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Gastrocnemius muscle from treadmill trained rats was analyzed for creatine kinase (CK) isoenzyme activities by agarose electrophoresis and M and B CK mRNA levels by Northern blot analysis. Total CK activity in exercise-trained (143 (SD 15) U/g) and control (154 (SD 16) U/g) muscles did not differ. CK-MB increased 220% in exercised-trained muscle compared to controls. CK-B subunit mRNA increased 40%, while CK-M subunit mRNA decreased 42% in exercised-trained muscle compared to control. Thus, gene expression of CK isoenzymes appears to be partially controlled at the level of transcription following exercise training.

The time course of changes in serum proteins and other blood constituents after eccentric exercise of the forearm flexors by six nonweight-trained female subjects (age, 19.7 +/- 1.9 years) was investigated. Eccentric muscle actions are those in which the muscle lengthens as it exerts force, as when a person lowers a weight. Serum levels of creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase, myoglobin, as well as urea nitrogen, uric acid, creatinine, calcium, and phosphorus were examined before and for 6 days after exercise. Creatine kinase increased dramatically (peak value ranged from 6740 to 24,200 U/L) and aspartate aminotransferase, lactate dehydrogenase, alanine aminotransferase, and myoglobin followed the same time course as creatine kinase, but their peak values were lower. These proteins did not increase significantly until 48 hours after exercise and reached peak values 3 to 5 days after exercise. Alkaline phosphatase, gamma-glutamyl transpeptidase, uric acid, urea nitrogen, creatinine, calcium, and phosphorus showed no change. There is either a delay in muscle protein release by damaged muscle fibers, or the proteins are unable to leave the interstitial area for the 24 to 48 hour period after exercise. Because of the long delay, care should be taken when blood protein levels are interpreted in persons who have exercised strenuously (even if only for a short period of intense effort) several days before any diagnostic tests are performed.

The geographic distribution of the following enzyme systems is described in the rat heart (left and right ventricles) and in different skeletal muscles (soleus, plantaris, and red and white gastrocnemius): xanthine oxidase and dehydrogenase, creatine kinase isoenzymes, lactate dehydrogenase isoenzymes, and the free radical scavenger enzymes superoxide dismutase, glutathione reductase, and glutathione peroxidase. No substantial difference in enzyme activities was observed between the left and right ventricles. Skeletal muscles showed a clear distinction between enzyme activities depending on their composition of oxidative fibers and glycolytic fibers.

Skeletal muscle damage size (SMDS) was assessed in 35 women and 34 men runners after a 42.2-km race using a method developed for estimation of myocardial infarct size. SMDS was computed according to the following equation: SMDS = (BW) (K) (CKr), where BW is body weight, K is a constant, and CKr is the cumulative amount of creatine kinase (CK) released over time. The method takes into account CK distribution space, fractional disappearance rate of CK, proportion of CK degraded in skeletal muscle, and proportion of CK released into the circulation. Assumptions are made regarding the relative amount of CK lost from skeletal muscle into the circulation. The SMDS in men, 808 +/- 1,229 (SD) CK g-eq was significantly (P less than 0.05) greater than in women, 160 +/- 147 (SD) CK g-eq. The ranges of SMDS (CK g-eq) were 23-5,397 in men and 7-624 in women. A significant difference (P less than 0.05) also remained after correction for body surface area; men 432 +/- 583 (SD), women 100 +/- 63 (SD) CK g-eq/m2. In men and women, no significant correlation existed between SMDS and age or marathon finish time. Although relatively theoretical, results indicate that greater skeletal muscle damage occurred in men vs. women runners after a marathon. Whether the release of CK from skeletal muscle is the result of irreversible and/or reversible injury has not yet been determined.

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.

Individual human muscle fibers from the vastus lateralis were isolated from age-matched endurance-trained and strength-trained athletes and untrained controls. Slow- (ST) and fast-twitch (FT) fibers were assayed for total creatine kinase (CK), CK-MB, total lactate dehydrogenase (LD), the LD isozyme that predominates in the heart muscle of most vertebrates (LD1), and citrate synthase (CS). Regardless of training of the athletes, both CK-MB and CS were higher in ST than in FT fibers. Also, irrespective of fiber type, CK-MB and CS were greatest in the endurance-trained group. A positive correlation existed between CK-MB and CS, relating oxidative capacity of individual fibers with CK-MB. Total CK varied little among the fiber types, trained groups, or controls. Total LD in FT fibers was greater than in ST fibers in all groups, with only ST fibers from the endurance-trained group containing substantial amounts of LD1. These findings suggest that specific training, endurance exercise, causes a favorable metabolic adaptation of CK and LD isozymes at the individual fiber level, allowing for the muscle to cope with increased energy demands during prolonged exercise.

We investigated the patterns of variants of creatine kinase isoenzyme MM (CK-MM) in gastrocnemius muscle and plasma sampled from male and female long-distance runners before and after a marathon race. The proportions of CK-MM variants MM1 (pI 6.90) and MM2 (pI 6.62), identified in the skeletal muscle from both sexes, did not differ significantly from those in skeletal muscle from nonrunning controls or from heart muscle. CK-MM1 was the major (84-85% of total CK-MM) variant form. Patterns of CK-MM in plasma collected from male runners 24, 48, 72, and 96 h after the race were similar to those for female runners, but we detected two new additional variants, which we designate MM1B (pI 6.76) and MM2B (pI 6.49). For both sexes the total CK-MM activities in plasma were significantly (p less than 0.05) greater after the race, but the women's total CK-MM activities were significantly (p less than 0.05) less than the men's. The rates of disappearance of MM1, MM2, and MM3 from plasma after the race differed significantly (p less than 0.05) between men and women, MM1 clearing the fastest. Determination of the CK-MM variants in plasma after strenuous exercise may be of help in assessing CK release from injured skeletal muscle.

The proportion of creatine kinase (CK; EC 2.7.3.2) isoenzyme MB activity was increased in skeletal muscle biopsies obtained from five long-distance runners, both 2 h before (mean 7.7%, SD 2.4%) and 30 min after (mean 7.2%, SD 1.2%) a marathon race, as compared with that in biopsies from five nonrunners (controls less than or equal to 1.0%). Further, mitochondrial CK and CK-BB isoenzymes were present in homogenates of the runners' skeletal muscle samples but not in those of the nonrunners. However, there were no substantial differences in the mean total CK activities per gram (wet wt.) of muscle tissue among premarathon samples, postmarathon samples, and nonrunners' samples (3148, 3365, and 3049 U/g, respectively). We conclude that the metabolically active gastrocnemius muscle of long-distance runners is qualitatively similar to the heart muscle in its CK isoenzyme composition.

We could detect skeletal muscle injury early after an acute exercise bout by measuring creatine kinase (CK, EC 2.7.3.2) MM isoforms in serum. Eleven men performed 120 alternating-arm, eccentric (muscle lengthening) biceps contractions with the intensity of each contraction being 110% of maximal concentric strength--a form of exercise previously shown to cause significant increases of CK in serum at 24 h and muscle soreness 48 h after exercise. Total CK and CK-MM isoform activities in serum were determined before and at 0.5, 0.75, 1, 1.5, 2, and 6 h after exercise. Using thin-film agarose gels and a rapid isoelectric focusing technique, we separated the MM isoforms into MM3 (skeletal muscle form), MM2, and MM1 (in vivo conversion forms). The isoforms reflected the MM form released into the serum from tissue as well as the conversion of one form to another. There were no significant increases in total CK from before to 6 h after exercise: 75 (SD 36) vs 91 (SD 33) U/L. However, CK MM3 in serum increased significantly (P less than 0.01) within 2 h after exercise from 22 (SD 6)% to 28 (SD 6)%. The MM3 to MM1 ratio also increased significantly (P less than 0.05) during this time, from 0.6 (SD 0.3) to 0.9 (SD 0.4). Thus, quantification of CK MM isoforms permitted very early detection of skeletal muscle enzyme release.

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.

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.

Serum samples from 14 men and 8 women were obtained pre-marathon (48 h) and at 24, 48, 72, and 96 h post-race to quantitate total serum creatine kinase activity (TCK), percentage of creatine kinase MB (CK-MB), and clearance rates (half-lives) of TCK and CK-MB. TCK was measured enzymatically, and the CK-MB isoenzyme was separated by agarose electrophoresis and quantitated by densitometry. The men's and women's post-race mean TCK levels were significantly elevated (P less than 0.05) above pre-race values at 24 h (3322 U . l-1, 946 U . l-1 and 48 h (1787 U . l-1, 508 U . l-1). In addition, CK-MB was significantly elevated both 24 h (5.1%, 3.3%) and 48 h (2.5%, 1.8%) post-race (P less than 0.05). The men's 24-h TCK was 22.3 times the pre-race value, while the women had an 8.6-fold increase in TCK. The mean 24-h post-race CK-MB activities were 166 U . l-1 for the men and 31 U . l-1 for the women. The mean increase in CK-MB activity was 41.5-fold for the men and 7.8-fold for the women. Furthermore, the men had a mean half-life (t1/2) of 30.4 h for TCK and 12.0 h for CK-MB; the women's t1/2's were 29.4 and 16.8 h, respectively. At all time points, the men evidenced significantly (P less than 0.05) higher TCK and CK-MB enzyme activities than did the women.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to investigate the kinetic properties of human creatine kinase (CK) isoenzymes partially purified from heart and skeletal muscle. Utilizing the backward CK-catalyzed reaction of creatine phosphate + ADP in equilibrium creatine + ATP, Km values for heart and skeletal muscle CK MM (3.7 mmol/l) were significantly (p less than 0.05) greater than CK MB (2.1 mmol/l) which were significantly (p less than 0.05) greater than mitochondrial CK (1.8 mmol/l) at variable creatine phosphate and fixed ADP concentrations. However, Km values for similar isoenzymes from the two different tissues, i.e., CK MB from heart vs. skeletal muscle, were not different. These results show that kinetic analysis of CK isoenzymes cannot differentiate the tissue source of elevated blood CK isoenzymes after the acute stress of long distance running or after acute myocardial infarction.

The present study assessed creatine kinase (CK) activity, CK MM isoforms, and muscle soreness following an exercise regimen designed to induce skeletal muscle damage. Eight college-age subjects performed 40 maximal isometric contractions of the knee extensor muscles (10-second contraction/20-second rest). Serum samples and soreness ratings were taken prior to and 2, 6, 18, and 24 hours after the exercise. The CK MM1 and CK MM3 isoforms were determined by flatbed isoelectric focusing (IEF). In serum, the MM1 isoform (the pure gene product) is considered to be evidence of newly released CK from muscle, as upon entering the plasma, the CK MM1 is converted to MM2 and then MM3. A significant increase in serum CK activity was found at 6 hours and remained elevated at 24 hours. CK MM1 increased significantly at 2 hours, peaked at 6 hours, then approached baseline. Soreness did not increase significantly until 18 hours. Analysis of CK isoforms in serum can provide an earlier indicator of skeletal muscle damage than total CK or perception of soreness and may be useful in tracking the time course of skeletal muscle damage and repair.