challenge. A formulated carbohydrate supplement gel disk containing 30 g of carbohydrates (2∶1 glucose∶fructose) with accompanying temperate water (10% w/v; 316 mOsmol/kg; ∼20 °C water temperature) was ingested at 0 min and every 20 min, thereafter until the completion of the 2-hr steady-state running
Stephanie K. Gaskell, Rhiannon M.J. Snipe and Ricardo J.S. Costa
Guihua Zhang, Nobuya Shirai and Hiramitsu Suzuki
The aim of this study was to investigate the effect of L-lactic acid on swimming endurance of mice. Mice (n = 50) were injected intraperitoneally with saline, then with L-lactic acid (either 25 mg/kg or 50 mg/kg body weight), then after 2 days with the same doses of glucose, and after another 2 days again with L-lactic acid at the same doses. Swimming times to exhaustion were determined at 30 min after each injection, in a tank filled with 25 cm of water maintained at 23 °C. After another week, mice were given either saline, L-lactic acid, or glucose (25 or 50 mg/kg) dissolved in saline and sacrificed after 30 min for biochemical analyses. The ratios of swimming times of L-lactic acid or glucose injections to saline injection were calculated as an index for endurance changes. Swimmingtime ratios for mice injected with L-lactic acid were significantly higher at either dose than for those injected with the corresponding doses of glucose (p < .05). The ratio of swimming time was greater in those given a dose of 50 mg/kg than in those given 25 mg/kg for mice in the L-lactic acid groups (p < .05) but not in the groups given glucose. There were no marked differences in biochemical parameters of plasma and muscle lactate, muscle and liver glycogen, or plasma glucose and nonesterified fatty acid between the L-lactic acid, glucose, and saline injection groups. These results suggest that L-lactic acid can enhance swimming endurance of mice and that this action is dose dependent.
Michael S. Green, J. Andrew Doyle, Christopher P. Ingalls, Dan Benardot, Jeffrey C. Rupp and Benjamin T. Corona
This study determined whether disrupted glucose and insulin responses to an oral glucose-tolerance test (OGTT) induced by eccentric exercise were attenuated after a repeated bout. Female participants (n = 10, age 24.7 ± 3.0 yr, body mass 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29% ± 2%) performed 2 bouts of downhill running (DTR 1 and DTR 2) separated by 14 d. OGTTs were administered at baseline and 48 hr after DTR 1 and DTR 2. Maximum voluntary isometric quadriceps torque (MVC), subjective soreness (100-mm visual analog scale), and serum creatine kinase (CK) were assessed pre-, post-, and 48 hr post-DTR 1 and DTR 2. Insulin and glucose area under the curve (38% ± 8% and 21% ± 5% increase, respectively) and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 μU/ml) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol/L) were elevated after DTR 1, with no increase above baseline 48 hr after DTR 2. MVC remained reduced by 9% ± 3% 48 hr after DTR 1, recovering back to baseline 48 hr after DTR 2. Soreness was elevated to a greater degree 48 hr after DTR 1 (48 ± 6 vs. 13 ± 3 mm), with a tendency for greater CK responses 48 hr after DTR 1 (813 ± 365 vs. 163 ± 43 U/L, p = .08). A novel bout of eccentric exercise confers protective effects, with subsequent bouts failing to elicit disruptions in glucose and insulin homeostasis.
Kelsey H. Fisher-Wellman and Richard J. Bloomer
Carbohydrate powder in the form of maltodextrin is widely used by athletes for postexercise glycogen resynthesis. There is some concern that such a practice may be associated with a postprandial rise in reactive oxygen and nitrogen species production and subsequent oxidation of macromolecules. This is largely supported by findings of increased oxidative-stress biomarkers and associated endothelial dysfunction after intake of dextrose.
To compare the effects of isocaloric dextrose and maltodextrin meals on blood glucose, triglycerides (TAG), and oxidative-stress biomarkers in a sample of young healthy men.
10 men consumed isocaloric dextrose and maltodextrin powder drinks (2.25 g/kg) in a random-order, crossover design. Blood samples were collected premeal (fasting) and at 1, 2, 4, and 6 hr postmeal and assayed for glucose, TAG, malondialdehyde, hydrogen peroxide, nitrate/nitrite, and Trolox-equivalent antioxidant capacity.
Significant meal effects were noted for glucose total area under the curve (p = .004), with values higher for the dextrose meal. No other statistically significant meal effects were noted (p > .05). With respect to the 2 (meal) × 5 (time) ANOVA, no significant interaction, time, or meal effects were noted for any variable (p > .05), with the exception of glucose, for which a main effect for both meal (p < .0001) and time (p = .0002) was noted.
These data indicate that carbohydrate meals, consumed as either dextrose or maltodextrin, pose little postprandial oxidative insult to young, healthy men. As such, there should be minimal concern over such feedings, even at high dosages, assuming adequate glucose metabolism.
William A. Burgess, J. Mark Davis, William P. Bartoli and Jeffrey A. Woods
The effects of ingesting a low dose of CHO on plasma glucose, glucoregulatory hormone responses, and performance during prolonged cycling were investigated. Nine male subjects cycled for 165 min at ≈67% peak
Owen Spendiff and Ian G. Campbell
Seven athletes with low lesion paraplegia ingested a 7.6% 648ml glucose drink using two schedules of ingestion (4 × 162 ml per 20 min & 2 × 324 ml per 60 min) in a crossover design. Participants exercised at 65% peak oxygen uptake for one hour, followed by a 20-minute performance test. The cardiorespiratory responses during the one-hour tests were similar between trials. Plasma glucose concentrations significantly increased after ingestion and remained stable during the 162 trial, but reduced over time during the 324 trial. Free fatty acid concentrations increased for both trials but increased significantly more during the 324 trial. The results of this study suggest that the ingestion of glucose during exercise is the best strategy for wheelchair athletes competing in endurance events.
Darlene A. Sedlock, Man-Gyoon Lee, Michael G. Flynn, Kyung-Shin Park and Gary H. Kamimori
Literature examining the effects of aerobic exercise training on excess postexercise oxygen consumption (EPOC) is sparse. In this study, 9 male participants (19–32 yr) trained (EX) for 12 wk, and 10 in a control group (CON) maintained normal activity. VO2max, rectal temperature (Tre), epinephrine, norepinephrine, free fatty acids (FFA), insulin, glucose, blood lactate (BLA), and EPOC were measured before (PRE) and after (POST) the intervention. EPOC at PRE was measured for 120 min after 30 min of treadmill running at 70% VO2max. EX completed 2 EPOC trials at POST, i.e., at the same absolute (ABS) and relative (REL) intensity; 1 EPOC test for CON served as both the ABS and REL trial because no significant change in VO2max was noted. During the ABS trial, total EPOC decreased significantly (p < .01) from PRE (39.4 ± 3.6 kcal) to POST (31.7 ± 2.2 kcal). Tre, epinephrine, insulin, glucose, and BLA at end-exercise or during recovery were significantly lower and FFA significantly higher after training. Training did not significantly affect EPOC during the REL trial; however, epinephrine was significantly lower, and norepinephrine and FFA, significantly higher, at endexercise after training. Results indicate that EPOC varies as a function of relative rather than absolute metabolic stress and that training improves the efficiency of metabolic regulation during recovery from exercise. Mechanisms for the decreased magnitude of EPOC in the ABS trial include decreases in BLA, Tre, and perhaps epinephrine-mediated hepatic glucose production and insulin-mediated glucose uptake.
Kevin J. Cole, Peter W. Grandjean, Richard J. Sobszak and Joel B. Mitchell
This study examined the effects of serial feedings of different carbohydrate (CHO) solutions on plasma volume, gastric emptying (GE), and performance during prolonged cycling exercise. Solutions containing 6 g% glucose-sucrose (CHO-6GS), 83 g% high fructose com syrup (CHO-8HF), 6.3 g% high fructose corn syrup + 2 g% glucose polymer (CHO-8HP), and a water placebo (WP) were compared. Ten trained male cyclists performed four cycling trials consisting of 105 min at 70% VQ2max followed by a 15-min all-out, self-paced performance ride. Every 15 min the men consumed one of the four test solutions. Blood samples were taken before, during, and after exercise to determine blood glucose and plasma volume changes. There were no significant differences in performance, GE, or plasma volume changes between trials. Blood glucose was significantly elevated at the 105-min timepoint in all CHO trials when compared to WP. The CHO-8HF and CHO-8HP drinks resulted in a significantly higher delivery of CHO to the intestine. Higher rates of CHO oxidation during the steady-state ride were observed only with the CHO-6GS drink.
Mahmoud S. El-Sayed, Angelheart J.M. Rattu and Ian Roberts
The study examined the effect of carbohydrate ingestion on exercise performance capacity. Nine male cyclists performed two separate trials at 70%
Joel B. Mitchell, Paul C. DiLauro, Francis X. Pizza and Daniel L. Cavender
The purpose of this study was to determine the effect of a high vs. a low preexercise carbohydrate (CHO) diet on performance during multiple sets of resistance exercise. Eleven resistance-trained males performed cycle ergometry to deplete quadriceps muscle glycogen stores, followed by 48 hr of a high (HICHO) or a low (LOCHO) CHO diet. Subjects then performed five sets each of squats, leg presses, and knee extensions (resistance = 15 RM) to failure. Blood samples were taken before and during exercise for determination of glucose and lactate (LA). No differences in performance (repetitions X weight lifted) were observed (HICHO = 15,975±1,381 and LOCHO = 15,723±1,231 kg). Blood glucose was significantly higher after exercise for HICHO compared to LOCHO (HICHO = 4.8 ± 0.2 vs. LOCHO = 3.9 ± 0.2 mmol·L−1). No differences in LA accumulation were observed. The data indicated that preexercise CHO status did not affect resistance exercise performance. Further, the differences in blood glucose and the similarity in LA responses suggest that glycolysis was maintained in the LOCHO condition, and there may have been an increased reliance on blood glucose when preexercise CHO status was low.