fat-adapt) for 6 days. On day 8, subjects consumed a high-CHO diet and rested. On day 9, subjects consumed a preexercise meal and then cycled for 4 h at 65% peak O(2) uptake, followed by a 1-h time trial (TT). Compared with baseline, 6 days of fat-adapt reduced respiratory exchange ratio (RER) with cycling at 65% peak O(2) uptake [0.78 +/- 0.01 (SE) vs. 0.85 +/- 0.02; P < 0.05]. However, RER was restored by 1 day of high-CHO diet, preexercise meal, and CHO ingestion (0.88 +/- 0.01; P < 0.05). RER was higher after HCHO than fat-adapt (0.85 +/- 0.01, 0.89 +/- 0.01, and 0.93 +/- 0.01 for days 2, 8, and 9, respectively; P < 0.05). Fat oxidation during the 4-h ride was greater (171 +/- 32 vs. 119 +/- 38 g; P < 0.05) and CHO oxidation lower (597 +/- 41 vs. 719 +/- 46 g; P < 0.05) after fat-adapt. Power output was 11% higher during the TT after fat-adapt than after HCHO (312 +/- 15 vs. 279 +/- 20 W; P = 0.11). In conclusion, compared with a high-CHO diet, fat oxidation during exercise increased after fat-adapt and remained elevated above baseline even after 1 day of a high-CHO diet and increased CHO availability. However, this study failed to detect a significant benefit of fat adaptation to performance of a 1-h TT undertaken after 4 h of cycling.     

Effects of endurance exercise training on muscle glycogen accumulation in humans.

The purpose of this investigation was to determine whether endurance exercise training increases the ability of human skeletal muscle to accumulate glycogen after exercise. Subjects (4 women and 2 men, 31 +/- 8 yr old) performed high-intensity stationary cycling 3 days/wk and continuous running 3 days/wk for 10 wk. Muscle glycogen concentration was measured after a glycogen-depleting exercise bout before and after endurance training. Muscle glycogen accumulation rate from 15 min to 6 h after exercise was twofold higher (P < 0.05) in the trained than in the untrained state: 10.5 +/- 0.2 and 4.5 +/- 1.3 mmol. kg wet wt(-1). h(-1), respectively. Muscle glycogen concentration was higher (P < 0.05) in the trained than in the untrained state at 15 min, 6 h, and 48 h after exercise. Muscle GLUT-4 content after exercise was twofold higher (P < 0.05) in the trained than in the untrained state (10.7 +/- 1.2 and 4.7 +/- 0.7 optical density units, respectively) and was correlated with muscle glycogen concentration 6 h after exercise (r = 0.64, P < 0.05). Total glycogen synthase activity and the percentage of glycogen synthase I were not significantly different before and after training at 15 min, 6 h, and 48 h after exercise. We conclude that endurance exercise training enhances the capacity of human skeletal muscle to accumulate glycogen after glycogen-depleting exercise.     

Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance.

To test the effects of tyrosine ingestion with or without carbohydrate supplementation on endurance performance, nine competitive cyclists cycled at 70% peak oxygen uptake for 90 min under four different feeding conditions followed immediately by a time trial. At 30-min intervals, beginning 60 min before exercise, each subject consumed either 5 ml/kg body wt of water sweetened with aspartame [placebo (Pla)], polydextrose (70 g/l) (CHO), L-tyrosine (25 mg/kg body wt) (Tyr), or polydextrose (70 g/l) and L-tyrosine (25 mg/kg body wt) (CHO+Tyr). The experimental trials were given in random order and were carried out by using a counterbalanced double-blind design. No differences were found between treatments for oxygen uptake, heart rate, or rating of perceived exertion at any time during the 90-min ride. Plasma tyrosine rose significantly from 60 min before exercise to test termination (TT) in Tyr (means +/- SE) (480 +/- 26 micromol) and CHO+Tyr (463 +/- 34 micromol) and was significantly higher in these groups from 30 min before exercise to TT vs. CHO (90 +/- 3 micromol) and Pla (111 +/- 7 micromol) (P < 0.05). Plasma free tryptophan was higher after 90 min of exercise, 15 min into the endurance time trial, and at TT in Tyr (10.1 +/- 0.9, 10.4 +/- 0.8, and 12.0 +/- 0.9 micromol, respectively) and Pla (9.7 +/- 0.5, 10.0 +/- 0.3, and 11.7 +/- 0.5 micromol, respectively) vs. CHO (7.8 +/- 0.5, 8.6 +/- 0.5, and 9.3 +/- 0.6 micromol, respectively) and CHO+Tyr (7.8 +/- 0.5, 8.5 +/- 0.5, 9.4 +/- 0.5 micromol, respectively) (P < 0.05). The plasma tyrosine-to-free tryptophan ratio was significantly higher in Tyr and CHO+Tyr vs. CHO and Pla from 30 min before exercise to TT (P < 0.05). CHO (27.1 +/- 0.9 min) and CHO+Tyr (26.1 +/- 1.1 min) treatments resulted in a reduced time to complete the endurance time trial compared with Pla (34.4 +/- 2.9 min) and Tyr (32.6 +/- 3.0 min) (P < 0.05). These findings demonstrate that tyrosine ingestion did not enhance performance during a cycling time trial after 90 min of steady-state exercise.     

Effect of cocaine on exercise endurance and glycogen use in rats

To determine the effects of cocaine on exercise endurance, male rats were injected intraperitoneally with cocaine (20 mg/kg body wt) or saline and then run to exhaustion 20 min later at 22 m/min and 15% grade. Saline-injected animals ran 74.9 +/- 16.5 (SD) min, whereas cocaine-treated rats ran only 29 +/- 11.6 min. The drug had no effect on resting blood glucose or lactate levels, nor did it affect resting glycogen levels in liver or red and white vastus muscle. However, it did reduce resting soleus glycogen content by 30%. During exercise liver and soleus glycogen depletion occurred at the same rate in saline- and cocaine-treated animals. In contrast, the rate of glycogen depletion during exercise in red and white vastus was markedly increased in cocaine-treated rats with a corresponding elevation in blood lactate (12 vs. only 5 mM in saline group) at exhaustion. These data suggest that cocaine administration (20 mg/kg) before submaximal exercise dramatically alters glycogen metabolism during exercise, and this effect has a negative impact on exercise endurance.     

Effect of endurance exercise training on muscle glycogen supercompensation in rats

Nakatani, Akira, Dong-Ho Han, Polly A. Hansen, Lorraine A. Nolte, Helen H. Host, Robert C. Hickner, and John O. Holloszy. Effect of endurance exercise training on muscle glycogensupercompensation in rats. J. Appl.Physiol. 82(2): 711-715, 1997.The purpose of this study was to test the hypothesis that the rate and extent ofglycogen supercompensation in skeletal muscle are increased byendurance exercise training. Rats were trained by using a 5-wk-long swimming program in which the duration of swimming was gradually increased to 6 h/day over 3 wk and then maintained at 6 h/day for anadditional 2 wk. Glycogen repletion was measured in trained anduntrained rats after a glycogen-depleting bout of exercise. The ratswere given a rodent chow diet plus 5% sucrose in their drinking waterad libitum during the recovery period. There were remarkabledifferences in both the rates of glycogen accumulation and the glycogenconcentrations attained in the two groups. The concentration ofglycogen in epitrochlearis muscle averaged 13.1 ± 0.9 mg/g wet wtin the untrained group and 31.7 ± 2.7 mg/g in the trained group(P < 0.001) 24 h after the exercise.This difference could not be explained by a training effect on glycogensynthase. The training induced ~50% increases in muscle GLUT-4glucose transporter protein and in hexokinase activity inepitrochlearis muscles. We conclude that endurance exercise trainingresults in increases in both the rate and magnitude of muscle glycogensupercompensation in rats.

     

Muscle glycogen accumulation after endurance exercise in trained and untrained individuals

Hickner, R. C., J. S. Fisher, P. A. Hansen, S. B. Racette,C. M. Mier, M. J. Turner, and J. O. Holloszy. Muscle glycogen accumulation after endurance exercise in trained and untrained individuals. J. Appl. Physiol. 83(3):897-903, 1997.Muscle glycogen accumulation was determined in sixtrained cyclists (Trn) and six untrained subjects (UT) at 6 and either48 or 72 h after 2 h of cycling exercise at ~75% peakO₂ uptake(O_{2 peak}), which terminated with five 1-min sprints. Subjects ate 10 gcarbohydrate · kg¹ · day¹for 48-72 h postexercise. Muscle glycogen accumulation averaged 71 ± 9 (SE) mmol/kg (Trn) and 31 ± 9 mmol/kg (UT) during the first 6 h postexercise (P < 0.01) and 79 ± 22 mmol/kg (Trn) and 60 ± 9 mmol/kg (UT) between 6 and 48 or 72 h postexercise (not significant). Muscle glycogenconcentration was 164 ± 21 mmol/kg (Trn) and 99 ± 16 mmol/kg(UT) 48-72 h postexercise (P < 0.05). Muscle GLUT-4 content immediately postexercise was threefoldhigher in Trn than in UT (P < 0.05)and correlated with glycogen accumulation rates (r = 0.66, P < 0.05). Glycogen synthase in theactive I form was 2.5 ± 0.5, 3.3 ± 0.5, and 1.0 ± 0.3 µmol · g¹ · min¹in Trn at 0, 6, and 48 or 72 h postexercise, respectively;corresponding values were 1.2 ± 0.3, 2.7 ± 0.5, and 1.6 ± 0.3 µmol · g¹ · min¹in UT (P < 0.05 at 0 h). Plasmainsulin and plasma C-peptide area under the curve were lower in Trnthan in UT over the first 6 h postexercise(P < 0.05). Plasma creatine kinaseconcentrations were 125 ± 25 IU/l (Trn) and 91 ± 9 IU/l (UT)preexercise and 112 ± 14 IU/l (Trn) and 144 ± 22 IU/l(UT; P < 0.05 vs.preexercise) at 48-72 h postexercise (normal: 30-200 IU/l).We conclude that endurance exercise training results in an increasedability to accumulate muscle glycogen after exercise.

     

Relative effects of glycogen depletion and previous exercise on muscle force and endurance capacity

Endurance capacity of human vastus lateralis muscles was observed 24 h after hard exercise followed by either a carbohydrate-restricted or a carbohydrate-loaded diet (depletion and repletion conditions). In a control condition the subjects did no previous exercise and ate their normal diet. Each of these conditions was followed by an experimental protocol in which the five male subjects made a series of alternating 25-s static contractions of each leg at 50% maximal voluntary contraction until one leg failed to achieve the required force (Tlim). Glycogen concentration before the experimental protocol in both legs was significantly lower in the depletion than in the repletion condition. Muscle lactate and creatine phosphate concentrations were within normal limits before the static contractions. The number of contractions the repleted (12.7 +/- 2.2) and depleted (10.3 +/- 1.5) legs could sustain before Tlim were not different from each other, but both were 35% (P less than 0.05) fewer than the control (17.6 +/- 3.0). Surface electromyogram (EMG) amplitude was higher in depleted than in repleted or control muscles. At Tlim, EMG amplitude was maximal, creatine phosphate was 50-70% depleted, and lactate increased fourfold. Average glycogen utilization per contraction in both the repletion and depletion conditions was 5.8 mmol/kg dry wt, but postexercise lactate concentrations were lower in depleted (14.4 +/- 3.6 mmol/kg dry wt) than in repleted (43.2 +/- 7.4) muscles. The EMG frequency distribution shifted downward in all conditions during the experimental protocol and was independent of muscle lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of carbohydrate dosage on exercise performance and glycogen metabolism

This study was undertaken to examine the effects of ingestion of carbohydrate (CHO) solutions of 0 (WP), 6 (CHO-6), 12 (CHO-12), and 18 g CHO/100 ml (CHO-18) on performance and muscle glycogen use. Ten trained cyclists performed five 120-min cycling trials. The first 105 min of each trial was at 70% of maximal O2 consumption (VO2max), and the final 15 min was an all-out performance ride on an isokinetic cycle ergometer equipped to measure total work output. In one of the trials (CHO-12I) the submaximal portion of the ride consisted of seven 15-min rides at 70% of VO2max with a 3-min rest between each ride. Every 15 min the men consumed 8.5 ml.kg-1.h-1 (approximately 150 ml) of one of the four test solutions. Venous blood samples were obtained every 15 min for glucose and insulin. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen and sectioned and stained for myosin adenosinetriphosphatase and glycogen for single fiber depletion measurements. There were no differences in glycogen use (86.7 +/- 6.0, 75.5 +/- 7.9, and 83.5 +/- 5.5 mmol/kg for the WP, CHO-12C, and CHO-12I, respectively) or depletion patterns between the WP and the two CHO-12 trials. Blood glucose was significantly elevated in both the CHO-12 trials and in the CHO-18 trial compared with the WP trial.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of aerobic exercise on strength performance following various periods of recovery

The purpose of this study was to determine if the type and intensity of aerobic training affects performance in a subsequent strength-training session after varying periods of recovery. Sixteen male subjects participated in the study and were divided into 2 groups based on aerobic training, high-intensity intervals (MAX n = 8) and continuous submaximal (SUB n = 8). Each subject performed 4 sets of both bench press and leg press at approximately 75% 1 repetition maximum (1RM) following aerobic training with recovery periods of 4, 8, and 24 hours, as well as once in a control condition. Both the 4- and 8-hour conditions resulted in fewer total leg press repetitions than the control and 24-hour conditions. There was no difference between both the control and 24-hour conditions. No main effect was shown with respect to the type of aerobic training. It was concluded that when aerobic training precedes strength training, the volume of work that can be performed is diminished for up to 8 hours. This impairment appears to be localized to the muscle groups involved in the aerobic training.     

Effects of preexercise snack feeding on endurance cycle exercise

We studied the effects of ingesting either a snack food (S) (260 kcal) or placebo (P) 30 min before intermittent cycle exercise at 70% maximal O2 consumption on endurance performance and muscle glycogen depletion in eight healthy human males. Immediately before exercise there were significantly greater increases in plasma glucose (PG) (S +28 +/- 9.7; P +0.1 +/- 0.8 mg/dl) and insulin (S +219 +/- 61.5; P -7 +/- 5.5 pmol/l) (P less than 0.05) following S feeding compared with P. These differences were no longer present by the end of the first exercise period. There were no differences in endurance times (S 52 +/- 6.4; P 48 +/- 5.6 min) or in the extent of muscle glycogen depletion following exercise (S 56 +/- 14.7; P 50 +/- 15.5 micrograms/mg protein) between the two groups. PG was maintained at base-line (prefeeding) concentrations following S, whereas there was a tendency for PG to steadily decrease after P. Total grams of carbohydrate oxidized during exercise did not differ between the two groups (S 120; P 118 g). These results demonstrate that the ingestion of a mixed-macronutrient snack 30 min before exercise does not impair endurance performance nor increase the extent of muscle glycogen depletion during high-intensity cycle exercise in untrained adult male subjects.     

Effect of ginger extract ingestion on skeletal muscle glycogen contents and endurance exercise in male rats

[Purpose]Skeletal muscle glycogen is a determinant of endurance capacity for some athletes. Ginger is well known to possess nutritional effects, such as anti-diabetic effects. We hypothesized that ginger extract (GE) ingestion increases skeletal muscle glycogen by enhancing fat oxidation. Thus, we investigated the effect of GE ingestion on exercise capacity, skeletal muscle glycogen, and certain blood metabolites in exercised rats. [Methods]First, we evaluated the influence of GE ingestion on body weight and elevation of exercise performance in rats fed with different volumes of GE. Next, we measured the skeletal muscle glycogen content and free fatty acid (FFA) levels in GE-fed rats. Finally, we demonstrated that GE ingestion contributes to endurance capacity during intermittent exercise to exhaustion. [Results]We confirmed that GE ingestion increased exercise performance (p<0.05) and elevated the skeletal muscle glycogen content compared to the non-GE-fed (CE, control exercise) group before exercise (Soleus: p<0.01, Plantaris: p<0.01, Gastrocnemius: p<0.05). Blood FFA levels in the GE group were significantly higher than those in the CE group after exercise (p<0.05). Moreover, we demonstrated that exercise capacity was maintained in the CE group during intermittent exercise (p<0.05). [Conclusion]These findings indicate that GE ingestion increases skeletal muscle glycogen content and exercise performance through the upregulation of fat oxidation.     

Effects of age and regular exercise on muscle strength and endurance

Twenty male and 20 female non-professional tennis players were classified into two different age groups (n = 10 per group): young active men (30.4 +/- 3.3 years), young active women (27.5 +/- 4.3 years), elderly active men (64.4 +/- 3.7 years), and elderly active women (65.3 +/- 4.5 years). These individuals were matched (n = 10 per group) according to sex, age, height and mass to sedentary individuals of the same socio-economical background: young sedentary men (29.2 +/- 3.4 years), young sedentary women (25.6 +/- 4.4 years), elderly sedentary men (65.2 +/- 3.2 years) and elderly sedentary women (65.6 +/- 4.4 years). An isokinetic dynamometer was used to measure the strength of the knee extensors and flexors (two separate occasions) and the endurance of the extensors. Vastus lateralis electromyogram (EMG) was measured concomitantly. Significant sex, age and exercise effects (P less than 0.001) were observed for peak torque of both muscle groups. The effect of age on extensor strength was more pronounced at high speeds where men were also able to generate larger relative torques than women. No age or sex effects were noted for muscle endurance. However, muscles of active individuals demonstrated a greater resistance to fatigue than those of sedentary individuals. In conclusion, men were found to be stronger than women, age was associated with a decrease in muscle strength, but not of muscle endurance, and tennis players were stronger and had muscles that were more resistant to fatigue than their sedentary pairs in both age groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of postexercise carbohydrate-protein feedings on muscle glycogen restoration.

The purpose of this investigation was to determine the effects of postexercise eucaloric carbohydrate-protein feedings on muscle glycogen restoration after an exhaustive cycle ergometer exercise bout. Seven male collegiate cyclists [age = 25.6 +/- 1.3 yr, height = 180.9 +/- 3.2 cm, wt = 75.4 +/- 4.0 kg, peak oxygen uptake (VO(2 peak)) = 4.20 +/- 0.2 l/min] performed three trials, each separated by 1 wk: 1) 100% alpha-D-glucose [carbohydrate (CHO)], 2) 70% carbohydrate-20% protein (PRO)-10% fat, and 3) 86% carbohydrate-14% amino acid (AA). All feedings were eucaloric, based on 1.0 g. kg body wt(-1). h(-1) of CHO, and administered every 30 min during a 4-h muscle glycogen restoration period in an 18% wt/vol solution. Muscle biopsies were obtained immediately and 4 h after exercise. Blood samples were drawn immediately after the exercise bout and every 0.5 h for 4 h during the restoration period. Increases in muscle glycogen concentrations for the three feedings (CHO, CHO-PRO, CHO-AA) were 118 mmol/kg dry wt; however, no differences among the feedings were apparent. The serum glucose and insulin responses did not differ throughout the restoration period among the three feedings. These results suggest that muscle glycogen restoration does not appear to be enhanced with the addition of proteins or amino acids to an eucaloric CHO feeding after exhaustive cycle exercise.     

Effects of diet on muscle triglyceride and endurance performance

Starling, Raymond D., Todd A. Trappe, Allen C. Parcell, ChadG. Kerr, William J. Fink, and David L. Costill. Effects of diet onmuscle triglyceride and endurance performance. J. Appl. Physiol. 82(4): 1185-1189, 1997.Thepurpose of this investigation was to examine the effects of diet onmuscle triglyceride and endurance performance. Seven endurance-trainedmen completed a 120-min cycling bout at 65% of maximal oxygen uptake.Each subject then ingested an isocaloric high-carbohydrate (Hi-CHO;83% of energy) or a high-fat (Hi-Fat; 68% of energy) diet for theensuing 12 h. After a 12-h overnight fast, a 1,600-kJ self-pacedcycling bout was completed. Muscle triglyceride measured before (33.0 ± 2.3 vs. 37.0 ± 2.1 mmol/kg dry wt) and after (30.9 ± 2.4 vs. 32.8 ± 1.6 mmol/kg dry wt) the 120-min cycling bout was notdifferent between the Hi-CHO and Hi-Fat trials, respectively. After the 24-h dietary-fasting period, muscle triglyceride was significantly higher for the Hi-Fat (44.7 ± 2.4 mmol/kg dry wt) vs. the Hi-CHO (27.5 ± 2.1 mmol/kg dry wt) trial. Furthermore,self-paced cycling time was significantly greater for the Hi-Fat (139.3 ± 7.1 min) compared with the Hi-CHO (117.1 ± 3.2 min) trial.These data demonstrate that there was not a significant difference inmuscle triglyceride concentration before and after a prolongedmoderate-intensity cycling bout. Nevertheless, a high-fat dietincreased muscle triglyceride concentration and reduced self-pacedcycling performance 24 h after the exercise compared with ahigh-carbohydrate diet.