European Journal of
Applied
Eur. J. Appl. Physiol. 41, 101-108 (1979)
Physiology
and Occupational Physiology 9 Springer-Verlag 1979
Metabolic Adaptation to Prolonged Exercise K. Scheele, W. Herzog, G. Ritthaler, A. Wirth, and H. Weicker Institute of Pathophysiology and Sports Medicine University of Heidelberg, D-6900 Heidelberg, Federal Republic of Germany and Institute of Sports Medicine, D-7000 Stuttgart, Federal Republic of Germany
Summary. A study was undertaken to evaluate and to examine the role of substrate supply in 50 healthy subjects after long distance events, such as 10 km, 25 km, and marathon races. The metabolic, variables of carbohydrate metabolism were greatest in 10-km runners, with the highest increase in glucose, lactate, and pyruvate, while in marathon runners only moderate changes were observed. Marathon competitors gave the greatest decrease in insulin concentration whereas glucagon and cortisol showed a contrary tendency. As for lipid concentrations, the most remarkable point was that after the marathon competition the best runners had the highest increase in free fatty acids; the longer the race, the higher were the/3-hydroxybutyrate and acetoacetate levels after the competition. It is important to emphasize that the limiting factor up to 90 min duration is the competitor's ability to deplete the stores of glycogen. Beyond 90 rain (or 25 kin) the decrease in insulin, the rise in cortisol and the higher concentration of ketnne bodies found indicate a change in metabnlic response. Key words: Prolonged exercise - Hormones - Lipolysis metabolism
Carbohydrate
Since 1922 maximal oxygen consumption has been considered as the main fimiting factor of physical capacity (Hill, 1922). In spite of the development of detailed and more definite methods of examining an athlete or a patient, the rate of maximal oxygen consumption has maintained its central position. Spiroergometric resarch and tests on bycycles and treadmills determine the capacity of individual endurance. The most important limiting factors in analysing oxygen consumption and oxygen absorption capacity are perfusion of the respiratory system, cardiac output, blood volume, and total hemoglobin (Hollmann, 1975). On the other hand it is now well Offprint requests to: PD Dr. K. Scheele, Taubenheimstr. 8, D-7000 Stuttgart 50, Federal Republic of Germany
0301-5548/79/0041/0101/$ 01.60
102
K. Scheele et al:
documented that the oxidative capacity in skeletal muscle limits both the intensity and duration o f work (Holloszy, 167). Recent studies have demonstrated that the level of phosphates and glycolytic c a p a c i t y play an important role in the substrate supply o f exercising skeletal muscles during short-term exercise. Skeletal muscle is regarded as a large depot of substrates as well as a place of high utilization of substrates during prolonged physical exercise (Wahren, 1971). U p to 3 min of performance, the energy of muscle contractions is obtained mainly from creatine-phosphate, b y anaerobic depletion of glucose and glycogen, and b y the disposal of adenosine-triphosphate. During this short period, elasticity and frequency of muscle contractions are the limiting factors in physical performance. During long-term exercise aerobic c a p a c i t y becomes important and is determined mainly b y the substrate supply of glucose, free fatty acids, amino acids, and the capacity of enzymes o f the respiratory chain (Holloszy, 1967; Ahlborg, 1974; Hollmann, 1975; Weicker, 176). This study was undertaken to evaluate and to examine the role of substrate supply after extensive prolonged exercise, during long distance events such as 10 km, 25 km, and m a r a t h o n races.
Subjects and Methods
Subjects The metabolic parameters before and after prolonged exercise were examined in 50 healthy subjects. The subjects were classified into groups of 22 subjects over 10 km (17 men, aged 33-49, 5 women, aged 34-56), 11 subjects over 25 km (10 men, aged 32-57, 1 women, aged 41) and 17 marathon runners (14 men, aged 30-63, 3 women, aged 30-63). None of these athletes had a history or evidence of liver disease or other metabolic disorder. Data concerning age, height, and weight were recorded before the competition (average weight of men 73.2 kg, of women 59.8 kg, average height of men 173.5 cm, of women 166,4 cm). All subjects had participated only in occasional training programs beforehand. The 50 subjects may be regarded as moderately trained subjects (ca. 30 min gymnastics per week on average). They were informed of the nature, purpose, and possible risks involved in the study before agreeing to participate.
Methods All athletes were examined 30 min before the competition. Blood samples were obtained by inserting a short catheter into the anticubital vein. This procedure was repeated directly after the end of the competition. Total blood loss during these two procedures was less than 50 ml.
Analysis Blood glucose was determined enzymatically (oxidase -- peroxidase method) with a Beckmann glucose analyzer, lactate and pyruvate (whole blood) by biochemical analysis, and the remaining blood was centrifuged, and aliquots stored at - 2 0 ~ C for further usage. The concentrations of insulin, glucagon, and eorfisol were determined by radio-immunoassay (RIA), insulin after Starr and Rubenstein (1974),
Metabolic Adaptation to Prolonged Exercise
103
using Boehringer Monotest-Insulin, glucagon according to Faloona and Unger (1974) using the kit of toe Novo Research Institute, Bagsvaerd, Denmark, cortisol according to the method of Vecsei (1974), Heidelberg, Pharmakol. Inst. Glycerol and triglycerides were also determined enzymatically, whereas the concentration of free fatty acids was analyzed by titrimetric determination (Wirth et al., 1976). Aceto-acetate and /3-hydroxybutyrate were analyzed by enzymatic fluorimetric micromethods, the determination of urea and creatinine being also analyzed enzymaticallyby a biochemicaltest combination (Boehringer, Mannheim).
Calculation Data in the text, tables, and figures are given as means • SD. Standard statistical methods had been employed, using the paired t-test.
Results Table 1 shows the pre- and post-competition values of glucose, lactate, and pyruvate according to the distance performed. The 10-km athletes increased their contration of glucose by 42.8 mmol/1., the 25-km runners increased by 24.6 mmol/1., and after the m a r a t h o n competition there was no increase at all. Analyzing these results in detail showed that the 3 best athletes had the highest glucose and lactate concentrations after performance. These athletes with the supraphysiological glucose values and highest lactate concentrations did not differ in any other way from the rest of the group. Table 2 shows the concentration of hormones (insulin, glucagon, cortisol). A decrease in insulin concentration of 38. 8 pmol/1 for the 10-km runners, of 36.7 pmol/1 for the 25-km runners, and of 70.1 pmol/1 for the m a r a t h o n runners was observed. The glucagon and cortisol concentrations showed a contrary tendency: the longer the distance, the higher the glucagon and cortisol values (insulin antagonistic hormones).
Table 1. The concentration of blood glucose, lactate, and pyruvate according to performed distance Before
After
Difference
P values
Glucose (mmol/1) 10 km 25 km Marathon
4.81 + 1.02 4.48 _+0.99 5.38 + 1.09
6.87 + 3.51 5.58 + 0.81 5.40 • 1.19
+ 42.8 + 24.6 + 0.4
< 0.01 < 0.01 n.s.
Lactate (mmo~l) 10 km 25 km Marathon
1.59 • 0.67 1.45 _+0.40 1.70 + 0.59
4.31 + 1.34 3.33 + 1.27 2.69 • 0.77
+ 171.1 + 125.0 + 58.2
< 0.001 < 0.001 < 0.001
Pyruvate (mmol/1) 10 km 25 km Marathon
0.063 _+0.025 0.074 + 0.020 0.067 + 0.028
0.192 + 0.077 0.184 + 0.060 0.166 _+0.057
+ 204.8 + 148.6 + 147.8
< 0.001 < 0.001 < 0.001
104
K. Scheele et al.
Table 2. The changes of blood hormone concentration with regard to performed distance Before
After
Difference
P values
Insulin (pmol/1) 10 km 25 km Marathon
116.7 + 106.3 123.0 + 92.1 263.0 + 217.5
71.4 + 68.3 77.8 _+ 45.2 78.6 • 43.7
- 38.8 - 36.7 - 70.1
< 0.05 n.s. < 0.001
Glucagon (pmol/1) 10 km 25 km Marathon
10.62 _+ 7.17 18.36 + 15.49 30.99 + 12.34
13.20 + 8.32 28.12 + 14.92 78.62 _+ 34.15
+ 24.3 + 53.2 + 153.0
n.s. n.s. < 0.001
Cortisol (pmol/1) 10 km 25km Marathnn
0.276 + 0.120 0.261+0.122 0.316 + 0.145
0.407 + 0.156 0.435+0.160 0.553 + 0.274
+ 47.5 +60.5 + 75.0
< 0.001 < 0.001 < 0.001
Table 3. The changes of lipid values with regard to the distance of running Before
After
Difference
P values
Triglycerides (mmol/1) 10 km 1.181 + 0.649 25 km 1.093 + 0.465 Marathon 1.432 + 0.614
0.791 _+0.434 0.678 _+ 0.501 0.689 _+ 0.646
-- 33.0 - 38.0 51.9
n.s.
Glycerol (mmol/1) 10 km 25 km Marathon
0.554 + 0.273 0.914 + 0.343 0.962 + 0.513
+ 166.4 + 345.9 + 403.7
< 0.001 < 0.001 < 0.001
954.4 _+ 393.6 1354.5 + 480.2 1805.5 + 491.6
+ 118.9 + 193.3 + 291.1
< 0.001 < 0.001 < 0.001
0.208 + 0.118 0.205 + 0.120 0.191 _+ 0.111
Free fatty acids (~val/1) 10 km 436.1 + 130.0 25 km 461.8 + 151.7 Marathon 461.6 + 167.3
-
n.s.
< 0.001
T h e c h a n g e s o f lipid values w i t h r e g a r d t o t h e d i s t a n c e c o v e r e d are s h o w n in T a b l e 3. All r u n n e r s s h o w e d a d e c r e a s e in t r i g l y c e r i d e c o n c e n t r a t i o n a f t e r t h e c o m petition, 33.0 m m o l / 1 for t h e 1 0 - k m r u n n e r s , 38.0 m m o l / 1 f o r t h e 2 5 - k i n r u n n e r s , a n d 51.9 m m o l / 1 f o r t h e m a r a t h o n r u n n e r s . T h e g l y c e r o l c o n c e n t r a t i o n s h o w e d a n inc r e a s e o f 166.4 m m o l / l for t h e 1 0 - k i n r u n n e r s , a n i n c r e a s e o f 3 4 5 . 9 m m o l / 1 for t h e 2 5 - k m r u n n e r s , a n d o f 4 0 3 . 7 m m o l / 1 for t h e m a r a t h o n r u n n e r s . A f t e r p e r f o r m a n c e , t h e 1 0 - k m a t h l e t e s s h o w e d a n i n c r e a s e o f 118.9 Cmol/1 in t h e free f a t t y acids, t h e 2 5 - k m r u n n e r s o f 193.3, a n d t h e m a r a t h o n r u n n e r s a n i n c r e a s e o f 291.1 ~mol/1. The concentrations of hydroxybutyrate and acetoacetate rose during exercise a n d t h e r e w a s a t e n d e n c y for t h e levels t o rise m o r e w i t h i n c r e a s e in d i s t a n c e (see T a b l e 4).
Metabolic Adaptation to Prolonged Exercise
105
Table 4. The blood concentration of/3-hydroxybutyrate and acetoacetate according to the distance covered Before
After
Difference
P values
0.180 + 0.054 0.225 + 0.099 0.236 _+0.100
0.511 _+0.231 0.789 + 0.371 0.867 +_0.479
+ 183.9 + 250.7 + 367.4
< 0.001 < 0.001 < 0.001
Acetoacetate (mmol/1) 10 km 0.013 + 0.013 25 km 0.015 _+0.020 Marathon 0.008 + 0.009
0.040 _+0.026 0.071 + 0.034 0.073 + 0.039
+ 207.7 + 373.3 + 312.5
< 0.001 < 0.001 < 0.001
Hydroxybutyrate (mmol/1) 10 km 25 km Marathon
Table 5. The changes of blood urea and creatinine values according to distance covered Before
After
Difference
P values
Creatinine (~mol/1) 10 km 25 km Marathon
80.5 _+ 11.5 78.7 + 10.6 75.1 + 15.0
76.0 _+ 14.1 101.7 _+ 19.5 121.1 _+21.2
- 5.6 + 29.2 + 61.3
n.s. < 0.001 < 0.001
Urea (mmol/1) 10 km 25 km Marathon
7.03 _+ 1.38 6.89 + 1.41 6.73 _+ 1.49
7.09 _+ 1.35 7.59 + 1.46 9.09 _+ 1.53
+ 1.0 + 10.2 + 35.1
n.s. n.s. < 0.001
The different concentrations of urea and creatinine according to running distance can be seen in Table 5: (a) Creatinine: The 10-km runners show a decrease of 5.6, the 25-km runners an increase of 29.2, and the m a r a t h o n runners an increase of 61.3 ~mol/1. (b) Urea: After the competition, no changes could be discovered for the 10-km runners, where as the 25-km runners showed an increase of 35.1 ~mol/1.
Discussion The results of these investigations show the interdependency of the concentration a n d / o r absorption capacity of the different substrates and the physical capacity of the subjects tested under various conditions (long-distance running over 10 km, 25 km, and marathon). In detail we have to scrutinize the different metabolic ways and parameters influencing and limiting the oxidative capacity of the exercising muscle during and after prolonged sporting activity. I n agreement with findings from previous studies we found that the glucose concentration rises after prolonged exercise (Randle, 1963; R u d e r m a n n , 1969; Sen-
106
K. Scheele et al.
ger, 1977; see Table 1). There are two remarkable points in these results: The longer the running distance, the lower the increase in glucose. The best runners of the 10km group had the highest glucose and lactate concentration as well as the highest insulin level. It is also noteworthy that after-performance values reach supraphysiological values. Thus our findings support the hypothesis that the aerobic and oxidative requirement of a 60 rain sporting activity such as a 10-km run is a suitable way of depleting the stores of glycogen in exercising muscle and in the liver. As the glycogen stores are depleted by prolonged exercise, the concentration of insulin decreases (Table 2): the longer the exercise, the lower the insulin concentration after performance. In this context it is of interest to note the hypothesis that gluconeogenesis by amino acids has become an important factor (Young, 1967; Rudermann, 1975). On the other hand the possibility of direct oxidation and utilization of lipids is also present (Senger, 1977). In theory, the connection between carbohydrate and lipid metabolism during and after prolonged exercise depends on three circumstances: (1) Intensity, type, and duration of muscular exercise. (2) Nutrition of the athlete. (3) Metabolic adaption. As to the first point, we can see a close connection between glucose concentration and type of performance. After having finished the 10-kin distance, the runners showed an increase in lactate and pyruvate, and the limiting factor of performance is the lactogen - oxygen efficiency, whereas during a run over the marathon distance triglycerides, free fatty acids, and the metabolic response in form of ketone bodies plays a limiting role. The increased oxidation of free fatty acids and the utilization of triglycerides during and after the marathon - seen in the results of the 25-km and marathon runners - includes a block in glucose uptake and utilization by the peripheral muscle. This hypothesis was put forward by Randle (1970). These data show a constant rise in free fatty acids and ketone bodies for the 25-km and even more for the marathon runners; so the most important conclusion of these results is the shift in metabolism from glycogen to lipid oxidation after covering a distance of 25 km. With respect to the decrease in insulin concentration by prolonged exercise it is of interest to note that there is a parallel progressive increase in glucagon and cortisol (Table 4). A decrease in insulin concentration during prolonged exercise has been reported, and is wellknown (Berger, 1975). But there are only few investigations with regard to the period of performance. Our results show the changes in metabolic and hormonal adaptions in a typical way: the longer the distance and time of performance, the higher the concentration of glueagon and cortisol (insulin antagonistic hormones, see Table 2). The increase in glucagon seen in the present study is comparable to the metabolic changes during starvation (Ahlborg et al., 1974). On the other hand, we can assume that there are two effects of the stimulatory influence of glucagon and cortisol: (1) A higher output of hormones stimulating lipolysis, thereby making available to the liver increased quantities of glycerol and free fatty acids. (2) The stimulatory influence of glucose precursors and gluconeogenesis which has been demonstrated elsewhere (Ahlborg et al., 1974). According to Ahlborg (1974) and Senger (1977), an increased hypoxia of muscle tissue is responsible for the insulin clearance during prolonged exercise such as a
Metabolic Adaptation to Prolonged Exercise
107
25-km run and marathon. In addition, we can discuss a factor similar to insulin which is produced in prolonged-exercise muscle tissue and causes the increased utilization of glucose in working muscle (Goldstein, 1953, Dieterle, 1973). By means of these data and results we can fairly assume that performed endurance exercise such as long-distance running results in an economic working of metabolism, i.e., a rise in lipolytic capacity, a higher peripheral utilization of glucose, and an increased uptake of glucose precursors causing an acceleration of gluconeogenetic processes (Wahren, 1971). Variation in the individual characteristics of the runners, including the time of the last meal, and differences in the intake of carbohydrates, amino acids, fats, and minerals m a y well be responsible for the large range of values observed before the competition. As to changes in creatinine and urea levels (Table 5) we suggest that these m a y be caused by the muscle cell: the longer the performed exercise, the higher the concentration of creatinine. Thus the highest creatinine concentration occurred after the marathon competition. In the same way we assume that the higher concentration of urea after the marathon competition reflects the restoration of glycogen stores by gluconeogenetic processes. These findings suggest that we should observe the values of branched-chain amino acids in blood samples, and would expect to find the highest values in the best marathon runners. These data will be published later. The results clearly show that the performance of long distance events such as 10 km, 25 km, and marathon races result in different ways of metabolic adaption.
References Ahlborg, G., Felig, P., Hagenfeldt, L., Hendler, R., Wahren, J.: Substrate turnover during prolonged exercise in man. J. Clin. Invest. 53, 1080--1090 (1974) Berger, M.: Untersuchungen zur Regulation des Glucosestoffwechsels der Skelettmuskulatur In: Habilitationsschrift, pp. 63--91. Universit/it D/isseldorf 1975 Faloona, G. R., Unger, R. H.: Glucagon. In: Methods of hormone radioimmunoassay, pp. 317-327. New York, London: Academic Press 1974 Goldstein, M. S., Mulfick, V., Huddlestun, B., Levine, R.: Action of muscular work on tranfer of sugar across cell barriers: Comparison with the action of insulin. Am. J. Physiol. 173, 212-216 (1953) Hill, A. V.: The maximal work and mechanical efficiencyof human muscles and their most economical speed. Am. J. Physiol. 56, 19 (1922) Hohorst, H. J.: L-(+)-Lactat-Bestimmung mit Lactat Dehydrogenase und NAD. In: Methoden der enzymatischen Analyse, Bd. II (H. U. Bergmeyer, ed.), pp. 1425-1429. Weinheim: Verlag Chemic 1970 Hollmann, W., Hettinger, Th.: Ausdauer. In: Sportmedizin, Arbeits- und Tralningsgrundlagen (W. Hollmann, ed.), pp. 301-346. Stuttgart, New York: Schattauer 1975 Holloszy, J. O., Bnoth, W., Winder, W, Fitts, R. H.: Biochemical adaptions in muscle. Effects of exercise on mitochondrial oxygen uptake and respiratory enzyme activity in skeletal muscle. J. Biol. Chem. 242, 2278--2282 (1967) Randle, P. J., Garland, P. B., Hales, C. N., Newsholme, E. A.: The glucose fatty acid cycle. Its role in insulin sensitivity and metabolic disturbance of diabetes mellitus. Lancet 1963 I, 785-789 Randle, P. J.: Blood glucose homeostasis - glucose utilization. Nobel Symposia 13, 173-197 (1970)
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Rudermann, N. B., Toews, C. J., Shafrir, E.: Role of free fatty acids in glucose homeostasis. Arch. Intern. Med. 123, 299-313 (1969) Rudermann, N. E.: Muscle amino acid metabolism and gluconeogenesis. Ann~ Rev. Med. 26, 245-258 (1975) Senger, H., Donath, R.: Zur Regulation der oxydativen Substratverwertung im Muskel bei erh/Shtem ATP-Umsatz. Med. Sport 17, 391--401 (1977) Starr, J. I., Rubenstein, A. X.: Insulin, proinsulin and c-peptide. In: Methods of hormone radioimmunoassay. (B. M. Jaffe, H. R. Behrmann, eds.), pp. 289-311. New York, London: Academic Press 1974 Vecsei, P.: Glucocortieoids: Cortisol, Corticosterone, and Compounds. In: Methods of hormone radioimrnunoassay (P. Vecsei, ed.), pp. 393-412. New York, London: Academic Press 1974 Weicker, H., Wirth, A., Spiel, M.: Influence of motoric activation on metabolic regulation and physical efficiency with diabetes mellitus. Inn. Med. 3, 423-429 (1976) Wirth, A., Eckhard, J., Weieker, H.: Automatic potentiometric titration and gas-liquid chromatography of underivated free fatty acids. Clin. Chim. Acta 71, 47-54 (1976) Young, D. R., PeUigra, R., Shapira, J., Adachi, R. R., Skrettingland, K.: Glucose oxidation and replacement during prolonged exercise in man. J. Appl. Physiol. 23, 734-741 (1967) Accepted December 15, 1978
Applied
Eur. J. Appl. Physiol. 41, 101-108 (1979)
Physiology
and Occupational Physiology 9 Springer-Verlag 1979
Metabolic Adaptation to Prolonged Exercise K. Scheele, W. Herzog, G. Ritthaler, A. Wirth, and H. Weicker Institute of Pathophysiology and Sports Medicine University of Heidelberg, D-6900 Heidelberg, Federal Republic of Germany and Institute of Sports Medicine, D-7000 Stuttgart, Federal Republic of Germany
Summary. A study was undertaken to evaluate and to examine the role of substrate supply in 50 healthy subjects after long distance events, such as 10 km, 25 km, and marathon races. The metabolic, variables of carbohydrate metabolism were greatest in 10-km runners, with the highest increase in glucose, lactate, and pyruvate, while in marathon runners only moderate changes were observed. Marathon competitors gave the greatest decrease in insulin concentration whereas glucagon and cortisol showed a contrary tendency. As for lipid concentrations, the most remarkable point was that after the marathon competition the best runners had the highest increase in free fatty acids; the longer the race, the higher were the/3-hydroxybutyrate and acetoacetate levels after the competition. It is important to emphasize that the limiting factor up to 90 min duration is the competitor's ability to deplete the stores of glycogen. Beyond 90 rain (or 25 kin) the decrease in insulin, the rise in cortisol and the higher concentration of ketnne bodies found indicate a change in metabnlic response. Key words: Prolonged exercise - Hormones - Lipolysis metabolism
Carbohydrate
Since 1922 maximal oxygen consumption has been considered as the main fimiting factor of physical capacity (Hill, 1922). In spite of the development of detailed and more definite methods of examining an athlete or a patient, the rate of maximal oxygen consumption has maintained its central position. Spiroergometric resarch and tests on bycycles and treadmills determine the capacity of individual endurance. The most important limiting factors in analysing oxygen consumption and oxygen absorption capacity are perfusion of the respiratory system, cardiac output, blood volume, and total hemoglobin (Hollmann, 1975). On the other hand it is now well Offprint requests to: PD Dr. K. Scheele, Taubenheimstr. 8, D-7000 Stuttgart 50, Federal Republic of Germany
0301-5548/79/0041/0101/$ 01.60
102
K. Scheele et al:
documented that the oxidative capacity in skeletal muscle limits both the intensity and duration o f work (Holloszy, 167). Recent studies have demonstrated that the level of phosphates and glycolytic c a p a c i t y play an important role in the substrate supply o f exercising skeletal muscles during short-term exercise. Skeletal muscle is regarded as a large depot of substrates as well as a place of high utilization of substrates during prolonged physical exercise (Wahren, 1971). U p to 3 min of performance, the energy of muscle contractions is obtained mainly from creatine-phosphate, b y anaerobic depletion of glucose and glycogen, and b y the disposal of adenosine-triphosphate. During this short period, elasticity and frequency of muscle contractions are the limiting factors in physical performance. During long-term exercise aerobic c a p a c i t y becomes important and is determined mainly b y the substrate supply of glucose, free fatty acids, amino acids, and the capacity of enzymes o f the respiratory chain (Holloszy, 1967; Ahlborg, 1974; Hollmann, 1975; Weicker, 176). This study was undertaken to evaluate and to examine the role of substrate supply after extensive prolonged exercise, during long distance events such as 10 km, 25 km, and m a r a t h o n races.
Subjects and Methods
Subjects The metabolic parameters before and after prolonged exercise were examined in 50 healthy subjects. The subjects were classified into groups of 22 subjects over 10 km (17 men, aged 33-49, 5 women, aged 34-56), 11 subjects over 25 km (10 men, aged 32-57, 1 women, aged 41) and 17 marathon runners (14 men, aged 30-63, 3 women, aged 30-63). None of these athletes had a history or evidence of liver disease or other metabolic disorder. Data concerning age, height, and weight were recorded before the competition (average weight of men 73.2 kg, of women 59.8 kg, average height of men 173.5 cm, of women 166,4 cm). All subjects had participated only in occasional training programs beforehand. The 50 subjects may be regarded as moderately trained subjects (ca. 30 min gymnastics per week on average). They were informed of the nature, purpose, and possible risks involved in the study before agreeing to participate.
Methods All athletes were examined 30 min before the competition. Blood samples were obtained by inserting a short catheter into the anticubital vein. This procedure was repeated directly after the end of the competition. Total blood loss during these two procedures was less than 50 ml.
Analysis Blood glucose was determined enzymatically (oxidase -- peroxidase method) with a Beckmann glucose analyzer, lactate and pyruvate (whole blood) by biochemical analysis, and the remaining blood was centrifuged, and aliquots stored at - 2 0 ~ C for further usage. The concentrations of insulin, glucagon, and eorfisol were determined by radio-immunoassay (RIA), insulin after Starr and Rubenstein (1974),
Metabolic Adaptation to Prolonged Exercise
103
using Boehringer Monotest-Insulin, glucagon according to Faloona and Unger (1974) using the kit of toe Novo Research Institute, Bagsvaerd, Denmark, cortisol according to the method of Vecsei (1974), Heidelberg, Pharmakol. Inst. Glycerol and triglycerides were also determined enzymatically, whereas the concentration of free fatty acids was analyzed by titrimetric determination (Wirth et al., 1976). Aceto-acetate and /3-hydroxybutyrate were analyzed by enzymatic fluorimetric micromethods, the determination of urea and creatinine being also analyzed enzymaticallyby a biochemicaltest combination (Boehringer, Mannheim).
Calculation Data in the text, tables, and figures are given as means • SD. Standard statistical methods had been employed, using the paired t-test.
Results Table 1 shows the pre- and post-competition values of glucose, lactate, and pyruvate according to the distance performed. The 10-km athletes increased their contration of glucose by 42.8 mmol/1., the 25-km runners increased by 24.6 mmol/1., and after the m a r a t h o n competition there was no increase at all. Analyzing these results in detail showed that the 3 best athletes had the highest glucose and lactate concentrations after performance. These athletes with the supraphysiological glucose values and highest lactate concentrations did not differ in any other way from the rest of the group. Table 2 shows the concentration of hormones (insulin, glucagon, cortisol). A decrease in insulin concentration of 38. 8 pmol/1 for the 10-km runners, of 36.7 pmol/1 for the 25-km runners, and of 70.1 pmol/1 for the m a r a t h o n runners was observed. The glucagon and cortisol concentrations showed a contrary tendency: the longer the distance, the higher the glucagon and cortisol values (insulin antagonistic hormones).
Table 1. The concentration of blood glucose, lactate, and pyruvate according to performed distance Before
After
Difference
P values
Glucose (mmol/1) 10 km 25 km Marathon
4.81 + 1.02 4.48 _+0.99 5.38 + 1.09
6.87 + 3.51 5.58 + 0.81 5.40 • 1.19
+ 42.8 + 24.6 + 0.4
< 0.01 < 0.01 n.s.
Lactate (mmo~l) 10 km 25 km Marathon
1.59 • 0.67 1.45 _+0.40 1.70 + 0.59
4.31 + 1.34 3.33 + 1.27 2.69 • 0.77
+ 171.1 + 125.0 + 58.2
< 0.001 < 0.001 < 0.001
Pyruvate (mmol/1) 10 km 25 km Marathon
0.063 _+0.025 0.074 + 0.020 0.067 + 0.028
0.192 + 0.077 0.184 + 0.060 0.166 _+0.057
+ 204.8 + 148.6 + 147.8
< 0.001 < 0.001 < 0.001
104
K. Scheele et al.
Table 2. The changes of blood hormone concentration with regard to performed distance Before
After
Difference
P values
Insulin (pmol/1) 10 km 25 km Marathon
116.7 + 106.3 123.0 + 92.1 263.0 + 217.5
71.4 + 68.3 77.8 _+ 45.2 78.6 • 43.7
- 38.8 - 36.7 - 70.1
< 0.05 n.s. < 0.001
Glucagon (pmol/1) 10 km 25 km Marathon
10.62 _+ 7.17 18.36 + 15.49 30.99 + 12.34
13.20 + 8.32 28.12 + 14.92 78.62 _+ 34.15
+ 24.3 + 53.2 + 153.0
n.s. n.s. < 0.001
Cortisol (pmol/1) 10 km 25km Marathnn
0.276 + 0.120 0.261+0.122 0.316 + 0.145
0.407 + 0.156 0.435+0.160 0.553 + 0.274
+ 47.5 +60.5 + 75.0
< 0.001 < 0.001 < 0.001
Table 3. The changes of lipid values with regard to the distance of running Before
After
Difference
P values
Triglycerides (mmol/1) 10 km 1.181 + 0.649 25 km 1.093 + 0.465 Marathon 1.432 + 0.614
0.791 _+0.434 0.678 _+ 0.501 0.689 _+ 0.646
-- 33.0 - 38.0 51.9
n.s.
Glycerol (mmol/1) 10 km 25 km Marathon
0.554 + 0.273 0.914 + 0.343 0.962 + 0.513
+ 166.4 + 345.9 + 403.7
< 0.001 < 0.001 < 0.001
954.4 _+ 393.6 1354.5 + 480.2 1805.5 + 491.6
+ 118.9 + 193.3 + 291.1
< 0.001 < 0.001 < 0.001
0.208 + 0.118 0.205 + 0.120 0.191 _+ 0.111
Free fatty acids (~val/1) 10 km 436.1 + 130.0 25 km 461.8 + 151.7 Marathon 461.6 + 167.3
-
n.s.
< 0.001
T h e c h a n g e s o f lipid values w i t h r e g a r d t o t h e d i s t a n c e c o v e r e d are s h o w n in T a b l e 3. All r u n n e r s s h o w e d a d e c r e a s e in t r i g l y c e r i d e c o n c e n t r a t i o n a f t e r t h e c o m petition, 33.0 m m o l / 1 for t h e 1 0 - k m r u n n e r s , 38.0 m m o l / 1 f o r t h e 2 5 - k i n r u n n e r s , a n d 51.9 m m o l / 1 f o r t h e m a r a t h o n r u n n e r s . T h e g l y c e r o l c o n c e n t r a t i o n s h o w e d a n inc r e a s e o f 166.4 m m o l / l for t h e 1 0 - k i n r u n n e r s , a n i n c r e a s e o f 3 4 5 . 9 m m o l / 1 for t h e 2 5 - k m r u n n e r s , a n d o f 4 0 3 . 7 m m o l / 1 for t h e m a r a t h o n r u n n e r s . A f t e r p e r f o r m a n c e , t h e 1 0 - k m a t h l e t e s s h o w e d a n i n c r e a s e o f 118.9 Cmol/1 in t h e free f a t t y acids, t h e 2 5 - k m r u n n e r s o f 193.3, a n d t h e m a r a t h o n r u n n e r s a n i n c r e a s e o f 291.1 ~mol/1. The concentrations of hydroxybutyrate and acetoacetate rose during exercise a n d t h e r e w a s a t e n d e n c y for t h e levels t o rise m o r e w i t h i n c r e a s e in d i s t a n c e (see T a b l e 4).
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105
Table 4. The blood concentration of/3-hydroxybutyrate and acetoacetate according to the distance covered Before
After
Difference
P values
0.180 + 0.054 0.225 + 0.099 0.236 _+0.100
0.511 _+0.231 0.789 + 0.371 0.867 +_0.479
+ 183.9 + 250.7 + 367.4
< 0.001 < 0.001 < 0.001
Acetoacetate (mmol/1) 10 km 0.013 + 0.013 25 km 0.015 _+0.020 Marathon 0.008 + 0.009
0.040 _+0.026 0.071 + 0.034 0.073 + 0.039
+ 207.7 + 373.3 + 312.5
< 0.001 < 0.001 < 0.001
Hydroxybutyrate (mmol/1) 10 km 25 km Marathon
Table 5. The changes of blood urea and creatinine values according to distance covered Before
After
Difference
P values
Creatinine (~mol/1) 10 km 25 km Marathon
80.5 _+ 11.5 78.7 + 10.6 75.1 + 15.0
76.0 _+ 14.1 101.7 _+ 19.5 121.1 _+21.2
- 5.6 + 29.2 + 61.3
n.s. < 0.001 < 0.001
Urea (mmol/1) 10 km 25 km Marathon
7.03 _+ 1.38 6.89 + 1.41 6.73 _+ 1.49
7.09 _+ 1.35 7.59 + 1.46 9.09 _+ 1.53
+ 1.0 + 10.2 + 35.1
n.s. n.s. < 0.001
The different concentrations of urea and creatinine according to running distance can be seen in Table 5: (a) Creatinine: The 10-km runners show a decrease of 5.6, the 25-km runners an increase of 29.2, and the m a r a t h o n runners an increase of 61.3 ~mol/1. (b) Urea: After the competition, no changes could be discovered for the 10-km runners, where as the 25-km runners showed an increase of 35.1 ~mol/1.
Discussion The results of these investigations show the interdependency of the concentration a n d / o r absorption capacity of the different substrates and the physical capacity of the subjects tested under various conditions (long-distance running over 10 km, 25 km, and marathon). In detail we have to scrutinize the different metabolic ways and parameters influencing and limiting the oxidative capacity of the exercising muscle during and after prolonged sporting activity. I n agreement with findings from previous studies we found that the glucose concentration rises after prolonged exercise (Randle, 1963; R u d e r m a n n , 1969; Sen-
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ger, 1977; see Table 1). There are two remarkable points in these results: The longer the running distance, the lower the increase in glucose. The best runners of the 10km group had the highest glucose and lactate concentration as well as the highest insulin level. It is also noteworthy that after-performance values reach supraphysiological values. Thus our findings support the hypothesis that the aerobic and oxidative requirement of a 60 rain sporting activity such as a 10-km run is a suitable way of depleting the stores of glycogen in exercising muscle and in the liver. As the glycogen stores are depleted by prolonged exercise, the concentration of insulin decreases (Table 2): the longer the exercise, the lower the insulin concentration after performance. In this context it is of interest to note the hypothesis that gluconeogenesis by amino acids has become an important factor (Young, 1967; Rudermann, 1975). On the other hand the possibility of direct oxidation and utilization of lipids is also present (Senger, 1977). In theory, the connection between carbohydrate and lipid metabolism during and after prolonged exercise depends on three circumstances: (1) Intensity, type, and duration of muscular exercise. (2) Nutrition of the athlete. (3) Metabolic adaption. As to the first point, we can see a close connection between glucose concentration and type of performance. After having finished the 10-kin distance, the runners showed an increase in lactate and pyruvate, and the limiting factor of performance is the lactogen - oxygen efficiency, whereas during a run over the marathon distance triglycerides, free fatty acids, and the metabolic response in form of ketone bodies plays a limiting role. The increased oxidation of free fatty acids and the utilization of triglycerides during and after the marathon - seen in the results of the 25-km and marathon runners - includes a block in glucose uptake and utilization by the peripheral muscle. This hypothesis was put forward by Randle (1970). These data show a constant rise in free fatty acids and ketone bodies for the 25-km and even more for the marathon runners; so the most important conclusion of these results is the shift in metabolism from glycogen to lipid oxidation after covering a distance of 25 km. With respect to the decrease in insulin concentration by prolonged exercise it is of interest to note that there is a parallel progressive increase in glucagon and cortisol (Table 4). A decrease in insulin concentration during prolonged exercise has been reported, and is wellknown (Berger, 1975). But there are only few investigations with regard to the period of performance. Our results show the changes in metabolic and hormonal adaptions in a typical way: the longer the distance and time of performance, the higher the concentration of glueagon and cortisol (insulin antagonistic hormones, see Table 2). The increase in glucagon seen in the present study is comparable to the metabolic changes during starvation (Ahlborg et al., 1974). On the other hand, we can assume that there are two effects of the stimulatory influence of glucagon and cortisol: (1) A higher output of hormones stimulating lipolysis, thereby making available to the liver increased quantities of glycerol and free fatty acids. (2) The stimulatory influence of glucose precursors and gluconeogenesis which has been demonstrated elsewhere (Ahlborg et al., 1974). According to Ahlborg (1974) and Senger (1977), an increased hypoxia of muscle tissue is responsible for the insulin clearance during prolonged exercise such as a
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25-km run and marathon. In addition, we can discuss a factor similar to insulin which is produced in prolonged-exercise muscle tissue and causes the increased utilization of glucose in working muscle (Goldstein, 1953, Dieterle, 1973). By means of these data and results we can fairly assume that performed endurance exercise such as long-distance running results in an economic working of metabolism, i.e., a rise in lipolytic capacity, a higher peripheral utilization of glucose, and an increased uptake of glucose precursors causing an acceleration of gluconeogenetic processes (Wahren, 1971). Variation in the individual characteristics of the runners, including the time of the last meal, and differences in the intake of carbohydrates, amino acids, fats, and minerals m a y well be responsible for the large range of values observed before the competition. As to changes in creatinine and urea levels (Table 5) we suggest that these m a y be caused by the muscle cell: the longer the performed exercise, the higher the concentration of creatinine. Thus the highest creatinine concentration occurred after the marathon competition. In the same way we assume that the higher concentration of urea after the marathon competition reflects the restoration of glycogen stores by gluconeogenetic processes. These findings suggest that we should observe the values of branched-chain amino acids in blood samples, and would expect to find the highest values in the best marathon runners. These data will be published later. The results clearly show that the performance of long distance events such as 10 km, 25 km, and marathon races result in different ways of metabolic adaption.
References Ahlborg, G., Felig, P., Hagenfeldt, L., Hendler, R., Wahren, J.: Substrate turnover during prolonged exercise in man. J. Clin. Invest. 53, 1080--1090 (1974) Berger, M.: Untersuchungen zur Regulation des Glucosestoffwechsels der Skelettmuskulatur In: Habilitationsschrift, pp. 63--91. Universit/it D/isseldorf 1975 Faloona, G. R., Unger, R. H.: Glucagon. In: Methods of hormone radioimmunoassay, pp. 317-327. New York, London: Academic Press 1974 Goldstein, M. S., Mulfick, V., Huddlestun, B., Levine, R.: Action of muscular work on tranfer of sugar across cell barriers: Comparison with the action of insulin. Am. J. Physiol. 173, 212-216 (1953) Hill, A. V.: The maximal work and mechanical efficiencyof human muscles and their most economical speed. Am. J. Physiol. 56, 19 (1922) Hohorst, H. J.: L-(+)-Lactat-Bestimmung mit Lactat Dehydrogenase und NAD. In: Methoden der enzymatischen Analyse, Bd. II (H. U. Bergmeyer, ed.), pp. 1425-1429. Weinheim: Verlag Chemic 1970 Hollmann, W., Hettinger, Th.: Ausdauer. In: Sportmedizin, Arbeits- und Tralningsgrundlagen (W. Hollmann, ed.), pp. 301-346. Stuttgart, New York: Schattauer 1975 Holloszy, J. O., Bnoth, W., Winder, W, Fitts, R. H.: Biochemical adaptions in muscle. Effects of exercise on mitochondrial oxygen uptake and respiratory enzyme activity in skeletal muscle. J. Biol. Chem. 242, 2278--2282 (1967) Randle, P. J., Garland, P. B., Hales, C. N., Newsholme, E. A.: The glucose fatty acid cycle. Its role in insulin sensitivity and metabolic disturbance of diabetes mellitus. Lancet 1963 I, 785-789 Randle, P. J.: Blood glucose homeostasis - glucose utilization. Nobel Symposia 13, 173-197 (1970)
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Rudermann, N. B., Toews, C. J., Shafrir, E.: Role of free fatty acids in glucose homeostasis. Arch. Intern. Med. 123, 299-313 (1969) Rudermann, N. E.: Muscle amino acid metabolism and gluconeogenesis. Ann~ Rev. Med. 26, 245-258 (1975) Senger, H., Donath, R.: Zur Regulation der oxydativen Substratverwertung im Muskel bei erh/Shtem ATP-Umsatz. Med. Sport 17, 391--401 (1977) Starr, J. I., Rubenstein, A. X.: Insulin, proinsulin and c-peptide. In: Methods of hormone radioimmunoassay. (B. M. Jaffe, H. R. Behrmann, eds.), pp. 289-311. New York, London: Academic Press 1974 Vecsei, P.: Glucocortieoids: Cortisol, Corticosterone, and Compounds. In: Methods of hormone radioimrnunoassay (P. Vecsei, ed.), pp. 393-412. New York, London: Academic Press 1974 Weicker, H., Wirth, A., Spiel, M.: Influence of motoric activation on metabolic regulation and physical efficiency with diabetes mellitus. Inn. Med. 3, 423-429 (1976) Wirth, A., Eckhard, J., Weieker, H.: Automatic potentiometric titration and gas-liquid chromatography of underivated free fatty acids. Clin. Chim. Acta 71, 47-54 (1976) Young, D. R., PeUigra, R., Shapira, J., Adachi, R. R., Skrettingland, K.: Glucose oxidation and replacement during prolonged exercise in man. J. Appl. Physiol. 23, 734-741 (1967) Accepted December 15, 1978
