Lipoprotein lipase activity in skeletal muscle and adipose tissue of marathon runners after simple and complex carbohydrate-rich diets

A comparison of the influence of simple and complex carbohydrate (CHO) consumption on adipose tissue- and skeletal muscle-lipoprotein lipase activity (AT-LPLA, SM-LPLA) was examined. Twenty male marathon runners were divided into two equal dietary groups: simple-CHO and complex-CHO. Half of the subjects in each group consumed either a low-CHO (15% energy [E] intake), or a mixed diet (50% CHO) for 3 days. Immediately following this dietary period, the subjects consumed a CHO-rich diet (70% E intake) predominant in simple-CHO or in complex-CHO for an additional 3 days. Thereafter, all subjects returned to a normal mixed diet. Skeletal muscle biopsies, adipose tissue aspirations, and venous blood samples were obtained prior to dietary manipulation (PRE), upon completion of the 6 day diet (POST I), and 2 weeks after returning to a normal diet (POST II). The samples were analysed for AT-LPLA, SM-LPLA, serum insulin, and free fatty acids (FFA), and blood glucose, and lactate. SM-LPLA fell 71% from PRE values of 0.39 +/- 0.30 mu mol.g-1.h-1 to POST I values of 0.11 +/- 0.09 mu mol.g-1.h-1 (means +/- SD) (p less than 0.05), after a complex-CHO diet. However, the simple-CHO diet did not alter SM-LPLA. AT-LPLA similarly decreased (p less than 0.05) after the complex-CHO diet, and no significant decrease was noted after the simple-CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired muscle glycogen resynthesis after a marathon is not caused by decreased muscle GLUT-4 content

Asp, Sven, Thomas Rohde, and Erik A. Richter. Impairedmuscle glycogen resynthesis after a marathon is not caused by decreasedmuscle GLUT-4 content. J. Appl.Physiol. 83(5): 1482-1485, 1997.Our purpose wasto investigate whether the slow rate of muscle glycogen resynthesisafter a competitive marathon is associated with a decrease in the totalmuscle content of the muscle glucose transporter (GLUT-4). Sevenwell-trained marathon runners participated in the study, and musclebiopsies were obtained from the lateral head of the gastrocnemiusmuscle before, immediately after, and 1, 2, and 7 days after themarathon, as were venous blood samples. Muscle GLUT-4 content wasunaltered over the experimental period. Muscle glycogen concentrationwas 758 ± 53 mmol/kg dry weight before the marathon anddecreased to 148 ± 39 mmol/kg dry weight immediately afterward.Despite a carbohydrate-rich diet (containing at least 7 gcarbohydrate · kg bodymass¹ · day¹),the muscle glycogen concentration remained 30% lower than before-race values 2 days after the race, whereas it had returned to before-race levels 7 days after the race. We conclude that the total GLUT-4 proteincontent is unaltered in the lateral gastrocnemius after a competitivemarathon and that the slow recovery of muscle glycogen after the raceapparently involves factors other than changes in the total content ofthis protein.

     

Skeletal muscle creatine kinase MB alterations in women marathon runners

Total creatine kinase (CK) and CK MB activities were determined in gastrocnemius muscle and serum obtained from 14 female marathon runners. The level of CK MB in muscle increased significantly (p less than 0.05) after chronic exercise training from 5.3% to 10.5% of the total CK activity, but not after acute exercise (post-marathon 8.9%). No significant differences in total CK activities were detected. However, the total CK activity in the muscles were significantly (p less than 0.05) less than those previously reported from the muscle of men runners (1800 U/g, 3000 U/g respectively). No significant correlation existed between fiber type and muscle CK MB activity. Additionally, trace amounts of mitochondrial CK and CK BB were present in muscle homogenates. A significant correlation was observed in the increase in mean serum total CK (597 UL-1) and CK MB (23 UL-1) activities 24 h after the race (r = 0.97, p less than 0.05). These results suggest that gastrocnemius muscle in women adapts to training with increased CK MB activities and imply that skeletal muscle is the major source of elevated serum CK MB activities in women marathon runners.     

Skeletal muscle lactate dehydrogenase isozyme alterations in men and women marathon runners

Total lactate dehydrogenase (LD) and LD isozyme activities in gastrocnemius muscle from trained men and women runners were measured in response to the chronic stress of training for a marathon race (42.2 km). Following 9 wk of training, total LD activity in skeletal muscle from men and women runners significantly (P less than 0.02) decreased 2.26 and 2.25 U/mg protein, respectively. However, men's total LD activities were significantly (P less than 0.001) less than the women's both before and after training. Significant (P less than 0.05) increases in LD1 activities in skeletal muscle in men and women runners were also observed after training. No significant correlations were detected between percent fiber type composition in men or women vs. the changes in total LD activity, changes in LD1 activity, maximal O2 consumption or training distance averaged per week after the training period. The biochemical adaptations in skeletal muscle that occurred in the LD isozyme composition in both men and women runners make the runners skeletal muscle appear similar to heart muscle in LD1 and LD2 activities.     

Carbohydrate ingestion and muscle glycogen depletion during marathon and ultramarathon racing

Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption (VO2max) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500-600 g.day-1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO.h-1 during competition; (ii) that neither the amount (10 g vs 40 g.h-1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km.     

Creatine kinase-MB isoenzyme adaptations in stressed human skeletal muscle of marathon runners

The creatine kinase (CK) isoenzyme composition was determined in serial gastrocnemius muscle biopsies obtained from 12 male marathon runners. The mean muscle CK-MB composition significantly increased after chronic exercise (training) from 5.3% (pretraining) to 7.7% (premarathon) as well as after acute exercise (postmarathon) to 10.5% of the total CK activity (P less than 0.05). However, no significant differences in total CK activities were detected. Additionally, mitochondrial CK and CK-BB isoenzymes were present in muscle homogenates. A significant correlation was observed in the increase in mean serum total CK (3,322 U/l) and CK-MB (174 U/l) activities 24 h after the race (r = 0.98, P less than 0.05). These results show that gastrocnemius muscle adapts to long-distance training and racing with increased CK-MB activities and imply that skeletal muscle is the major source of elevated serum CK-MB activities in marathon runners.     

Dehydration and serum biochemical changes in marathon runners

The effects of a competitive marathon race on serum biochemical and haematological parameters have been evaluated. Blood samples were obtained shortly before and immediately after the race; urine samples were also obtained before and after the race. Body weight was recorded pre- and post-race. During the race subjects consumed a total of 1.41 of either water or a dilute glucose-electrolyte solution. The average weight loss of the runners was 2.09 +/- 0.77 kg (mean +/- SD), corresponding to 2.9 +/- 0.8% of body weight. Small but significant increases in both haematocrit and haemoglobin concentration occurred; plasma volume was calculated to decrease by 4.7%. Serum potassium concentration showed no change, but the response was highly variable; serum sodium concentration increased in line with the decrease in plasma volume. In the group of subjects drinking water during the race, the pre-race plasma glucose concentration was 5.3 +/- 1.2 mmol . l-1, this was unchanged after the race (5.0 +/- 1.2 mmol . l-1). A significant increase (P less than 0.01) in the plasma glucose concentration, from 5.2 +/- 0.6 to 6.0 +/- 1.5 mmol . l-1 occurred in the group of subjects drinking the glucose-electrolyte solution. Apart from this, there were no significant differences between the two groups.     

Hepatopancreas gluconeogenesis and glycogen content during fasting in crabs previously maintained on a high-protein or carbohydrate-rich diet

The present study assessed the effect of different fasting times on the in vitro gluconeogenic capacity of Chasmagnathus granulata crabs previously adapted to a high-protein (HP) or carbohydrate-rich (HC) diet using the incorporation of [U-(14)C]l-lactate or [U-(14)C]l-alanine into glucose. We also recorded haemolymphatic glucose and hepatopancreatic glycogen levels. In the HP group, on the third day of fasting there were decreases in the synthesis of glucose from (14)C-alanine and in haemolymph glucose. After 15 days of fasting, haemolymph glucose and hepatopancreatic glycogen levels were maintained by an increase in the conversion of (14)C-alanine into glucose. However, after 21 days of fasting the gluconeogenic capacity was decreased and hepatopancreas glycogen concentration was reduced. In the HC group, hepatopancreatic glycogen was the energy source during the first 6 days of fasting. Gluconeogenesis from (14)C-lactate decreased after 6 days of fasting, remaining low until 21 days of fasting. The conversion of (14)C-alanine into glucose was increased after 15 days fasting and hepatopancreatic glycogen was raised in relation to that present after a 6-day fasting. In both dietary groups the stabilization in the levels of haemolymph glucose after 21 days fasting may result from a reduction in metabolic rate during restricted feeding.     

Effects of weather on the performance of marathon runners

The effects of air temperature, relative and specific humidity, wind speed, solar shortwave radiation, thermal longwave radiation, and rain on the performance of participants in the annual Stockholm Marathon from 1980 to 2008 were analysed statistically. The objective was to validate and extend previous studies by including data on finishing times of slower male and female runners and on the percentage of non-finishers. Due to decadal trends in the finishing time not related to weather, the finishing time anomaly (FTA) was calculated as the deviation of the annual finishing time from the linear trend of the finishing time. In all categories of runners, the single weather parameter with highest correlation with the FTA was the air temperature (correlation coefficient r = 0.66–0.73, with the highest values for slowest runners). Also, the solar shortwave radiation (r = 0.41–0.71), air relative humidity (r = −0.57 to −0.44) and, for male runners, the occurrence of rain (r = −0.51 to −0.42) reached a statistically significant correlation with the FTA, but the effects of the relative humidity and rain only arose from their negative correlation with the air temperature. The percentage of non-finishers (PNF) was significantly affected by the air temperature and specific humidity (r = 0.72 for multiple regression), which is a new result. Compared to faster runners, the results of slower runners were more affected by unfavourable weather conditions; this was previously known for runners with finishing times of 2.1–3 h, and now extended to finishing times of 4.7 h. Effects of warm weather were less evident for female than male runners, which was probably partly due to female runners’ larger ratio of surface area to body mass and slower running speed.     

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.     

Physiological differences between black and white runners during a treadmill marathon

To determine why black distance runners currently out-perform white distance runners in South Africa, we measured maximum oxygen consumption (VO2max), maximum workload during a VO2max test (Lmax), ventilation threshold (VThr), running economy, inspiratory ventilation (VI), tidal volume (VT), breathing frequency (f) and respiratory exchange ratio (RER) in sub-elite black and white runners matched for best standard 42.2 km marathon times. During maximal treadmill testing, the black runners achieved a significantly lower (P less than 0.05) Lmax (17 km h-1, 2% grade, vs 17 km h-1, 4% grade) and VI max (6.21 vs 6.82 l kg-2/3 min-1), which was the result of a lower VT (101 vs 119 ml kg-2/3 breath-1) as fmax was the same in both groups. The lower VT in the black runners was probably due to their smaller body size. The VThr occurred at a higher percentage VO2max in black than in white runners (82.7%, SD 7.7% vs 75.6%, SD 6.2% respectively) but there were no differences in the VO2max. However, during a 42.2-km marathon run on a treadmill, the black athletes ran at the higher percentage VO2max (76%, SD 7.9% vs 68%, SD 5.3%), RER (0.96, SD 0.07 vs 0.91, SD 0.04) and f (56 breaths min-1, SD 11 vs 47 breaths min-1, SD 10), and at lower VT (78 ml kg-2/3 breath-1, SD 15 vs 85 ml kg-2/3 breath-1, SD 19). The combination of higher f and lower VT resulted in an identical VI.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cholecystokinin, gastrin and stress hormone responses in marathon runners.

The purpose of this investigation was to determine the influence of long-distance running on the secretion of the gastrointestinal peptide hormones cholecystokinin (CCK) and gastrin. Several known stress hormones, ACTH, cortisol and norepinephrine, were also measured. The hormones were estimated before and after a competitive marathon run of 46.5 km and under control conditions a few weeks later. Except gastrin, all hormones were significantly higher under prerun conditions than under control conditions and were highest after the run. The most marked prerun elevation was in CCK. Therefore, CCK seems to be an important regulation factor in response to anticipatory stress.     

Effect of muscle glycogen content on exercise-induced changes in muscle T2 times

Effects of gastrocnemius glycogen (Gly)concentration on changes in transverse relaxation time (T2; ms) werestudied after 5-min plantar flexion at 25% of maximum voluntarycontraction (MVC). Gastrocnemius Gly, phosphorus metabolites, and T2were measured in seven subjects by using interleaved¹³C/³¹Pmagnetic resonance spectroscopy (MRS) at 4.7 T and magnetic resonanceimaging (MRI; 1.5 T). After baseline MRS/MRI, subjects exercised for 5 min at 25% of MVC and were reexamined (MRS/MRI). Subjects thenperformed ~15 min of single-leg toe raises (50 ± 2% of MVC),depleting gastrocnemius Gly by 43%. After a 1-h rest (for T2 return tobaseline), subjects repeated the 5-min protocol, followed by a finalMRI/MRS. After the initial 5-min protocol, T2 values increased by 5.9 ± 0.8 ms (29.9 ± 0.4 to 35.8 ± 0.6 ms), whereas Gly did notchange significantly (70.5 ± 6.8 to 67.6 ± 7.4 mM). After 15 min of toe raises, gastrocnemius Gly was reduced to 40.4 ± 5.3 mM(P  0.01), recovering to 45.8 ± 5.3 mM (P  0.05) during a 1-h rest.After the second 5-min bout of plantar flexion (reduced Gly at 25% ofMVC), T2 values increased by 5.0 ± 0.8 ms (30.4 to 35.4 ms),whereas muscle Gly rose to 57.6 ± 5.3 mM. We conclude that muscleGly concentration per se does not affect exercise-induced T2 increasesin the human gastrocnemius.

     

Adrenaline-mediated glycogen phosphorylase activation is enhanced in rat soleus muscle with increased glycogen content

The effect of glycogen content on the activation of glycogen phosphorylase during adrenaline stimulation was investigated in soleus muscles from Wistar rats. Furthermore, adrenergic activation of glycogen phosphorylase in the slow-twitch oxidative soleus muscle was compared to the fast-twitch glycolytic epitrochlearis muscle. The glycogen content was 96.4 +/- 4.4 mmol (kg dw)(-1) in soleus muscles. Three hours of incubation with 10 mU/ml of insulin (and 5.5 mM glucose) increased the glycogen content to 182.2+/-5.9 mmol (kg dw)(-1) which is similar to that of epitrochlearis muscles (175.7+/-6.9 mmol (kg dw)(-1)). Total phosphorylase activity in soleus was independent of glycogen content. Adrenaline (10(-6) M) transformed about 20% and 35% (P < 0.01) of glycogen phosphorylase to the a form in soleus with normal and high glycogen content, respectively. In epitrochlearis, adrenaline stimulation transformed about 80% of glycogen phosphorylase to the a form. Glycogen synthase activation was reduced to low level in soleus muscles with both normal and high glycogen content. In conclusion, adrenaline-mediated glycogen phosphorylase activation is enhanced in rat soleus muscles with increased glycogen content. Glycogen phosphorylase activation during adrenaline stimulation was much higher in epitrochlearis than in soleus muscles with a similar content of glycogen.     

Melatonin increases muscle and liver glycogen content in nonexercised and exercised rats

The effects of melatonin on several parameters of carbohydrate and lipid metabolism were investigated in exercised and nonexercised rats. Animals were run to exhaustion on a rodent treadmill at 24 m/min and a 12% slope. Exercise resulted in a significant hypoglycemia and increased plasma levels of lactate and beta-hydroxybutyrate, together with a significant reduction of glycogen in muscle and liver. Muscle and liver glycogen content was elevated and plasma free fatty acid decreased in nonexercised animals receiving melatonin (0.5 or 2.0 mg/kg i.p). Melatonin at 2.0 mg/kg reduced plasma lactate and increased lactate concentration in liver. When compared to untreated exercised animals glycemia and muscle and liver glycogen content were significantly higher in melatonin-treated exercised animals, while plasma and liver lactate and plasma beta-hydroxybutyrate were significantly reduced. Our data indicate that melatonin preserves glycogen stores in exercised rats through changes in carbohydrate and lipid utilization.     

Alterations in plasma-volume-corrected blood components of marathon runners and concomitant relationship to performance

The study was undertaken to determine the effects of running a marathon on concentration of various blood components resulting from phenomena other than fluid loss, and these were related to performance times. Twenty male marathon runners ranging from 20 to 50 years of age participated in the study. Blood samples were collected before and after the subjects ran in a marathon. Blood samples were analyzed for sodium, potassium, glucose, lactate dehydrogenase, creatinine, creatine phosphokinase, triglycerides, cholesterol, hematocrit, hemoglobin, protein, white blood cell number, uric acid, carbon dioxide, and iron. All of the blood parameters increased significantly in concentration with the exceptions of glucose and carbon dioxide which decreased. After accounting for plasma-volume loss (COR), there remained significant increases in blood serum lactate dehydrogenase, creatinine, creatine phosphokinase, uric acid, iron, and whole-blood white blood cell number. Significant decreases in COR serum sodium, protein, glucose, and carbon dioxide were found. Lactate dehydrogenase and creatine phosphokinase concentration changes support the concept of acute damage to muscle tissue resulting from marathon running. No strong relationship between performance time and other measured variables was found. COR measures were more representative of marathon induced blood changes from physiological dynamics other than plasma volume change than presently reported findings.