CK-MM and ACE genotypes and physiological prediction of the creatine kinase response to exercise

Exertional rhabdomyolysis: a clinical review with a focus on genetic influences

In this review, the clinical and laboratory features of exertional rhabdomyolysis (ER) are discussed in detail, emphasizing the full clinical spectrum from physiological elevations of serum creatine kinase after exertion to life-threatening rhabdomyolysis with acute kidney injury and associated systemic complications. Laboratory markers used to diagnose both ER and rhabdomyolysis are very sensitive, but not very specific, and imperfectly distinguish "subclinical" or asymptomatic from severe, life-threatening illness. However, genetic factors, both recognized and yet to be discovered, likely influence this diverse clinical spectrum of disease and response to exercise. Genetic mutations causative for McArdle disease, carnitine palmitoyl transferase deficiency 2, myoadenylate deaminase deficiency, and malignant hyperthermia have all been associated with ER. Polymorphic variations in the myosin light chain kinase, α-actin 3, creatine kinase-muscle isoform, angiotensin I-converting enzyme, heat shock protein, and interleukin-6 genes have also been associated with either ER or exercise-induced serum creatine kinase elevations typical of ER. The prognosis for ER is significantly better than that for other etiologies of rhabdomyolysis, but the risk of recurrence after an initial episode is unknown. Guidelines for management are provided.

Creatine kinase activity weakly correlates to volume completed following upper body resistance exercise

In the current study, we examined the relationship between serum creatine kinase (CK) activity following upper body resistance exercise with a 1- or 3-min rest between sets. Twenty men performed two sessions, each consisting of four sets with a 10-repetition maximum load. The results demonstrated significantly greater volume for the 3-min condition (M = 4156 kg, SD = 867, for 3 min; vs. M = 3503 kg SD = 759, for 1 min; p < .001), with no significant differences in delta CK activity between conditions (p = .574). Nevertheless, there was a weak correlation between the delta CK activity and total volume of exercise completed (r = .55 with a 1-min rest, and r = .45 with a 3-min rest). Therefore, the volume following upper body resistance exercise correlates weakly with serum CK levels, irrespective of rest interval length between sets.

Serum creatine kinase after exercise: drawing the line between physiological response and exertional rhabdomyolysis

INTRODUCTION

In this investigation we assessed the spectrum of creatine kinase (CK) responses in military recruits undergoing basic training.

METHODS

Musculoskeletal examination data, questionnaire findings, and CK levels were obtained from 499 recruits at days 0, 3, 7, and 14 of training. Correlations of CK with ethnicity, age, body mass index, exercise, muscle pain, and climate were obtained.

RESULTS

None of the subjects developed clinical exertional rhabdomyolysis (ER). The mean/median serum CK values were 223/157, 734/478, 1226/567, and 667/486 IU/L at days 0, 3, 7, and 14, respectively, with a wide overall range (34-35,056 IU/L). African-American subjects had higher mean CK levels.

CONCLUSIONS

CK elevations and muscle pain are common during basic training. Widely accepted laboratory diagnostic values for ER are routinely exceeded in this military recruits, suggesting that CK levels >50 times the upper limit of normal are more specific. The findings support using CK as a marker for ER. Normal laboratory reference ranges for CK should be published by ethnicity.

Creatine-kinase- and exercise-related muscle damage implications for muscle performance and recovery

The appearance of creatine kinase (CK) in blood has been generally considered to be an indirect marker of muscle damage, particularly for diagnosis of medical conditions such as myocardial infarction, muscular dystrophy, and cerebral diseases. However, there is controversy in the literature concerning its validity in reflecting muscle damage as a consequence of level and intensity of physical exercise. Nonmodifiable factors, for example, ethnicity, age, and gender, can also affect enzyme tissue activity and subsequent CK serum levels. The extent of effect suggests that acceptable upper limits of normal CK levels may need to be reset to recognise the impact of these factors. There is a need for standardisation of protocols and stronger guidelines which would facilitate greater scientific integrity. The purpose of this paper is to examine current evidence and opinion relating to the release of CK from skeletal muscle in response to physical activity and examine if elevated concentrations are a health concern.

Muscle fatigue experienced during maximal eccentric exercise is predictive of the plasma creatine kinase (CK) response

Unaccustomed eccentric exercise may cause skeletal muscle damage with an increase in plasma creatine kinase (CK) activity. Although the wide variability among individuals in CK response to standardized lengthening contractions has been well described, the reasons underlying this phenomenon have not yet been understood. Therefore, this study investigated a possible correlation of the changes in muscle damage indirect markers after an eccentric exercise with the decline in muscle performance during the exercise. Twenty-seven healthy untrained male subjects performed three sets of 30 maximal isokinetic eccentric contractions of the knee extensors. The muscular work was recorded using an isokinetic dynamometer to assess muscle fatigue by means of various fatigue indices. Plasma CK activity, muscle soreness, and stiffness were measured before (pre) and one day after (post) exercise. The eccentric exercise bout induced significant changes of the three muscle damage indirect markers. Large inter-subject variability was observed for all criteria measured. More interestingly, the log (CK(post) /CK(pre)) and muscle stiffness appeared to be closely correlated with the relative work decrease (r = 0.84, r(2)  = 0.70 and r = 0.75, r(2)  = 0.56, respectively). This is the first study to propose that the muscle fatigue profile during maximal eccentric protocol could predict the magnitude of the symptoms associated with muscle damage in humans.

The ACE gene and human performance: 12 years on

Some 12 years ago, a polymorphism of the angiotensin I-converting enzyme (ACE) gene became the first genetic element shown to impact substantially on human physical performance. The renin-angiotensin system (RAS) exists not just as an endocrine regulator, but also within local tissue and cells, where it serves a variety of functions. Functional genetic polymorphic variants have been identified for most components of RAS, of which the best known and studied is a polymorphism of the ACE gene. The ACE insertion/deletion (I/D) polymorphism has been associated with improvements in performance and exercise duration in a variety of populations. The I allele has been consistently demonstrated to be associated with endurance-orientated events, notably, in triathlons. Meanwhile, the D allele is associated with strength- and power-orientated performance, and has been found in significant excess among elite swimmers. Exceptions to these associations do exist, and are discussed. In theory, associations with ACE genotype may be due to functional variants in nearby loci, and/or related genetic polymorphism such as the angiotensin receptor, growth hormone and bradykinin genes. Studies of growth hormone gene variants have not shown significant associations with performance in studies involving both triathletes and military recruits. The angiotensin type-1 receptor has two functional polymorphisms that have not been shown to be associated with performance, although studies of hypoxic ascent have yielded conflicting results. ACE genotype influences bradykinin levels, and a common gene variant in the bradykinin 2 receptor exists. The high kinin activity haplotye has been associated with increased endurance performance at an Olympic level, and similar results of metabolic efficiency have been demonstrated in triathletes. Whilst the ACE genotype is associated with overall performance ability, at a single organ level, the ACE genotype and related polymorphism have significant associations. In cardiac muscle, ACE genotype has associations with left ventricular mass changes in response to stimulus, in both the health and diseased states. The D allele is associated with an exaggerated response to training, and the I allele with the lowest cardiac growth response. In light of the I-allele association with endurance performance, it seems likely that other regulatory mechanisms exist. Similarly in skeletal muscle, the D allele is associated with greater strength gains in response to training, in both healthy individuals and chronic disease states. As in overall performance, those genetic polymorphisms related to the ACE genotype, such as the bradykinin 2 gene, also influence skeletal muscle strength. Finally, the ACE genotype may influence metabolic efficiency, and elite mountaineers have demonstrated an excess of I alleles and I/I genotype frequency in comparison to controls. Interestingly, this was not seen in amateur climbers. Corroboratory evidence exists among high-altitude settlements in both South America and India, where the I allele exists in greater frequency in those who migrated from the lowlands. Unfortunately, if the ACE genotype does influence metabolic efficiency, associations with peak maximal oxygen consumption have yet to be rigorously demonstrated. The ACE genotype is an important but single factor in the determinant of sporting phenotype. Much of the mechanisms underlying this remain unexplored despite 12 years of research.

Creatine kinase MM TaqI and methylenetetrahydrofolate reductase C677T and A1298C gene polymorphisms influence exercise-induced C-reactive protein levels

Physical training induces beneficial adaptations, but exhausting exercise increases reactive oxygen species, which can cause muscular injuries with consequent inflammatory processes, implying jeopardized performance and possibly overtraining. Acute strenuous exercise almost certainly exceeds the benefits of physical activity; it can compromise performance and may contribute to increased future risk of cardiovascular disease (CVD) in athletes. Polymorphisms in the muscle-type creatine kinase (CK-MM) gene may influence performance and adaptation to training, while many potentially significant genetic variants are reported as risk factors for CVD. Therefore, we investigated the influence of polymorphisms in CK-MM TaqI and NcoI, methylenetetrahydrofolate reductase (MTHFR C677T and A1298C) and C-reactive protein (CRP G1059C) genes on exercise-induced damage and inflammation markers. Blood samples were taken immediately after a race (of at least 4 km) that took place outdoors on flat tracks, and were submitted to genotyping and biochemical evaluation of aspartate aminotransferase (AST), CK, CRP and high-sensitivity CRP (hs-CRP). CK-MM TaqI polymorphism significantly influenced results of AST, CK and hs-CRP, and an association between MTHFR C677T and A1298C with CRP level was found, although these levels did not exceed reference values. Results indicate that these polymorphisms can indirectly influence performance, contribute to higher susceptibility to exercise-induced inflammation or protection against it, and perhaps affect future risks of CVD in athletes.

Genetic polymorphisms influence runners' responses to the dietary ingestion of antioxidant supplementation based on pequi oil (Caryocar brasiliense Camb.): a before-after study

Genes have been implicated in the levels of oxidative stress, lipids, CVD risk, immune reactivity, and performance. Pequi oil (Caryocar brasiliense) has shown anti-inflammatory and hypotensive effects, besides reducing exercise-induced DNA, tissue damages, and anisocytosis. Given that diet can interact with the human genome to influence health and disease, and because genetic variability can influence response to diet, we aim to investigate the influence of 12 gene polymorphisms on inflammatory markers, postprandial lipids, arterial pressure, and plasma lipid peroxidation of runners (N = 125), before and after 14 days of 400 mg pequi-oil supplementation, after races under closely comparable conditions. Arterial pressure was checked before races; blood samples were taken immediately after racing to perform leukogram and plateletgram, Tbars assay, lipid, and CRP dosages and genotyping. CAT, GST-M1/T1, CRP-G1059C, and MTHFR-C677T polymorphisms influenced post-pequi-oil responses in leukogram; Hp and MTHFR-C677T, in plateletgram; Hp, ACE, GSTT1, and MTHFR-A1298C, in lipid profile; MTHFR-A1298C, in C-reactive protein (CRP) levels; and Hp and MnSOD, in Tbars assay. Differences between ACE genotypes in leukogram and total cholesterol disappeared after pequi, and the same occurred for Hp and MnSOD in Tbars assay and for MTHFR-A1298C with CRP levels. Because genetic inheritance is one of the factors that drive atherosclerosis-related lipid abnormalities, results can contribute to a greater understanding of the influence of genetic polymorphisms in situations that push up free radicals. Knowledge is also expanded on how antioxidant supplementation affects an individual's genes and how athletic genetic makeup can affect the way a person responds to antioxidant supplements.

Rest Interval Between Resistance Exercise Sets: Length Affects Volume But Not Creatine Kinase Activity or Muscle Soreness

Purpose:

To compare differences between two different rest interval lengths between sets on the volume completed, muscle damage and muscle soreness during a resistance exercise bout.

Methods:

Twenty-eight healthy sedentary men (18 ± 1 y old) volunteered to participate in this study and were divided into the 1 min (1RI; n = 14) or 3 min (3RI; n = 14) rest interval length between sets. They were submitted to maximal voluntary isometric contraction strength (MVC) and then performed a resistance exercise protocol constituted for three sets of biceps curl at 40% of MVC with 1 min (1RI group) or 3 min (3RI group) interval length between sets. Each bout was performed to voluntary fatigue and the workout volume completed was calculated. Subjects provided blood samples before each bout, and at 24, and 48 h following exercise to evaluate serum CK activity. Muscle soreness was analyzed through visual analog scale, which was presented to subjects before frst bout, immediately after exercise protocol and at 24, and 48 h following exercise.

Results:

The results demonstrated that the subjects with longer rest intervals provide greater workout volume as expected, but there were no differences in serum CK activity and muscle soreness between groups.

Conclusion:

Training with highvolume, low-intensity resistance training, exercising with short rest intervals does not appear to present any additional challenge to recovery in untrained subjects.

Short recovery augments magnitude of muscle damage in high responders

PURPOSE

To examine serum creatine kinase (CK) activity after resistance exercise bouts with different rest intervals between sets and exercises in high responding (HR) and normal responding (NR) subjects.

METHODS

During each resistance exercise bout, three sets with 10-repetition maximum (10RM) loads were completed for the chest press, cable pulldown, biceps curl, triceps extension, leg extension, and prone leg curl. Each bout differed in the length of the rest interval between sets and exercises, specifically either 1 or 3 min. After blood analysis, subjects were separated into NR or HR on the basis of the peak serum CK activity being in the 90th percentile.

RESULTS

The volume completed (load x sets x repetitions) was significantly greater for the 3-min bout versus the 1-min bout, with no significant differences between the HR and the NR groups. For the NR group, serum CK was significantly elevated from 24 to 72 h after each bout, with no significant differences between bouts. Conversely, for the HR group, the 1-min bout resulted in serum CK activity levels that were approximately 70% greater than the 3-min bout at the 48- and 72-h time points.

CONCLUSIONS

The key finding from the current study was that the HR group experienced significantly greater CK responses when using shorter rest intervals between sets. Conversely, for the NR group, CK responses were not significantly different between bouts. These findings may have implications for resistance exercise prescription in that some individuals might be less tolerant of shorter rest intervals between sets with greater skeletal muscle microtrauma.

Effects of statins on skeletal muscle: a perspective for physical therapists

Hyperlipidemia, also known as high blood cholesterol, is a cardiovascular health risk that affects more than one third of adults in the United States. Statins are commonly prescribed and successful lipid-lowering medications that reduce the risks associated with cardiovascular disease. The side effects most commonly associated with statin use involve muscle cramping, soreness, fatigue, weakness, and, in rare cases, rapid muscle breakdown that can lead to death. Often, these side effects can become apparent during or after strenuous bouts of exercise. Although the mechanisms by which statins affect muscle performance are not entirely understood, recent research has identified some common causative factors. As musculoskeletal and exercise specialists, physical therapists have a unique opportunity to identify adverse effects related to statin use. The purposes of this perspective article are: (1) to review the metabolism and mechanisms of actions of statins, (2) to discuss the effects of statins on skeletal muscle function, (3) to detail the clinical presentation of statin-induced myopathies, (4) to outline the testing used to diagnose statin-induced myopathies, and (5) to introduce a role for the physical therapist for the screening and detection of suspected statin-induced skeletal muscle myopathy.

Relationship between serum creatine kinase activity following exercise-induced muscle damage and muscle fibre composition

In this study, we examined the relationship between serum creatine kinase activity following exercise-induced muscle damage and muscle fibre composition. Seventeen untrained males volunteered and underwent a .[Vdot]O2max test, Wingate test, and an exercise-induced muscle damage protocol. Muscle soreness and blood samples were recorded before, immediately after, and 24, 48, 72, and 96 h after exercise. Biopsy samples from the vastus lateralis were collected one week after exercise-induced muscle damage and were assessed for muscle fibre composition. There was no significant relationship (P > 0.05) between muscle fibre composition and creatine kinase activity. A significant positive correlation (P < 0.05) was observed between soreness 48 h after exercise and type II and IIb fibres, and a significant negative correlation (P < 0.05) was observed between soreness 48 h after exercise and type I muscle fibres. Significant positive correlations were observed between soreness 48 h after exercise and the fatigue index, relative average power, and relative anaerobic capacity. Our results suggest that creatine kinase activity following exercise-induced muscle damage may not be related to muscle fibre proportions, and higher post-exercise muscular pain may be related to a predominance of type II muscle fibres and higher anaerobic capabilities.

CCL2 and CCR2 polymorphisms are associated with markers of exercise-induced skeletal muscle damage

Novel eccentric (lengthening contraction) exercise typically results in muscle damage, which manifests as prolonged muscle dysfunction, delayed onset muscle soreness, and leakage of muscle proteins into circulation. There is a large degree of variability in the damage response of individuals to eccentric exercise, with higher responders at risk for potentially fatal rhabdomyolysis. We hypothesized that single nucleotide polymorphisms (SNPs) in chemokine ligand 2 ( CCL2) and its receptor chemokine receptor 2 ( CCR2) associate with the high degrees of variability in the muscle damage response. We based this hypothesis on CCL2's roles in macrophage and satellite cell signaling in injured muscle. DNA was obtained from 157 untrained men and women following maximal eccentric exercise. Strength loss, soreness, serum creatine kinase (CK), and myoglobin levels before and during recovery from a single exercise bout were tested for association with 16 SNPs in CCL2 and CCR2. The rare alleles for rs768539 and rs3918358 (CCR2) were significantly ( P < 0.05) associated with lower preexercise strength in men, whereas CCL2 SNPs (rs13900, rs1024611, and rs1860189) and CCR2 (rs1799865) were associated with altered preexercise CK levels in women. During recovery, the rs3917878 genotype ( CCL2) was associated with attenuated strength recovery in men and an elevated CK response in women. CCR2 variants were associated with slower strength recovery in women (rs3918358) and elevated soreness (rs1799865) across all subjects. In summary, we found that SNPs in CCL2 and CCR2 are associated with exercise-induced muscle damage and that the presence of certain variants may result in an exaggerated damage response to strenuous exercise.

Evaluation of gene polymorphisms in exercise-induced oxidative stress and damage

Many potentially significant genetic variants related to oxidative stress have been identified and performance in endurance sports is a multi-factorial phenotype. Thus, it was decided to investigate the influences of the haptoglobin (Hp), MnSOD (Val9Ala), CAT (21A/T), GPX1 (Pro198Leu), ACE, glutathione S-transferases M1 (GSTM1) and T1 (GSTT1) genes' polymorphisms on the oxidative stress and damage suffered by human athletes (runners). Blood samples taken immediately after a race were submitted to genotyping, comet and TBARS assays, biochemical analyses of creatine kinase (CK), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). MnSOD significantly influenced results of CK and a possible association between Hp1F-1S and Hp1S-2 genotypes with a superior TBARS values was found. Higher or lower TBARS and CK values or DNA damage also depended on the interaction between Hp and ACE or GST genotypes, indicating that MnSOD and Hp polymorphisms can be determining factors in performance, at least for runners.

A protocol comparison for the analysis of heat shock protein A1B +A1538G SNP

Heat shock proteins act as molecular chaperones, assist in peptide maturation, and transport nascent peptides across membranes. One commonly studied single nucleotide polymorphism (SNP) for one of the proteins is HSPA1B (+A1538G). However, several studies of this polymorphism have failed to achieve Hardy-Weinberg equilibrium (HWE) for their sample. We compared various published procedures for analyzing the HSPA1B +A1538G SNP and report reasons for HWE discrepancies. Samples from 141 apparently healthy, physically active, volunteers (99 men and 42 women) were analyzed. The first protocol, initially described by Schröder et al., resulted in a genotypic distribution of 22 GG (15.6%), 119 AG (84.4%), and 0 AA; results were confirmed by reanalysis and sequencing. Two other published protocols, one described by Klausz et al. and another by Fekete et al., were used to confirm these results: both resulted in 22 GG (15.6%), 46 AA (32.6%), and 73 AG (51.7%). Additionally, the results were within HWE and confirmed by sequence analysis. Of the original 119 subjects genotyped as AG by the Schröder protocol, 46 of those were confirmed as AA with the Klausz and Fekete methods. Mixing primers from the Schröder and Klausz protocol resulted in 100% concordance with the data generated by the Klausz and Fekete protocols. Some published data on HSP genotyping deviate from HWE; thus, primers used for analyzing these highly homologous genes must be carefully considered. Our results highlight the importance of reinvestigating data when HWE is not achieved for the HSPA1B, or another, polymorphism.

Rhabdomyolysis: a review, with emphasis on the pediatric population

Rhabdomyolysis is a common clinical syndrome and accounts for 7% of all cases of acute kidney injury (AKI) in the USA. It can result from a wide variety of disorders, such as trauma, exercise, medications and infection, but in the pediatric population, infection and inherited disorders are the most common causes of rhabdomyolysis. Approximately half of patients with rhabdomyolysis present with the triad of myalgias, weakness and dark urine. The clinical suspicion, especially in the setting of trauma or drugs, is supported by elevated creatinine kinase levels and confirmed by the measurement of myoglobin levels in serum or urine. Muscle biopsy and genetic testing should be performed if rhabdomyolysis is recurrent or metabolic myopathy is suspected. Early recognition is important to prevent AKI through the use of aggressive hydration. Prevention is important in patients with inherited forms, but novel therapies may be developed with the better understanding of the pathophysiology and genetics of rhabdomyolysis.

Return to physical activity after exertional rhabdomyolysis

Exertional rhabdomyolysis (ER) is a condition characterized by muscle pain, swelling, and weakness following some exertional stress, with or without concomitant heat stress. Athletes who experience ER often present to the emergency department, the training room, or the physician's office seeking guidance and care for this condition, often feeling it is simply normal delayed onset muscle soreness. The astute clinician must perform a thorough history and focused exam, in addition to ordering a serum creatine kinase (CK) and urinalysis. In this clinical setting, a CK equal to or greater than five times normal or a urine dipstick testing positive for blood with no demonstrable red blood cells upon microscopic assessment confirms the diagnosis. A urine or serum myoglobin is more definitive when expeditiously available. After treatment for ER, the provider must risk-stratify the athlete for risk of recurrence, consider further testing, and make the difficult decision on when, if, and under what conditions the athlete can safely return to play.

IL6 (-174) and TNFA (-308) promoter polymorphisms are associated with systemic creatine kinase response to eccentric exercise

Exertional rhabdomyolysis is a complex and poorly understood entity. The inflammatory system has an important role in muscle injury and repair. Serum creatine kinase (CK) is often used as systemic biomarker representing muscle damage. Considerable variation exists in CK response between different subjects. Genetic elements may act as predisposition factors for exertional rhabdomyolysis. Based on their biological activity, we hypothesized that in healthy subjects IL6 G-174C and TNFA G-308A promoter polymorphisms would be associated with CK response to exercise. We determined serum CK activity pre- and post-maximal eccentric contractions of the elbow flexor muscles. IL6 G-174C and TNFA G-308A genotypes were analyzed for possible relationship with changes in serum CK activity. IL6 G-174C genotype was associated with CK activity in a dose-dependent fashion. Subjects with one or more of the -174C allele had a greater increase and higher peak CK values than subjects homozygous for the G allele (mean +/- SE U/L: GG, 2,604 +/- 821; GC, 7,592 +/- 1,111; CC, 8,403 +/- 3,849, ANOVA P = 0.0003 for GG + GC genotypes versus CC genotype, P = 0.0005 for linear trend). IL6-174CC genotype was associated with a greater than threefold increased risk of massive CK response (adjusted odds ratio 3.29, 95% confidence interval 1.27-7.85, P = 0.009). A milder association (P = 0.06) was noted between TNFA G-308A genotype and CK activity. In conclusion, we found a strong association of the IL6 G-174C genotype with systemic CK response to strenuous exercise. Data suggest that homozygosity for the IL6-174C allele is a clinically important risk factor for exercise-induced muscle injury, further supporting the central role of cytokines in the reactive inflammatory process of muscle damage and repair.

ACE ID genotype affects blood creatine kinase response to eccentric exercise

Unaccustomed exercise may cause muscle breakdown with marked increase in serum creatine kinase (CK) activity. The skeletal muscle renin-angiotensin system (RAS) plays an important role in exercise metabolism and tissue injury. A functional insertion (I)/deletion (D) polymorphism in the angiotensin I-converting enzyme (ACE) gene (rs4646994) has been associated with ACE activity. We hypothesized that ACE ID genotype may contribute to the wide variability in individuals' CK response to a given exercise. Young individuals performed maximal eccentric contractions of the elbow flexor muscles. Pre- and postexercise CK activity was determined. ACE genotype was significantly associated with postexercise CK increase and peak CK activity. Individuals harboring one or more of the I allele had a greater increase and higher peak CK values than individuals with the DD genotype. This response was dose-dependent (mean +/- SE U/L: II, 8,882 +/- 2,362; ID, 4,454 +/- 1,105; DD, 2,937 +/- 753, ANOVA, P = 0.02; P = 0.009 for linear trend). Multivariate stepwise regression analysis, which included age, sex, body mass index, and genotype subtypes, revealed that ACE genotype was the most powerful independent determinant of peak CK activity (adjusted odds ratio 1.3, 95% confidence interval 1.03-1.64, P = 0.02). In conclusion, we indicate a positive association of the ACE ID genotype with CK response to strenuous exercise. We suggest that the II genotype imposes increased risk for developing muscle damage, whereas the DD genotype may have protective effects. These findings support the role of local RAS in the regulation of exertional muscle injury.