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Kevin R. Short, April M. Teague, Jake C. Klein, Elizabeth Malm-Buatsi and Dominic Frimberger

Purpose:

Whole body or leg exercise before a meal can increase insulin sensitivity, but it is unclear whether the same can occur with upper body exercise since a smaller muscle mass is activated. We measured the impact of a single session of handcycle exercise on glucose tolerance and insulin sensitivity.

Methods:

Nonambulatory (Non-Amb) adolescents with spina bifida or cerebral palsy (4F/3M), or ambulatory peers (Control, 4F/7M) completed 2 glucose tolerance tests on separate days, preceded by either rest or a 35-min bout of moderate-to-vigorous intermittent handcycle exercise.

Results:

The Non-Amb group had higher body fat (mean ± SD: 38 ± 12%, Control: 24 ± 9, p = .041) but similar VO2peak (17.7 ± 6.1 ml/kg/min, Control: 21.1 ± 7.9). Fasting glucose and insulin were normal for all participants. Compared with the rest trial, exercise resulted in a reduction in glucose area under the curve (11%, p = .008) without a significant group x trial interaction and no difference in the magnitude of change between groups. Insulin sensitivity was increased 16% (p = .028) by exercise in the Control group but was not significantly changed in the Non-Amb group.

Conclusion:

A single bout of handcycle exercise improves glucose tolerance in adolescents with and without mobility limitations and could therefore help maintain or improve metabolic health.

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Owen Spendiff and Ian G. Campbell

Eight men with spinal cord injury ingested glucose (CHO) or placebo (PLA) 20-min prior to exercise. Participants performed arm crank ergometry for one-hour at 65% V̇O2peak, followed by a 20-min performance test in which athletes were asked to achieve their greatest possible distance. Physiological responses during the one-hour tests were similar between CHO and PLA trials. At the onset of exercise, the CHO trial blood glucose concentrations were higher than PLA (p < .05) but returned to resting values after 20-min exercise. Respiratory exchange ratio responses during the CHO trial were indicative of a higher rate of CHO oxidation (p < .05). A greater distance (km) was covered in the 20-min performance tests after CHO ingestion (p < .05). Results show preingestion of glucose improves endurance performance of wheelchair athletes.

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Caitlin Campbell, Diana Prince, Marlia Braun, Elizabeth Applegate and Gretchen A. Casazza

Numerous studies have shown that ingesting carbohydrate in the form of a drink can improve exercise performance by maintaining blood glucose levels and sparing endogenous glycogen stores. The effectiveness of carbohydrate gels or jellybeans in improving endurance performance has not been examined. On 4 separate days and 1–2 hr after a standardized meal, 16 male (8; 35.8 ± 2.5 yr) and female (8; 32.4 ± 2.4 yr) athletes cycled at 75% VO2peak for 80 min followed by a 10-km time trial. Participants consumed isocaloric (0.6 g of carbohydrate per kg per hour) amounts of randomly assigned sports beans, sports drink, gel, or water only, before, during, and after exercise. Blood glucose concentrations were similar at rest between treatments and decreased significantly during exercise with the water trial only. Blood glucose concentrations for all carbohydrate supplements were significantly, p < .05, higher than water during the 80-min exercise bout and during the time trial (5.7 ± 0.2 mmol/L for sports beans, 5.6 ± 0.2 mmol/L for sports drink, 5.7 ± 0.3 mmol/L for gel, and 4.6 ± 0.3 mmol/L for water). There were no significant differences in blood glucose between carbohydrate treatments. The 10-km time trials using all 3 carbohydrate treatments were significantly faster (17.2 ± 0.6 min for sports beans, 17.3 ± 0.6 min for sports drink, and 17.3 ± 0.6 min for gel) than water (17.8 ± 0.7 min). All carbohydrate-supplement types were equally effective in maintaining blood glucose levels during exercise and improving exercise performance compared with water only.

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Bettina Mittendorfer and Samuel Klein

Endurance exercise increases the use of endogenous fuels to provide energy for working muscles. Elderly subjects oxidize more glucose and less fat during moderate intensity exercise. This shift in substrate use is presumably caused by age-related changes in skeletal muscle, including decreased skeletal muscle respiratory capacity, because adipose tissue lipolysis and plasma fatty acid availability are not rate limiting. Endurance training in elderly subjects increases muscle respiratory capacity, decreases glucose production and oxidation, and increases fat oxidation thereby correcting or compensating for the alterations in substrate oxidation associated with aging.

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Robert A. Robergs, Susie B. McMinn, Cristine Mermier, Guy Leadbetter III, Brent Ruby and Chris Quinn

This study was conducted to compare blood glucose and glucoregulatory hormone responses to the ingestion of solid and liquid carbohydrate (CHO) during prolonged cycling, followed by 30 min of isokinetic cycling. Eight male cyclists randomly completed three cycling trials (LC = liquid CHO, SCE = solid CHO with water equal to LC, SCA = solid CHO + ad libitum water). Each subject cycled for 120 min at 65% of VO2max with CHO ingestion (0.6 g CHO/kg/hr) at 0, 30, 60, 90, and 120 min. Subjects then completed a 30-min maximal isokinetic ride at 90 rpm. There was no significant (p < .05) difference between the trials for plasma glucose, insulin, glucagon, glycerol, lactate, RER, HR, VO2 RPE, and total work performed during the isokinetic ride. However, serum glucose was significantly lower in the SCE and SCA trials compared to LC at 80 min. The ingestion of a solid food containing CHO. protein, and fat with added water produced similar blood glucose, metabolic, glucoregulatory hormone, and exercise performance responses to those seen with the ingestion of liquid CHO.

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Stephen R. Stannard, Martin W. Thompson and Janette C. Brand Miller

Consumption of low glycemic index (GI) foods before submaximal endurance exercise may be beneficial to performance. To test whether this may also be true for high intensity exercise. 10 trained cyclists began an incremental exercise test to exhaustion 65 min after consuming equal carbohydrate portions of glucose (HGI), pasta (LGI), and a noncarbohydrate control (PL). Time to fatigue did not differ significantly (p = 0.05) between treatments. Plasma glucose concentration was significantly lower after LGI vs. HGI from 15 to 45 min of rest postprandial. During exercise, plasma glucose concentration was significantly lower after HGI vs. LGI from 200 W until exhaustion. Plasma lactate concentration following HGI was significantly higher than PL from 30 min of rest postprandial through to the end of the 200-W workload. Plasma lactate concentration following LGI was significantly lower than after HGI from 45 min of rest postprandial through to the end of the 100-W workload. At higher exercise intensities, there was no significant difference in plasma lactate levels between treatments. These findings suggest that a high GI carbohydrate meal (1 g/kg body wt) 65 min prior to exercise decreases plasma glucose and increases plasma lactate levels compared to a low GI meal, but not enough to be detrimental to incremental exercise performance.

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Matthew David Cook, Stephen David Myers, John Stephen Michael Kelly and Mark Elisabeth Theodorus Willems

Impaired glucose tolerance was shown to be present 48 hr following muscle-damaging eccentric exercise. We examined the acute effect of concentric and muscle-damaging eccentric exercise, matched for intensity, on the responses to a 2-hr 75-g oral glucose tolerance test (OGTT). Ten men (27 ± 9 years, 178 ± 7 cm, 75 ± 11 kg, VO2max: 52.3 ± 7.3 ml·kg-1·min-1) underwent three OGTTs after an overnight 12 hr fast: rest (control), 40-min (5 × 8-min with 2-min interbout rest) of concentric (level running, 0%, CON) or eccentric exercise (downhill running, –12%, ECC). Running intensity was matched at 60% of maximal metabolic equivalent. Maximal isometric force of m. quadriceps femoris of both legs was measured before and after the running protocols. Downhill running speed was higher (level: 9.7 ± 2.1, downhill: 13.8 ± 3.2 km·hr-1, p < .01). Running protocols had similar VO2max (p = .59), heart rates (p = .20) and respiratory exchange ratio values (p = .74) indicating matched intensity and metabolic demands. Downhill running resulted in higher isometric force deficits (level: 3.0 ± 6.7, downhill: 17.1 ± 7.3%, p < .01). During OGTTs, area-under-the-curve for plasma glucose (control: 724 ± 97, CON: 710 ± 77, ECC: 726 ± 72 mmol·L-1·120 min, p = .86) and insulin (control: 24995 ± 11229, CON: 23319 ± 10417, ECC: 21842 ± 10171 pmol·L-1·120 min, p = .48), peak glucose (control: 8.1 ± 1.3, CON: 7.7 ± 1.2, ECC: 7.7 ± 1.1 mmol·L-1, p = .63) and peak insulin levels (control: 361 ± 188, CON: 322 ± 179, ECC: 299 ± 152 pmol·L-1, p = .30) were similar. It was concluded that glucose tolerance and the insulin response to an OGTT were not changed immediately by muscle-damaging eccentric exercise.

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Ben B. Yaspelkis III and John L. lvy

The effect of a carbohydrate-arginine supplement on postexercise muscle glycogen storage was investigated. Twelve well-trained cyclists rode for 2 hr on two separate occasions to deplete theirmuscle glycogen stores. At 0, l, 2, and 3 hr after each exercise bout, the subjects ingested either a carbohydrate (CHO) supplement (1 g carbohydrate/kg body weight) or a carbohydrate-arginine (CHO/AA) supplement (1 g carbohydrate/kg body mass and 0.08 g arginine-hydrochloride/kg body weight). No difference in rate of glycogen storage was found between the CHO/AA and CHO treatments, although significance was approached. There were also no differences in plasma glucose, insulin, or blood lactate responses between treatments. Postexercise carbohydrate oxidation during the CHO/AA treatment was significantly reduced compared to the CHO treatment. These results suggest that the addition of arginine to a CHO supplement reduces the rate of CHO oxidation postexercise and therefore may increase the availability of glucose for muscle glycogen storage during recovery.

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Yan Burelle, François Péronnet, Denis Massicotte, Guy R. Brisson and Claude Hillaire-Marcel

The oxidation of 13C-labeled glucose and fructose ingested as a preexercise meal between 180 and 90 min before exercise was measured on 6 subjects when either a placebo or sucrose was ingested during the exercise period. Labeled hexose oxidation, which occurred mainly during the first hour of exercise, was not significantly modified when sucrose was ingested, but exogenous glucose oxidation was significantly higher than exogenous fructose oxidation in both situations. The results suggest that the absorption rate of exogenous hexoses was high when exercise was initiated but diminished thereafter, and that glucose and fructose released from sucrose ingested during exercise did not compete with glucose or fructose ingested before exercise for intestinal absorption, for conversion into glucose in the liver (for fructose), or for uptake and oxidation of glucose in peripheral tissues. However, as already shown, in terms of availability for oxidation of carbohydrates provided by the preexercise meal, glucose should be favored over fructose.

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Thomas D. Fahey, James D. Larsen, George A. Brooks, William Colvin, Steven Henderson and Darrel Lary

Five trained, fasted male cyclists rode a cycle ergometer three times at 50% of VO2,max for 180 min. Using a balanced order, double-blind procedure,subjects were given either a solution containing polylactate (PL: 80% polylactate, 20% sodium lactate, in 7% solution with water), glucose polymer (GP: multidextrin in 7% solution with water), or control (C: water sweetened with aspartame) 5 min before exercise and at 20-min intervals during exercise. Venous blood samples were taken at rest and at 20-min intervals during exercise. In general, PL and GP rendered similar results except that pH and bicarbonate (HCO3) were higher in PL. There were no differences between treatments in perceived exertion, sodium, potassium, chloride, lactate, heart rate, oxygen consumption, rectal temperature, or selected skin temperatures. These data show that polylactate may help maintain blood glucose and enhance blood buffering capacity during prolonged exercise and could be a useful component in an athletic fluid replacement beverage.