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The present study was designed to assess the impact of coingestion of various amounts of carbohydrate combined with an ample amount of protein intake on postexercise muscle protein synthesis rates. Ten healthy, fit men (20 [+ or -] 0.3 yr) were randomly assigned to three crossover experiments. After 60 min of resistance exercise, subjects consumed 0.3 g*[kg.sup.-1]*[h.sup.-1] protein hydrolysate with 0, 0.15, or 0.6 g*[kg.sup.-1]*[h.sup.-1] carbohydrate during a 6-h recovery period (PRO, PRO + LCHO, and PRO + HCHO, respectively). Primed, continuous infusions with L-[[ring-.sup.13][C.sub.6]]phenylalanine, L-[[ring-.sup.2][H.sub.2]]tyrosine, and [6,6-[sup.2][H.sub.2]]glucose were applied, and blood and muscle samples were collected to assess whole body protein turnover and glucose kinetics as well as protein fractional synthesis rate (FSR) in the vastus lateralis muscle over 6 h of postexercise recovery. Plasma insulin responses were significantly greater in PRO + HCHO compared with PRO + LCHO and PRO (18.4 [+ or -] 2.9 vs. 3.7 [+ or -] 0.5 and 1.5 [+ or -] 0.2 U*6 [h.sup.1]*[1.sup.-1], respectively, P < 0.001). Plasma glucose rate of appearance ([R.sub.a]) and disappearance (Ra) increased over time in PRO + HCHO and PRO + LCHO, but not in PRO. Plasma glucose [R.sub.a] and [R.sub.d] were substantially greater in PRO + HCHO vs. both PRO and PRO + LCHO (P < 0.01). Whole body protein breakdown, synthesis, and oxidation rates, as well as whole body protein balance, did not differ between experiments. Mixed muscle protein FSR did not differ between treatments and averaged 0.10 [+ or -] 0.01, 0.10 [+ or -] 0.01, and 0.11 [+ or -] 0.01%/h in the PRO, PRO + LCHO, and PRO + HCHO experiments, respectively. In conclusion, coingestion of carbohydrate during recovery does not further stimulate postexercise muscle protein synthesis when ample protein is ingested. resistance exercise; protein metabolism; nutrition; recovery

Intramyocellular triacylglycerol (IMTG) has been suggested to represent an important substrate source during exercise. In the present study, IMTG utilization during exercise is assessed through the use of various methodologies. In addition, we identified differences in the use of intramyocellular lipids deposited in the immediate subsarcolemmal (SS) area and those stored in the more central region of the fiber. Contemporary stable isotope technology was applied in combination with muscle tissue sampling before and immediately after 3 h of moderate-intensity cycling exercise (62 [+ or -] 2% V[O.sub.2max]) in eight well-trained male cyclists. Continuous infusions with [U-[sup.13]C]palmitate and [6,6-[sup.2][H.sub.2]]glucose were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate whole body IMTG and glycogen use. Both immunohisto-chemical analyses of oil red O (ORO)-stained muscle cross sections and biochemical triacylglycerol (TG) extraction were performed to assess muscle lipid content. During exercise, plasma FFA, muscle (and/or lipoprotein)-derived TG, plasma glucose, and muscle glycogen oxidation contributed 24 [+ or -] 2, 22 [+ or -] 3, 11 [+ or -] 1, and 43 [+ or -] 3% to total energy expenditure, respectively. In accordance, a significant net decline in muscle lipid content was observed following exercise as assessed by ORO staining (67 [+ or -] 8%) and biochemical TG extraction (49 [+ or -] 8%), and a positive correlation was observed between methods (r = 0.56; P < 0.05). Lipid depots located in the SS area were utilized to a greater extent than the more centrally located depots. This is the first study to show significant use of IMTG as a substrate source during exercise in healthy males via the concurrent implementation of three major methodologies. In addition, this study shows differences in resting subcellular intramyocellular lipid deposit distribution and in the subsequent net use of these deposits during exercise. fat metabolism; intramyocellular triacylglycerol; skeletal muscle; cycling; substrate utilization doi:10.1152/ajpendo.00678.2006.

Five days of a high-fat diet while training, followed by 1 day of carbohydrate (CHO) restoration, increases rates of whole body fat oxidation and decreases CHO oxidation during aerobic cycling. The mechanisms responsible for these shifts in fuel oxidation are unknown but involve up- and downregulation of key regulatory enzymes in the pathways of skeletal muscle fat and CHO metabolism, respectively. This study measured muscle PDH and HSL activities before and after 20 min of cycling at 70% V[O.sub.2 peak] and 1 min of sprinting at 150% peak power output (PPO). Estimations of muscle glycogenolysis were made during the initial minute of exercise at 70% V[O.sub.2 peak] and during the 1-min sprint. Seven male cyclists undertook this exercise protocol on two occasions. For 5 days, subjects consumed in random order either a high-CHO (HCHO) diet (10.3 g*[kg.sup.-1]*[day.sup.-1] CHO, or ~70% of total energy intake) or an isoenergetic high-fat (FAT-adapt) diet (4.6 g*[kg.sup.-]*[day.sup.-1] FAT, or 67% of total energy) while undertaking supervised aerobic endurance training. On day 6 for both treatments, subjects ingested an HCHO diet and rested before their experimental trials on day 7. This CHO restoration resulted in similar resting glycogen contents (FAT-adapt 873 [+ or -] 121 vs. HCHO 868 [+ or -] 120 [micro]mol glucosyl units/g dry wt). However, the respiratory exchange ratio was lower during cycling at 70% V[O.sub.2 peak] in the FAT-adapt trial, which resulted in an ~45% increase and an ~30% decrease in fat and CHO oxidation, respectively. PDH activity was lower at rest and throughout exercise at 70% V[O.sub.2 peak] (1.69 [+ or -] 0.25 vs. 2.39 [+ or -] 0.19 mmol*kg wet [wt.sup.-1]*[min.sup.-1]) and the 1-min sprint in the FAT-adapt vs. the HCHO trial. Estimates of glycogenolysis during the 1st min of exercise at 70% V[O.sub.2 peak] and the 1-min sprint were also lower after FAT-adapt (9.1 [+ or -] 1.1 vs. 13.4 [+ or -] 2.1 and 37.3 [+ or -] 5.1 vs. 50.5 [+ or -] 2.7 glucosyl units*kg dry [wt.sup.-l]*[min.sup.-1]). HSL activity was ~20% higher (P = 0.12) during exercise at 70% V[O.sub.2 peak] after FAT-adapt. Results indicate that previously reported decreases in whole body CHO oxidation and increases in fat oxidation after the FAT-adapt protocol are a function of metabolic changes within skeletal muscle. The metabolic signals responsible for the shift in muscle substrate use during cycling at 70% V[O.sub.2 peak] remain unclear, but lower accumulation of free ADP and AMP after the FAT-adapt trial may be responsible for the decreased glycogenolysis and PDH activation during sprinting. skeletal muscle metabolism; pyruvate dehydrogenase; substrate phosphorylation; fat oxidation; carbohydrate oxidation

This study investigated the effect of reduced free fatty acid (FFA) availability on pyruvate dehydrogenase activation (PDHa) and carbohydrate metabolism during moderate aerobic exercise. Eight active male subjects cycled for 40 min at 55% V[O.sub.2peak] on two occasion. During one trial, subjects ingested 20 mg/kg body mass of the antilipolytic drug nicotinic acid (NA) during the hour before exercise to reduce FFA. Nothing was ingested in the control trial (CON). Blood and expired gas measurements were obtained throughout the trials, and muscle biopsy samples were obtained immediately before exercise and at 5, 20, and 40 min of exercise. Plasma FFA were lower in the NA trial (0.13 [+ or -] 0.01 vs. 0.48 [+ or -] 0.03 mM, P < 0.05), and the respiratory exchange ratio (RER) was increased with NA (0.93 [+ or -] 0.01 vs. 0.89 [+ or -] 0.01, P < 0.05), resulting in a 14.5 [+ or -] 1.8% increase in carbohydrate oxidation compared with CON. PDHa increased rapidly in both trials at exercise onset but was ~15% higher (P < 0.05) throughout exercise in the NA trial (2.44 [+ or -] 0.19 and 2.07 [+ or -] 0.12 mmol*kg wet [muscle.sup.-1]*[min.sup.-1] for NA and CON at 40 min). Muscle glycogenolysis was 15.3 [+ or -] 9.6% greater in the NA trial vs. the CON trial but did not reach statistical significance. Glucose 6-phosphate contents were elevated (P < 0.05) in the NA trial at 30 and 40 min of exercise, but pyruvate and lactate contents were unaffected. These data demonstrate that the reduction of exogenous FFA availability increased the activation of PDH and carbohydrate oxidation during moderate aerobic exercise in men. The increased activation of PDH was not explained by changes in muscle pyruvate or the ATP/ ADP ratio but may be related to a decrease in the NADH/ NA[D.sup.+] ratio or an epinephrine-induced increase in calcium concentration. pyruvate dehydrogenase activity; nicotinic acid; carbohydrate and fat oxidation

A study was conducted to investigate whether the supplement Microhydrin (MH) contains silica hydride bonds (Si-H) and whether Microhydrin supplementation increased performance or altered metabolism compared to placebo (PL) during prolonged endurance cycling. The results indicated that oral Microhydrin supplementation did not enhance cycling time trial performance or alter metabolism during prolonged submaximal exercise in endurance-trained cyclists.