Fructose and glucose ingestion and muscle glycogen use during submaximal exercise

1983 ◽  
Vol 55 (6) ◽  
pp. 1767-1771 ◽  
Author(s):  
L. Levine ◽  
W. J. Evans ◽  
B. S. Cadarette ◽  
E. C. Fisher ◽  
B. A. Bullen
Keyword(s):  
Muscle Glycogen ◽  
Gastrocnemius Muscle ◽  
Respiratory Exchange Ratio ◽  
Venous Blood ◽  
Serum Glucose ◽  
Submaximal Exercise ◽  
Glycogen Depletion ◽  
O2 Uptake ◽  
Water Ingestion ◽  
Glucose Ingestion

Substrate utilization after fructose, glucose, or water ingestion was examined in four male and four female subjects during three treadmill runs at approximately 75% of maximal O2 uptake. Each test was preceded by three days of a carbohydrate-rich diet. The runs were 30 min long and were spaced at least 1 wk apart. Exercise began 45 min after ingestion of 300 ml of randomly assigned 75 g fructose (F), 75 g glucose (G), or control (C). Muscle glycogen depletion determined by pre- and postexercise biopsies (gastrocnemius muscle) was significantly (P less than 0.05) less during the F trial than during C or G. Venous blood samples revealed a significant increase in serum glucose (P less than 0.05) and insulin (P less than 0.01) within 45 min after the G drink, followed by a decrease (P less than 0.05) in serum glucose during the first 15 min of exercise, changes not observed in the C or F trials. Respiratory exchange ratio was higher (P less than 0.05) during the G than C or F trials for the first 5 min of exercise and lower (P less than 0.05) during the C trial compared with G or F for the last 15 min of exercise. These data suggest that fructose ingested before 30 min of submaximal exercise maintains stable blood glucose and insulin concentrations, which may lead to the observed sparing of muscle glycogen.

Muscle metabolism during exercise in the heat in unacclimatized and acclimatized humans

1985 ◽  
Vol 59 (5) ◽  
pp. 1350-1354 ◽  
Author(s):  
D. S. King ◽  
D. L. Costill ◽  
W. J. Fink ◽  
M. Hargreaves ◽  
R. A. Fielding
Keyword(s):  
Muscle Glycogen ◽  
Respiratory Exchange Ratio ◽  
Muscle Metabolism ◽  
Submaximal Exercise ◽  
Intense Exercise ◽  
O2 Uptake ◽  
Heat Acclimatization ◽  
Fuel Selection ◽  
Muscle Ph ◽  
Male Subjects

The effect of heat acclimatization on aerobic exercise tolerance in the heat and on subsequent sprint exercise performance was investigated. Before (UN) and after (ACC) 8 days of heat acclimatization, 10 male subjects performed a heat-exercise test (HET) consisting of 6 h of intermittent submaximal [50% of the maximal O2 uptake] exercise in the heat (39.7 degrees C dB, 31.0% relative humidity). A 45-s maximal cycle ride was performed before (sprint 1) and after (sprint 2) each HET. Mean muscle glycogen use during the HET was lower following acclimatization [ACC = 28.6 +/- 6.4 (SE) and UN = 57.4 +/- 5.1 mmol/kg; P less than 0.05]. No differences were noted between the UN and ACC trials with respect to blood glucose, lactate (LA), or respiratory exchange ratio. During the UN trial only, total work output during sprint 2 was reduced compared with sprint 1 (24.01 +/- 0.80 vs. 21.56 +/- 1.18 kJ; P less than 0.05). This reduction in sprint performance was associated with an attenuated fall in muscle pH following sprint 2 (6.86 vs. 6.67, P less than 0.05) and a reduced accumulation of LA in the blood. These data indicate that heat acclimatization produced a shift in fuel selection during submaximal exercise in the heat. The observed sparing of muscle glycogen may be associated with the enhanced ability to perform highly intense exercise following prolonged exertion in the heat.

Endurance training in older men and women II. Blood lactate response to submaximal exercise

1984 ◽  
Vol 57 (4) ◽  
pp. 1030-1033 ◽  
Author(s):  
D. R. Seals ◽  
B. F. Hurley ◽  
J. Schultz ◽  
J. M. Hagberg
Keyword(s):  
Endurance Training ◽  
Blood Lactate ◽  
Respiratory Exchange Ratio ◽  
Submaximal Exercise ◽  
Older Individuals ◽  
O2 Uptake ◽  
Men And Women ◽  
Low Intensity ◽  
Older Men And Women ◽  
Intensity Training

Seven men and four women (age 63 +/- 2 yr, mean +/- SD, range 61–67 yr) participated in a 12-mo endurance training program to determine the effects of low-intensity (LI) and high-intensity (HI) training on the blood lactate response to submaximal exercise in older individuals. Maximal oxygen uptake (VO2max), blood lactate, O2 uptake (VO2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (R) during three submaximal exercise bouts (65–90% VO2max) were determined before training, after 6 mo of LI training, and after an additional 6 mo of HI training. VO2max (ml X kg-1 X min-1) was increased 12% after LI training (P less than 0.05), while HI training induced a further increase of 18% (P less than 0.01). Lactate, HR, VE, and R were significantly lower (P less than 0.05) at the same absolute work rates after LI training, while HI training induced further but smaller reductions in these parameters (P greater than 0.05). In general, at the same relative work rates (ie., % of VO2max) after training, lactate was lower or unchanged, HR and R were unchanged, and VO2 and VE were higher. These findings indicate that LI training in older individuals results in adaptations in the response to submaximal exercise that are similar to those observed in younger populations and that additional higher intensity training results in further but less-marked changes.

Effect of hyperoxia on substrate utilization during intense submaximal exercise

1986 ◽  
Vol 61 (2) ◽  
pp. 523-529 ◽  
Author(s):  
R. P. Adams ◽  
P. A. Cashman ◽  
J. C. Young
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
Respiratory Exchange Ratio ◽  
Minute Ventilation ◽  
Exercise Bout ◽  
Substrate Utilization ◽  
Submaximal Exercise ◽  
O2 Uptake ◽  
Co2 Output ◽  
Lactate Levels

Six trained males [mean maximal O2 uptake (VO2max) = 66 ml X kg-1 X min-1] performed 30 min of cycling (mean = 76.8% VO2max) during normoxia (21.35 +/- 0.16% O2) and hyperoxia (61.34 +/- 1.0% O2). Values for VO2, CO2 output (VCO2), minute ventilation (VE), respiratory exchange ratio (RER), venous lactate, glycerol, free fatty acids, glucose, and alanine were obtained before, during, and after the exercise bout to investigate the possibility that a substrate shift is responsible for the previously observed enhanced performance and decreased RER during exercise with hyperoxia. VO2, free fatty acids, glucose, and alanine values were not significantly different in hyperoxia compared with normoxia. VCO2, RER, VE, and glycerol and lactate levels were all lower during hyperoxia. These results are interpreted to support the possibility of a substrate shift during hyperoxia.

Aldosterone and prolactin response to exercise in the heat in circumpubertal boys

1991 ◽  
Vol 71 (5) ◽  
pp. 1741-1745 ◽  
Author(s):  
B. Falk ◽  
O. Bar-Or ◽  
J. D. MacDougall
Keyword(s):  
Venous Blood ◽  
Plasma Osmolality ◽  
O2 Uptake ◽  
Hormonal Responses ◽  
Tanner Staging ◽  
Water Ingestion ◽  
Physical Maturation ◽  
Prolactin Response ◽  
Response To Exercise ◽  
Percent Decrease

Thermoregulatory responses to exercise in the heat, especially sweating pattern, differ between children and adults. To determine whether such differences may be related to hormonal responses and to assess the possible association between this response and physical maturation, three groups of circumpubertal boys cycled at 50% of maximal O2 uptake (three 20-min bouts with 10 min of rest between bouts) in 42 degrees C at 20% relative humidity. On the basis of Tanner staging, 11 were prepubertal (PP), 12 midpubertal (MP), and 7 late pubertal (LP). Water ingestion was encouraged to minimize dehydration. Venous blood was sampled before and immediately after the session. Changes in heart rate, rectal temperature, and percent decrease in plasma volume did not differ among groups. There was no change in plasma osmolality in any of the groups. Resting testosterone concentrations were higher with increased level of physical maturity (PP = 0.4 +/- 0.1, MP = 8.2 +/- 1.9, LP = 13.8 +/- 1.2 nmol/l; P less than 0.05). In all groups, both aldosterone (ALD) and prolactin (PRL) markedly increased after exercise in the heat (ALD: PP = 161 +/- 40 vs. 1,289 +/- 263, MP = 173 +/- 47 vs. 1,245 +/- 153, LP = 250 +/- 76 vs. 1,681 +/- 400 pmol/l; PRL: PP = 8.1 +/- 1.2 vs. 24.9 +/- 4.2, MP = 8.8 +/- 1.0 vs. 22.0 +/- 8.9, LP = 8.4 +/- 0.8 vs. 39.0 +/- 3.6 micrograms/l; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose ingestion before and during intense exercise

1981 ◽  
Vol 50 (4) ◽  
pp. 766-771 ◽  
Author(s):  
A. Bonen ◽  
S. A. Malcolm ◽  
R. D. Kilgour ◽  
K. P. MacIntyre ◽  
A. N. Belcastro
Keyword(s):  
Blood Glucose ◽  
Muscle Glycogen ◽  
Respiratory Exchange Ratio ◽  
Intense Exercise ◽  
Pilot Studies ◽  
Persistent Effect ◽  
Considerable Portion ◽  
Glucose Ingestion ◽  
Insulin Responses ◽  
Glucose Group

Glucose and insulin responses were compared in glycogen depleted subjects when glucose (1.5 g/kg) was ingested 15 min before (n = 7) or during (min 3-5) intense exercise (80% VO2 max; n = 8). A nonexercise group (n = 8) and a no-glucose group (n = 8) were also included for comparisons. A 36- to 44-h fast, combined with exhaustive exercise to deplete muscle glycogen, (congruent to 80% in pilot studies) suggested that the subjects initiated exercise with substantially depleted hepatic and muscle glycogen reserves. With no glucose ingestion, blood glucose decreased during exercise (P less than 0.05) and blood lactate (HLa congruent to 3.8 mM) and the respiratory exchange ratio (R) remained low (0.83); with glucose ingestion before or during exercise, HLa concentrations were doubled (7.3 mM) and R was greater (0.90-0.92; P less than 0.05). Although insulin concentrations decreased rapidly to basal levels within 10 min after the onset of exercise in the preexercise glucose group (P less than 0.05), blood glucose continued to decrease throughout exercise. No such decrease occurred in the subjects who ingested glucose during exercise, nor did insulin concentrations change markedly in this group (P greater than 0.05). The HLa and R data indicated that a considerable portion of glucose was metabolized during exercise. Differences in the preexercise insulin environment appear to exert a persistent effect on glucose uptake throughout exercise.

Adenosine infusion does not improve maximal O2 uptake in isolated working dog muscle

1994 ◽  
Vol 76 (6) ◽  
pp. 2820-2824 ◽  
Author(s):  
S. S. Kurdak ◽  
M. C. Hogan ◽  
P. D. Wagner
Keyword(s):  
Vascular Resistance ◽  
Gastrocnemius Muscle ◽  
Venous Blood ◽  
Blood Gases ◽  
O2 Uptake ◽  
Vascular Perfusion ◽  
Fick Principle ◽  
O2 Extraction ◽  
Before And After ◽  
O2 Delivery

We asked whether maximally working muscle could increase O2 extraction at fixed O2 delivery [i.e., improve maximal O2 uptake (VO2max)] when vascular resistance was decreased with adenosine (A) infusion. We postulated that a reduction in vascular resistance at the same blood flow (Q) might result in more uniform vascular perfusion and also possibly increase red blood cell transit time, thereby potentially improving the ability of the tissue to extract O2. Pump-perfused isolated dog gastrocnemius muscle (n = 6) was stimulated maximally at each of two levels of Q: 110 +/- 3 and 54 +/- 4 (SE) ml.100 g-1.min-1 [normal control (C) and ischemia (I), respectively], both before and after giving 10(-2) M of A solution in each case. Arterial and venous blood samples were taken to measure blood gases, and the Fick principle was used to calculate O2 uptake. Resistance decreased significantly after A treatment in both groups (1.2 +/- 0.1 vs. 0.9 +/- 0.1 and 1.3 +/- 0.1 vs. 1.1 +/- 0.1 mmHg.ml-1.100 g.min for C vs. C + A and I vs. I + A, respectively; P < 0.01). O2 delivery was lower with I but did not change at either perfusion rate when A was infused. VO2max also decreased significantly with I but was no different when A was added (13.8 +/- 0.7 vs. 13.8 +/- 0.9 and 8.4 +/- 0.5 vs. 8.2 +/- 0.6 ml.100 g-1.min-1 for C vs. C + A and I vs. I + A, respectively). These results show that the decrease in resistance with A did not lead to changes in VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of glycogen in control of glycolysis and IMP formation in human muscle during exercise

1991 ◽  
Vol 260 (6) ◽  
pp. E859-E864 ◽  
Author(s):  
M. K. Spencer ◽  
A. Katz
Keyword(s):  
Muscle Glycogen ◽  
Work Load ◽  
Amp Deaminase ◽  
Glycogen Depletion ◽  
Intense Exercise ◽  
O2 Uptake ◽  
Contraction Phase ◽  
Muscle Ph ◽  
Glycogen Stores

The effect of prior glycogen depletion on glycolysis [flux through phosphofructokinase (PFK)] and inosine monophosphate (IMP) formation in human skeletal muscle has been investigated. Eight subjects cycled at a work load calculated to elicit 95% of maximal O2 uptake on two occasions, the first to fatigue [5.5 +/- 0.3 (SE) min] and the second at the same workload and for the same duration as the first. Before the first experiment, muscle glycogen stores were lowered by a combination of exercise and diet. Before the second experiment, muscle glycogen stores were supercompensated. In the low-glycogen (LG) state muscle glycogen decreased from 201 +/- 31 mmol glucosyl units/kg dry wt at rest to 105 +/- 28 after exercise, and in the high-glycogen (HG) state from 583 +/- 40 to 460 +/- 49. The accumulation of fructose 6-phosphate (F-6-P; activator of PFK) during exercise was markedly attenuated in the LG state (P less than 0.01), whereas lactate accumulation in muscle was similar between treatments, suggesting that muscle pH was also similar. Glycolysis (estimated from glycogenolysis minus accumulation of hexose monophosphates) was not measurably different between treatments (LG = 88 +/- 17, HG = 106 +/- 43 mmol/kg dry wt; P greater than 0.05). IMP was significantly greater in the LG state after exercise (3.63 +/- 0.85 vs. 1.97 +/- 0.44 mmol/kg dry wt; P less than 0.05). It is concluded that decreased glycogen availability does not measurably alter the rate of muscle glycolysis during intense exercise. It is hypothesized that the attenuated increase in F-6-P in the LG state, which should theoretically decrease glycolysis, is compensated for by increases in free ADP and AMP (activators of PFK) at the enzymatic site during the contraction phase. The greater increase in IMP in the LG state is consistent with this hypothesis, since ADP and AMP are also activators of AMP deaminase.

scholarly journals Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists

2015 ◽  
Vol 309 (12) ◽  
pp. E1032-E1039 ◽  
Author(s):  
Javier T. Gonzalez ◽  
Cas J. Fuchs ◽  
Fiona E. Smith ◽  
Pete E. Thelwall ◽  
Roy Taylor ◽  
...  
Keyword(s):  
Muscle Glycogen ◽  
Liver Glycogen ◽  
Whole Body ◽  
Peak Power Output ◽  
Resonance Spectroscopy ◽  
Glycogen Depletion ◽  
Carbohydrate Utilization ◽  
Glucose Ingestion ◽  
Before And After ◽  
Effect Of Glucose

The purpose of this study was to define the effect of glucose ingestion compared with sucrose ingestion on liver and muscle glycogen depletion during prolonged endurance-type exercise. Fourteen cyclists completed two 3-h bouts of cycling at 50% of peak power output while ingesting either glucose or sucrose at a rate of 1.7 g/min (102 g/h). Four cyclists performed an additional third test for reference in which only water was consumed. We employed 13C magnetic resonance spectroscopy to determine liver and muscle glycogen concentrations before and after exercise. Expired breath was sampled during exercise to estimate whole body substrate use. After glucose and sucrose ingestion, liver glycogen levels did not show a significant decline after exercise (from 325 ± 168 to 345 ± 205 and 321 ± 177 to 348 ± 170 mmol/l, respectively; P > 0.05), with no differences between treatments. Muscle glycogen concentrations declined (from 101 ± 49 to 60 ± 34 and 114 ± 48 to 67 ± 34 mmol/l, respectively; P < 0.05), with no differences between treatments. Whole body carbohydrate utilization was greater with sucrose (2.03 ± 0.43 g/min) vs. glucose (1.66 ± 0.36 g/min; P < 0.05) ingestion. Both liver (from 454 ± 33 to 283 ± 82 mmol/l; P < 0.05) and muscle (from 111 ± 46 to 67 ± 31 mmol/l; P < 0.01) glycogen concentrations declined during exercise when only water was ingested. Both glucose and sucrose ingestion prevent liver glycogen depletion during prolonged endurance-type exercise. Sucrose ingestion does not preserve liver glycogen concentrations more than glucose ingestion. However, sucrose ingestion does increase whole body carbohydrate utilization compared with glucose ingestion. This trial was registered at https://www.clinicaltrials.gov as NCT02110836.

Muscle metabolism during exercise and heat stress in trained men: effect of acclimation

1994 ◽  
Vol 76 (2) ◽  
pp. 589-597 ◽  
Author(s):  
M. A. Febbraio ◽  
R. J. Snow ◽  
M. Hargreaves ◽  
C. G. Stathis ◽  
I. K. Martin ◽  
...  
Keyword(s):  
Heart Rate ◽  
Relative Humidity ◽  
Respiratory Exchange Ratio ◽  
Muscle Metabolism ◽  
Type I ◽  
Plasma Epinephrine ◽  
Glycogen Depletion ◽  
O2 Uptake ◽  
Type I Fibers ◽  
Fuel Source

Exercise metabolism was examined in 13 endurance athletes who exercised on three occasions for 40 min at 70% of maximal O2 uptake in an environmental chamber at either 20 degrees C and 20% relative humidity (RTT) or 40 degrees C and 20% relative humidity before (PRE ACC) or after (POST ACC) 7 days of acclimation. Exercise in the heat resulted in a lower (P < 0.05) mean O2 uptake (0.13 l/min) and higher (P < 0.01) heart rate and respiratory exchange ratio. Acclimation resulted in a lower (P < 0.01) mean heart rate and respiratory exchange ratio. Postexercise rectal temperature, muscle temperature, muscle and blood lactate, and blood glucose were higher (P < 0.01) in the PRE ACC than in the RTT trial, but all were reduced (P < 0.01) in the POST ACC compared with the PRE ACC trial. Muscle glycogenolysis and percentage of type I muscle fibers showing glycogen depletion were greater (P < 0.05) in the PRE ACC than in the RTT trial. Muscle glycogenolysis was unaffected by acclimation during exercise in the heat, although the percentage of depleted type I fibers was higher (P < 0.05) in the unacclimated state. Plasma epinephrine was higher (P < 0.01) during exercise in the heat in the unacclimated individual relative to RTT but was lower (P < 0.01) in the POST ACC than in the PRE ACC trial. The greater reliance on carbohydrate as a fuel source during exercise in the heat appears to be partially reduced after acclimation. These alterations are consistent with the observed changes in plasma epinephrine concentrations.

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