Biomedical subjects

W J Fink

Publications and source records attributed to W J Fink.

At least 55 records · Page 3Linked to original sources

PubMed1989

Threshold for muscle lactate accumulation during progressive exercise.

The purpose of this study was to investigate the relationship between muscle and blood lactate concentrations during progressive exercise. Seven endurance-trained male college students performed three incremental bicycle ergometer exercise tests. The first two tests (tests I and II) were identical and consisted of 3-min stage durations with 2-min rest intervals and increased by 50-W increments until exhaustion. During these tests, blood was sampled from a hyperemized earlobe for lactate and pH measurement (and from an antecubital vein during test I), and the exercise intensities corresponding to the lactate threshold (LT), individual anaerobic threshold (IAT), and onset of blood lactate accumulation (OBLA) were determined. The test III was performed at predetermined work loads (50 W below OBLA, at OBLA, and 50 W above OBLA), with the same stage and rest interval durations of tests I and II. Muscle biopsies for lactate and pH determination were taken at rest and immediately after the completion of the three exercise intensities. Blood samples were drawn simultaneously with each biopsy. Muscle lactate concentrations increased abruptly at exercise intensities greater than the "below-OBLA" stage [50.5% maximal O2 uptake (VO2 max)] and resembled a threshold. An increase in blood lactate and [H+] also occurred at the below-OBLA stage; however, no significant change in muscle [H+] was observed. Muscle lactate concentrations were highly correlated to blood lactate (r = 0.91), and muscle-to-blood lactate ratios at below-OBLA, at-OBLA, and above-OBLA stages were 0.74, 0.63, 0.96, and 0.95, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Influence of carbohydrate dosage on exercise performance and glycogen metabolism.

This study was undertaken to examine the effects of ingestion of carbohydrate (CHO) solutions of 0 (WP), 6 (CHO-6), 12 (CHO-12), and 18 g CHO/100 ml (CHO-18) on performance and muscle glycogen use. Ten trained cyclists performed five 120-min cycling trials. The first 105 min of each trial was at 70% of maximal O2 consumption (VO2max), and the final 15 min was an all-out performance ride on an isokinetic cycle ergometer equipped to measure total work output. In one of the trials (CHO-12I) the submaximal portion of the ride consisted of seven 15-min rides at 70% of VO2max with a 3-min rest between each ride. Every 15 min the men consumed 8.5 ml.kg-1.h-1 (approximately 150 ml) of one of the four test solutions. Venous blood samples were obtained every 15 min for glucose and insulin. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen and sectioned and stained for myosin adenosinetriphosphatase and glycogen for single fiber depletion measurements. There were no differences in glycogen use (86.7 +/- 6.0, 75.5 +/- 7.9, and 83.5 +/- 5.5 mmol/kg for the WP, CHO-12C, and CHO-12I, respectively) or depletion patterns between the WP and the two CHO-12 trials. Blood glucose was significantly elevated in both the CHO-12 trials and in the CHO-18 trial compared with the WP trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Gastric emptying: influence of prolonged exercise and carbohydrate concentration.

Gastric emptying: influence of prolonged exercise and carbohydrate concentration, Med. Sci. Sports Exerc., Vol. 21, No. 3, pp. 269-274, 1989. The purpose of this study was to examine the effects of serial feedings of different concentrations of carbohydrate (CHO) on gastric emptying and to compare the rates of gastric emptying at rest and during prolonged exercise. Solutions of 0, 6, 12, and 18 g. 100 ml-1 (WP, CHO-6, CHO-12, and CHO-18, respectively) were tested. Ten trained male cyclists performed five trials involving 120 min of cycling. The first 105 min were at 70% of VO2max, and the final 15 min were an all-out self-paced performance ride. In one of the five trials, the subjects rode intermittently, completing seven 15-min rides at 70% of VO2max, with 3 min of rest between each ride. Every 15 min, approximately 150 ml (8.5 ml.kg-1.h-1) of one of the four test solutions were consumed. (In the intermittent trial, the CHO-12 solution was used.) Subjects were also tested during 120 min of seated rest using the above feeding schedule (6% solution). Gastric residue was determined by stomach aspiration following the performance ride. The volumes emptied during the CHO-12 and CHO-18 trials (1,049.8 and 889.2 ml) were significantly different from each other and were less than during the WP and CHO-6 trials (1,210.3 and 1,185.6 ml) (P less than 0.05). CHO delivery was significantly higher in the CHO-12 and CHO-18 trials (126 and 160 g) compared to the CHO-6 trial (71.1 g).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Human vitamin B-6 pools estimated through muscle biopsies.

Previous estimates of total vitamin B-6 pools in humans based on extrapolations from tracer studies yielded values of 107-190 mumol when the tracer was administered orally and 345-725 mumol when the tracer was administered intravenously. To obtain a more direct estimate of vitamin B-6 pools, muscle biopsies from five female and seven male adults were analyzed by cation-exchange chromatography. Total muscle mass was estimated from creatinine excretion and the assumption that muscle is 40% of the body weight. The total muscle vitamin B-6 pool was estimated to be 917 +/- 319 mumol in the females and 850 +/- 216 mumol in the males. Because muscle accounts for approximately 80% of the vitamin B-6 in the body, the total body pool of vitamin B-6 in adult humans is probably approximately 1000 mumol.

Adult↗

PubMed1988

Impaired muscle glycogen storage after muscle biopsy.

To assess the effects of repeated needle biopsies on the rate of muscle glycogen repletion, eight male subjects were studied immediately after and 2 days after an exhaustive cycling bout. A single biopsy was obtained from the right vastus lateralis muscle immediately after an exhaustive cycling bout. Two days later, a sample was taken 1 cm lateral or medial to sample A. In four of these subjects, additional biopsies were taken 3 cm distal and proximal. A control specimen was also taken from the left leg 2 days after the exercise. Ten days after the exercise, muscle was again sampled from each leg of these four subjects. Analysis of these samples revealed that the initial biopsy impaired glycogen storage in the muscle taken 1 cm medial or lateral to the previous site. This reduction in glycogen storage was most pronounced in the first 2 days after the exercise. Samples taken distal and proximal to the initial biopsy contained, on the average, less glycogen than the contralateral leg, but these differences were only significantly different in the distal muscle sample. Alteration in muscle glycogen storage was seen to persist for 10 days after the first biopsy, suggesting that care must be taken in selecting the site for repeated biopsies from the same muscle.

Adult↗

PubMed1988

Carbohydrate balance in competitive runners during successive days of intense training.

This study was designed to investigate the effect of intense training on muscle glycogen stores under conditions of controlled carbohydrate (CHO) intake. On two separate occasions, 10 highly trained distance runners increased their training load for 5 days (20 km/day, approximately 80% maximal O2 consumption) while eating a diet whose carbohydrate composition either equaled (EQ-CHO) or contained approximately 50% of the runner's estimated daily expenditure (LO-CHO). Total muscle glycogen levels were lower after the LO-CHO regimen. Photometric analysis of the glycogen content in individual fibers revealed that 27% type I and 17% type II fibers had optical densities less than 0.2 U after the LO-CHO regimen, whereas 7% type I and 0% type II were similarly depleted after the EQ-CHO diet. A linear relationship was observed between the histochemical and direct chemical analysis of muscle glycogen content. Treadmill O2 uptake measured at 185 and 238 m/min was higher during the LO-CHO than the EQ-CHO regimen. Ratings of perceived exertion were higher during the 238-m/min run for the LO-CHO regimen. After 3 days of rest, running economy and perception of effort returned to pretraining levels and muscle glycogen stores were approximately 85% of the pretraining values. Thus when CHO intake was only approximately 50% of the energy requirements there was a marked depletion of muscle glycogen stores, particularly in type I fibers, and a concomitant decrease in running economy and increased perception of fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Physiological responses to successive days of intense training in competitive swimmers.

To examine the physiological responses to successive days of intense training, 12 male collegiate swimmers doubled their training distance (4,266 +/- 264 to 8,970 +/- 161 m.d-1) while maintaining the intensity at approximately 95% VO2max for 10 d. Blood samples were obtained pre-exercise and immediately and 5 min after a sub-maximal (approximately 95% VO2max) front crawl swim (365.8 m) on days 0, 5, and 11. Swim performance was assessed from a maximal front crawl swim (365.8 m), two maximal front crawl sprints (22.9 m), and a semi-tethered swim power test. No significant changes were observed in performance. Pre-exercise serum cortisol (17.5 +/- 1.5, 19.5 +/- 1.6, and 20.6 +/- 1.2 micrograms.dl-1 for days 0, 5, and 11, respectively) and creatine kinase (56.2 +/- 7.7, 93.1 +/- 10.1, and 119.0 +/- 23.1 U.l-1 for days 0, 5, and 11, respectively) values were significantly elevated (P less than 0.05) on days 5 and 11 compared to day 0. Resting plasma catecholamine concentrations were higher but not significantly different (P greater than 0.05) at the end of the training period. Measurements of hemoglobin and hematocrit indicated a relative increase of 11.4 +/- 2.7% (P less than 0.05) in estimated plasma volume during the training period. Resting blood glucose values were unaffected by the training regimen while small but significant decreases in resting blood lactate values (1.01 +/- 0.06, 0.85 +/- 0.06, and 0.86 +/- 0.06 mmol.l-1 for days 0, 5, and 11, respectively) were observed on days 5 and 11. Resting heart rate and systolic blood pressure were not affected by the increased training load.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗

PubMed1988

Effects of carbohydrate ingestion on gastric emptying and exercise performance.

In an effort to determine the effects of 5 (CHO-5), 6 (CHO-6), and 7.5 (CHO-7.5) percent carbohydrate solutions on gastric emptying and performance, 8 trained male cyclists performed 4 trials of intermittent (7- x ;12-min bout) cycling at 70% VO2max. A final 12-min self-paced "performance" ride was performed on an isokinetic ergometer (Fitron) interfaced with a computer to provide total work output. A water placebo (WP) was used as a control. Each 12-min ride was followed by 3-min rest, during which a drink was consumed (8.5 ml.kg-1; mean total = 1,336 ml.2 h-1). Blood samples were taken at 0, 25, 55, 85, and 115 min for blood glucose analysis. Following the performance ride, gastric residue was obtained by intubation and aspiration. Of the original 1,336 ml ingested during each trial, the volumes emptied by the stomach for the four trials were 1,306 +/- 76, 1,262 +/- 82, 1,288 +/- 75, and 1,278 +/- 77 ml (+/- SE) for WP, CHO-5, CHO-6, and CHO-7.5, respectively. Only the volume in the CHO-5 trial was significantly different from WP. The performance data showed that in all of the CHO trials, significantly more work was produced compared to the WP trial (CHO-5 = 1.98 +/- 0.09 x 10(5) Nm vs WP = 1.83 +/- 0.11 x 10(5) Nm). There were no significant differences in performance between any of the CHO trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1988

Influence of sodium bicarbonate on sprint performance: relationship to dosage.

The purpose of this investigation was to determine the minimum oral dosage of bicarbonate needed to significantly elevate blood bicarbonate and the influence of induced alkalosis on performance in high-intensity, short-duration exercise. Nine endurance-trained cyclists performed four 2-min sprints on separate occasions using an isokinetic cycle ergometer (Fitron, Cybex, Inc.). One hour before each test, the cyclists consumed either a placebo (A), a solution of 0.10 g NaHCO3.kg-1 body weight (B), a solution of 0.15 g NaHCO3.kg-1 body weight (C), or a solution of 0.20 g NaHCO3.kg-1 body weight (D) in random order. Arterialized venous blood was taken before (PRE) and after (POST) ingestion, and 1, 3, 5, 10, and 15 min following the 2-min bike sprint. The results showed a significant increase in POST blood bicarbonate, and the elevation was incrementally related to the dosage. There was, however, no significant improvement in performance. Total work (mean +/- SE) for each treatment (N.m per 2 min) were: A, 47,267 (+/- 2,472); B, 47,004 (+/- 3,094); C, 46,312 (+/- 2,964); and D, 47,190 (+/- 2,621). The results of this study show that incremental doses of NaHCO3 of 0.20 g.kg-1 and below produce incremental elevations in blood bicarbonate but do not produce improvements in performance for a sprint bout lasting 2 min.

Acid-Base Equilibrium↗

PubMed1987

Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners.

The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners (VO2max = 68.2 +/- 3.4 ml X kg-1 X min-1). On three separate occasions, the runners performed a 30 min treadmill run at 70% VO2max. Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P less than 0.05) reaching peak levels at 30 min post-feeding (7.90 +/- 0.24 mmol X l-1). With the onset of exercise, glucose levels dropped to a low of 5.89 +/- 0.85 mmol X l-1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21 +/- 0.31 mmol X l-1 and 5.95 +/- 0.23 mmol X l-1 respectively, and were not significantly different (P less than 0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise.

Adult↗

PubMed1987

Muscle fiber composition and respiratory capacity in triathletes.

In an effort to describe the skeletal muscle characteristics of trained triathletes, biopsies were obtained from the gastrocnemius, vastus lateralis, and posterior deltoid muscles of 11 triathletes and 4 normally active controls. Each specimen was analyzed for muscle fiber composition, respiratory capacity (QO2), and citrate synthase activity. The mean (+/- SE) percentage of type I fibers for the triathletes was 59 (4.0), 63 (3.3), and 60 (2.8) in the gastrocnemius, vastus lateralis, and deltoid, respectively (P greater than 0.05). The mean (+/- SE) QO2 values in the gastrocnemius (4.4 +/- 0.3 ml O2.min-1.g-1) and the vastus lateralis (4.1 +/- 0.2) were not significantly different while the QO2 values of the deltoid (3.6 +/- 0.2) were significantly lower than the gastrocnemius (P less than 0.05). The mean citrate synthase activity of the deltoid (27.7 +/- 1.7 mumol.min-1.g-1) was significantly lower than both the vastus lateralis (36.0 +/- 3.2) and the gastrocnemius (45.8 +/- 2.1) (P less than 0.05). There was a high correlation between the percentage of type I fibers and the citrate synthase activity within the vastus lateralis (r = .760) and deltoid (r = .610) (P less than 0.05) but not the gastrocnemius (r = .200). No significant relationships were observed between skeletal muscle characteristics and VO2 max nor between skeletal muscle characteristics and performance. The results of this study demonstrate that: (1) these triathletes have a high percentage of type I fibers in all three muscle groups; (2) skeletal muscle characteristics were not highly related to laboratory or competitive performance;(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987

Muscle fiber composition and enzyme activities in elite female distance runners.

This study has attempted to describe the fiber composition and respiratory potential in the leg (gastrocnemius) muscle of highly trained, elite female distance runners. As noted, many of these women were competing successfully in middle-distance (1500-3000 m) rather than long distance (10 km and marathon) events. This fact appears to explain many of the differences observed between these "elite female runners" and the "elite male runners" studied in the 1975 Dallas study (6). With the exception of differences in muscle fiber areas, the female runners appear to show the same enzyme adaptations to endurance training that have been reported for male runners. The most notable finding of this study was the remarkable similarity of muscle fiber composition and enzyme activity for male and female runners when matched according to their preferred competitive distance.

Capillaries↗

PubMed1987

Substrate utilization in leg muscle of men after heat acclimation.

Eight men were heat acclimated (39.6 degrees C and 29.2% rh) for 8 days to examine changes in substrate utilization. A heat exercise test (HET), (cycling for 60 min; 50% maximal O2 consumption) was performed before (UN-HET) and after (ACC-HET) the acclimation period. Muscle glycogen utilization (67.0 vs. 37.6 mmol/kg wet wt), respiratory exchange ratio (0.85 +/- 0.002 vs. 0.83 +/- 0.001), and calculated rate of carbohydrate oxidation (75.15 +/- 1.38 vs. 64.80 +/- 1.52 g/h) were significantly reduced (P less than 0.05) during the ACC-HET. Significantly lower (P less than 0.05) femoral venous glucose (15, 30, and 45 min) and lactate (15 min) levels were observed during the ACC-HET. No differences were observed in plasma free fatty acid (FFA) and glycerol concentrations or glucose, lactate and glycerol arteriovenous uptake/release between tests. A small but significant increase (P less than 0.05) above resting levels in FFA uptake was observed during the ACC-HET. Leg blood flow was slightly greater (P greater than 0.05) during the ACC-HET (4.64 +/- 0.13 vs. 4.80 +/- 0.13 l/min). These findings indicate a reduced use of muscle glycogen following heat acclimation. However, the decrease is not completely explained by a shift toward greater lipid oxidation or increased blood flow.

Acclimatization↗

PubMed1987

Effect of pre-exercise carbohydrate feedings on endurance cycling performance.

Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 +/- 5.2 min, FRU = 90.6 +/- 12.4, and GLU = 92.8 +/- 11.3, mean +/- SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 +/- 0.34 mmol X l-1 at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 +/- 8.2 mmol X kg-1 wet weight, FRU = 56.3 +/- 3.0 mmol X kg-1 wet weight, GLU = 50.0 +/- 4.9 mmol X kg-1 wet weight) and total glycogen use (CON = 93.4 +/- 11.1, FRU = 118.8 +/- 10.9, and GLU = 99.5 +/- 4.3) were similar in the three trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987

Influence of selected carbohydrate drinks on cycling performance and glycogen use.

Eight well-trained male cyclists were used to determine the influence of carbohydrate feedings on exercise performance and muscle glycogen use. Two days prior to each trial, the subjects performed a 60-min "depletion ride" at 70% VO2max, which was followed by the ingestion of a high carbohydrate diet (approximately 500 g X -1). During the experimental trials, the men performed 2 h of cycling exercise and consumed 150 ml of 1 of 4 solutions at 24-min intervals. The drinks were: H2O (artificially flavored and sweetened); maltodextrin (5 g X 100 ml-1) and fructose (5 g X 100 ml-1); maltodextrin (7.7 g X 100 ml-1) and high fructose corn syrup (2.3 g X 100 ml-1); maltodextrin (3 g X 100 ml-1 and glucose (2 g X 100 ml-1). The amount of work completed during the four trials was not significantly different. Initial glycogen levels were high, and glycogen values were not significantly different at the beginning of exercise or at 90 min (185.35 +/- 3.26 and 91.93 +/- 3.39, respectively). Blood glucose was greater at 60 min in trial maltodextrin and glucose (5.70 +/- 0.36 mmoles X l-1), maltodextrin and high fructose corn syrup (6.05 +/- 0.54), and maltodextrin and fructose (6.03 +/- 0.42) compared to H2O (4.97 +/- 0.35) (P less than 0.05). Blood glucose remained elevated at 90 min during the maltodextrin and fructose and maltodextrin and high fructose corn syrup trials and at 120 min in the maltodextrin and fructose trial. No differences were observed between trials in blood lactate, serum glycerol, respiratory exchange ratio, or the subjects' perception of effort.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987

Changes in body water and electrolytes during heat acclimation: effects of dietary sodium.

In an effort to describe the influence of both high (HNA) and low (LNA) dietary sodium (399 vs. 98 mEq Na+ X d-1) on body fluids during heat acclimation (HA), nine untrained males underwent 8 d of HA twice (90 min treadmill walking, 5.6 km X h-1, 6% grade) in an environmental chamber (40.1 degrees C, 23.5% RH). Mean wholebody Na+ balance calculations indicated that HNA resulted in an increase of Na+ of $916 mEq per 8 days per subject, whereas LNA resulted in a relative Na+ deficiency of -230 mEq per 8 days per subject. Subjects exhibited typical HA adaptations of decreased heart rate (HR), decreased rectal temperature (Tre) during exercise, and an increase in resting plasma volume (PV) during both diets. Significant HNA vs. LNA differences (p less than 0.05) were observed in HR (days 3-5), Tre (days 3-6), PV (day 4), plasma osmolality (day 4), plasma Na+ (day 4), urine Na+ (days 2-8), and sweat Na+ (days 4 and 8). The between-diet differences in HR, Tre and PV were not detectable by the end of each dietary-exercise regimen. Needle biopsy samples (20-50 mg, lateral aspect of the gastrocnemius) indicated that muscle Na+ and muscle water were similar on all days, except day 9 when intracellular fluid expansion during LNA was noted. Change in body weight was not strongly correlated with delta PV (R2 = 0.47, 0.10) and neither osmotic forces nor plasma protein movements explained all PV shifts adequately.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1986

Effects of eight weeks of bicycle ergometer sprint training on human muscle buffer capacity.

This investigation was undertaken to determine whether human skeletal muscle buffer capacity (BCm) is affected by training. Eight untrained males participated in 8 weeks of sprint training on bicycle ergometers. Muscle biopsy samples were taken from the vastus lateralis before and at several times following an incremental bicycle ergometer test (0 min, 5 min, 15 min). These subjects were tested before (PRE) and following (POST) the training period. Seven endurance-trained cyclists (ET) were also tested for the purpose of comparing the BCm of ET to that of PRE and POST. Biopsy samples were quick-frozen in liquid nitrogen and later analyzed for lactate concentration (HLam), homogenate pH (pHm), and creatine phosphate concentration. BCm was calculated from the change in HLam and pHm observed from rest to exhaustion and was expressed as mmol X kg-1 X pH-1 (Slykes). There was no significant difference in resting HLam or resting pHm among the groups. There was a significant difference in HLam at exhaustion between PRE (21.41 +/- 1.65 mmol X kg-1), POST (25.61 +/- 2.38 mmol X kg-1), and ET (11.16 +/- 0.31 mmol X kg-1) but no significant difference in pHm at exhaustion between PRE (6.65 +/- 0.03 pH units) and POST (6.69 +/- 0.06 pH units). pHm at exhaustion for the ET group was significantly higher than the others at 6.91 +/- 0.02 pH units. A significant difference between PRE and POST BCm was found (PRE: 44.68 +/- 3.03 S1; POST: 61.04 +/- 4.11 S1) while ET BCm (47.21 +/- 7.26 S1) was not significantly different from PRE. These data indicate that muscle buffer capacity is increased with highly intense sprint training but provide no evidence to suggest that muscle buffer capacity is affected by endurance training.

Adult↗

PubMed1986

Glucose feeding and exercise in trained rats: mechanisms for glycogen sparing.

This investigation studied the effect of an oral glucose feeding on glycogen sparing during exercise in non-glycogen-depleted and glycogen-depleted endurance-trained rats. The non-glycogen-depleted rats received via a stomach tube 2 ml of a 20% glucose solution labeled with [U-14C]glucose just prior to exercise (1 h at 25 m/min). Another group of rats ran for 40 min at higher intensity to deplete glycogen stores, after which they received the same glucose feeding and continued running for 1 h at 25 m/min. The initial 40-min run depleted glycogen in heart, skeletal muscle, and liver. In the non-glycogen-depleted rats the glucose feeding spared glycogen in the liver, primarily from the oxidation of blood-borne glucose in muscle. In the glycogen-depleted rats, muscle glycogen was repleted after the feeding, but sources other than the administered glucose also contributed to glycogen synthesis. The results suggest that glycogen depletion rather than the glucose feeding per se stimulates glycogen resynthesis in muscle during exercise in endurance-trained rats.

Animals↗