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Costas A. Anastasiou, Stavros A. Kavouras, Christina Koutsari, Charalambos Georgakakis, Katerina Skenderi, Michael Beer and Labros S. Sidossis

This study examined the effect of maltose-containing sports drinks on exercise performance. Ten subjects completed 4 trials. Each trial consisted of a glycogen depletion protocol, followed by a 15-min refueling, after which subjects performed an 1-h performance test while consuming one of the experimental drinks (HGlu, glucose; HMal, maltose; MalMix, sucrose, maltose, and maltodextrin; Plac, placebo). Drinks provided 0.65 g/kg body weight carbohydrates during refueling and 0.2 g/kg every 15 min during the performance test. Although no significant differences were found in performance (HGlu: 67.2 ± 2.0; HMal: 68.6 ± 1.7; MalMix: 66.7 ± 2.0; Plac: 69.4 ± 3.0 min, P > 0.05), subjects completed the MalMix trial 3.9% faster than the Plac. Carbohydrate drinks caused comparable plasma glucose values that were significantly higher during refueling and at the end of exercise, compared to Plac. The data suggest that although carbohydrate drinks help to maintain plasma glucose at a higher level, no differences in performance could be detected after glycogen-depleting exercise.

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Nicholas M. Edwards, Heidi J. Kalkwarf, Jessica G. Woo, Philip R. Khoury, Stephen R. Daniels and Elaine M. Urbina

Purpose:

The objective of this study was to characterize the relationship between objectively-measured physical activity (PA) and cardiovascular risk factors in 7-year-old children and test the hypothesis that it differs by race.

Methods:

Cross-sectional study of 308 7-year-old children drawn from a major US metropolitan community. PA (moderate-to-vigorous, MVPA; light, LPA; and inactivity, IA) was measured by accelerometry (RT3). Cardiovascular risk factors included BMI, blood pressure, and serum lipids, glucose and insulin concentrations. General linear modeling was used to evaluate the independent associations between PA measures and cardiovascular risk factors and interactions by race.

Results:

In black children, greater time spent in PA was independently associated with lower levels of triglycerides (MVPA and LPA, both p < .01), glucose (MVPA, p < .05), and insulin (MVPA, p < .01); these associations were not evident in white children. Across races, greater inactivity was independently associated with greater low-density lipoprotein cholesterol in overweight participants (p < .01) but not in normal weight participants. No PA measure was associated with BMI, systolic blood pressure, or high-density lipoprotein cholesterol.

Conclusions:

In this cohort of 7-year-old children, the relationship between PA and some cardiovascular risk factors differed by race. These findings may have implications for targeting of PA promotion efforts in children.

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Elin Ekblom-Bak, Örjan Ekblom, Kate A. Bolam, Björn Ekblom, Göran Bergström and Mats Börjesson

Background:

Although moderate-to-vigorous physical activity (MVPA) is mainly recommended for glucose control, light physical activity (LIPA) may also have the potential to induce favorable changes. We investigated sedentary time (SED) substitution with equal time in LIPA and MVPA, and the association with markers of glucose regulation and insulin sensitivity after stratification by waist circumference, fitness and fasting glucose levels.

Methods:

A total of 654 men and women, 50 to 64 years, from the SCAPIS pilot study were included. Daily SED, LIPA and MVPA were assessed using hip-worn accelerometers. Fasting plasma glucose, insulin and HOMA-IR were determined.

Results:

Substituting 30 min of SED with LIPA was significantly associated with 3.0% lower fasting insulin values and 3.1% lower HOMA-IR values, with even lower levels when substituting SED with MVPA. Participants with lower fitness and participants with high fasting glucose levels benefited significantly more from substituting 30 min of SED with LIPA compared with participants with normal to high fitness levels and participants with normal glucose levels, respectively.

Conclusions:

LIPA, and not only MVPA, may have beneficial associations with glucose regulation. This is of great clinical and public health importance, not least because it may confer a higher compliance rate to regular PA.

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Manuel Lugo, William M. Sherman, Gregory S. Wimer and Keith Garleb

This study examined the effects of consuming the same amount of carbohydrate in solid form, liquid form, or both on metabolic responses during 2 hrs of cycling at 70% peak VO2 and on cycling time-trial performance. Subjects consumed 0.4 g carbohydrate/kg body mass before and every 30 min during exercise. The liquid was a 7% carbohydrate-electrolyte beverage and the solid was a sports bar (1171 kJ) in which 76%, 18%, and 6% of total energy was derived from carbohydrate, fat, and protein, respectively. Blood obtained at baseline, before exercise, and every 30 min was analyzed for glucose, insulin, lactate, hemoglobin, hematocrit, and plasma volume. There were no differences among the treatments for the blood parameters. Total carbohydrate oxidation and time-trial performance were also similar among treatments. Under thermoneutral conditions with equal liquid inges-tion, the metabolic and performance responses are similar when consuming carbohydrate as a liquid, solid, or in combination during prolonged, moderate intensity cycling.

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Petra Stiegler, S. Andrew Sparks and Adam Cunliffe

Maximizing postprandial energy expenditure and fat oxidation could be of clinical relevance for the treatment of obesity. This study investigated the effect of prior exercise on energy expenditure and substrate utilization after meals containing varying amounts of macronutrients. Eight lean (11.6% ± 4.0% body fat, M ± SD) and 12 obese (35.9% ± 5.3% body fat) men were randomly assigned to a protein (43% protein, 30% carbohydrate) or a carbohydrate (10% protein, 63% carbohydrate) meal. The metabolic responses to the meals were investigated during 2 trials, when meals were ingested after a resting period (D) or cycling exercise (Ex+D; 65% of oxygen consumption reserve, 200 kcal). Energy expenditure, substrate utilization, and glucose and insulin responses were measured for 4 hr during the postprandial phase. Although postprandial energy expenditure was not affected by prior exercise, the total amount of fat oxidized was higher during Ex+D than during D (170.8 ± 60.1 g vs. 137.8 ± 50.8 g, p < .05), and, accordingly, the use of carbohydrate as substrate was decreased (136.4 ± 45.2 g vs. 164.0 ± 42.9 g, p < .05). After the protein meal fat-oxidation rates were higher than after carbohydrate intake (p < .05), an effect independent of prior exercise. Plasma insulin tended to be lower during Ex+D (p = .072) and after the protein meal (p = .066). No statistically significant change in postprandial blood glucose was induced by prior exercise. Exercising before meal consumption can result in a marked increase in fat oxidation, which is independent of the type of meal consumed.

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Michael C. Riddell, Sara L. Partington, Nicole Stupka, David Armstrong, C. Rennie and Mark A. Tarnopolsky

Compared to males, females oxidize proportionately more fat and less carbohydrate during endurance exercise performed in the fasted state. This study was designed to test the hypothesis that there may also be gender differences in exogenous carbohydrate (CHOexo) oxidation during exercise. Healthy, young males (n = 7) and females (n = 7) each completed 2 exercise trials (90 min cycle ergometry at 60% VO2peak), 1 week apart. Females were eumenorrheic and were tested in the midfollicular phase of their menstrual cycle. Subjects drank intermittently either 8% CHOexo (1 g glucose · kg · h−1) enriched with U-13C glucose or an artificially sweetened placebo during the trial. Whole-body substrate oxidation was determined from RER, urinary urea excretion, and the ratio of 13C:12C in expired gas during the final 60 min of exercise. During the placebo trial, fat oxidation was higher in females than in males (0.42 · 0.07 vs. 0.32 · 0.09 g · min−1 · kg LBM–1 × 10–2) at 30 min of exercise (p < .05). When averaged over the final 60 min of exercise, the relative proportions of fat, total carbohydrate, and protein were similar between groups. During CHOexo ingestion, both the ratio of 13C:12C in expired gas (p < .05) and the proportion of energy derived from CHOexo relative to LBM (p < .05) were higher in females compared to males at 75- and 90-min exercise. When averaged over the final 60 min of exercise, the percentage of CHOexo to the total energy contribution tended to be higher in females (14.3 · 1.2%) than in males (11.2 · 1.2%; p = .09). The reduction in endogenous CHO oxidation with CHOexo intake was also greater in females (12.9 · 3.1%) than in males (5.1 · 2.0%; p = .05). Compared to males, females may oxidize a greater relative proportion of CHOexo during endurance exercise which, in turn, may spare more endogenous fuel. Based on these observations, ingested carbohydrate may be a particularly beneficial source of fuel during endurance exercise for females.

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Ann M. Swartz, Scott J. Strath, Sarah J. Parker and Nora E. Miller

The purpose of this study was to investigate the combined impact of obesity and physical activity (PA) on the health of older adults. Pedometer-determined steps/d, body-mass index (BMI), resting blood pressure, and fasting glucose (FG) were assessed in 137 older adults (69.0 ± 8.9 yr). The active group (>4,227 steps/d) had lower systolic blood pressure (SBP; p = .001), diastolic blood pressure (DBP; p = .028), and FG (p < .001) than the inactive group (≤4,227 steps/d). The normal-BMI group (18.5-24.9 kg/m2) had lower SBP (p < .001) and DBP (p = .01) than the obese group (≤30 kg/m2). There were no differences in SBP (p = .963) or DBP (p = 1.0) between active obese and inactive normal-BMI groups. The active obese group, however, had a more favorable FG than the inactive normal-BMI group (χ2 = 18.9, df = 3, p = .001). Efforts to increase PA of older adults should receive the same priority as reducing obesity to improve BP and FG levels.

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Marcos Echegaray, Lawrence E. Armstrong, Carl M. Maresh, Deborah Riebe, Robert W. Kenefick, John W. Castellani, Stavros Kavouras and Douglas Casa

This study assessed the plasma glucose (PG) and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. On separate days, 8 subjects (21.0 ± 1.8 years; 57.3 ± 3.7 ml · kg−1 · min−1) exercised at 50% V̇O2maxin a 33 °C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml · kg−1) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g · kg−1 of carbohydrate and underwent an exercise test (treadmill walking, 50% V̇O2max, 36 °C) for up to 90 min. Compared to pre-exercise level (294 mg · dl−1), PG increased significantly (>124 mg · dl−1) at 15 min of the exercise test in all trials and remained significantly elevated for 75 min in NF, 30 min more than in the 2 rehydration trials. Although serum Insulin increased significantly at 15 min of exercise in the 45IV trial (7.2 ± 1.2 vs. 23.7 ± 4.7 μIU · ml−1) no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 ± 66 pg · ml−1) compared to the 45IV and 9IV trials (472 ± 55 and 474 ± 52 pg · ml−1, respectively). In conclusion, ingestion of a small solid carbohydrate load prior to exercise in the 4% hypohydration level resulted in prolonged high PG concentration compared to partial IV rehydration.

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Jens Bangsbo, Fedon Marcello Iaia and Peter Krustrup

The physical demands in soccer have been studied intensively, and the aim of the present review is to provide an overview of metabolic changes during a game and their relation to the development of fatigue. Heart-rate and body-temperature measurements suggest that for elite soccer players the average oxygen uptake during a match is around 70% of maximum oxygen uptake (VO2 max). A top-class player has 150 to 250 brief intense actions during a game, indicating that the rates of creatine-phosphate (CP) utilization and glycolysis are frequently high during a game, which is supported by findings of reduced muscle CP levels and several-fold increases in blood and muscle lactate concentrations. Likewise, muscle pH is lowered and muscle inosine monophosphate (IMP) elevated during a soccer game. Fatigue appears to occur temporarily during a game, but it is not likely to be caused by elevated muscle lactate, lowered muscle pH, or change in muscle-energy status. It is unclear what causes the transient reduced ability of players to perform maximally. Muscle glycogen is reduced by 40% to 90% during a game and is probably the most important substrate for energy production, and fatigue toward the end of a game might be related to depletion of glycogen in some muscle fibers. Blood glucose and catecholamines are elevated and insulin lowered during a game. The blood free-fatty-acid levels increase progressively during a game, probably reflecting an increasing fat oxidation compensating for the lowering of muscle glycogen. Thus, elite soccer players have high aerobic requirements throughout a game and extensive anaerobic demands during periods of a match leading to major metabolic changes, which might contribute to the observed development of fatigue during and toward the end of a game.

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Laura A. Brocklebank, Rob C. Andrews, Angie Page, Catherine L. Falconer, Sam Leary and Ashley Cooper

Background:

The aim of this randomized, 3-period, 3-treatment crossover trial was to examine the acute effects of regularly breaking up seated office work with short bouts of standing or light-intensity walking on postprandial interstitial glucose concentration.

Methods:

Seventeen middle-aged office workers performed 3 5-hour trial conditions at their workplace in a random order: 1) uninterrupted sitting, 2) sitting interrupted by 2 minutes of standing every 20 minutes, and 3) sitting interrupted by 2 minutes of light-intensity walking every 20 minutes. Participants consumed 2 standardized test drinks at the start of each trial condition and an iPro2 continuous glucose monitoring system (CGMS) recorded average interstitial glucose concentration every 5 minutes for the duration of the study.

Results:

The 5-hour interstitial glucose incremental area under the curve (iAUC) was 55.5% lower after sitting interrupted by light-intensity walking compared with after uninterrupted sitting (95% CI, –104.2% to –6.8%). There was also a suggestion of a beneficial effect of regular standing breaks, particularly in overweight men, although they were not as effective as the walking breaks (mean difference [95% CI], –29.6% [–73.9% to 14.7%]).

Conclusions:

Regularly breaking up prolonged sitting lowers postprandial glycemia in middle-aged adults without metabolic impairment.