Left: Note Damaged Muscle Fibers vs. Right: No Damage

How much can exercise raise creatine kinase level —and does it matter?

Journal of Family Practice, August, 2008 by Joshua Latham, Darren Campbell, William Nichols

Moderate-intensity exercise (maintaining heart rate between 55% and 90% of maximum) may elevate creatine kinase (CK) to levels that meet the diagnostic criteria for rhabdomyolysis if the exercises involve eccentric muscle contractions, such as weight lifting or downhill running (strength of recommendation [SOR]: C, small observational studies). The clinical significance of exercise-induced elevations in CK is unclear because the renal complications associated with classic rhabdomyolysis haven’t been observed.

Elevated CK noted on incidental testing can be vexing for physicians who treat athletes. Because asymptomatic exertional rhabdomyolysis is historically underdiagnosed and underappreciated, one may feel compelled to test all such patients for renal function, electrolytes, and myoglobinuria. (1)

Vigilance is mandatory–especially for symptoms of myalgia, generalized weakness, and dark urine–but this Clinical Inquiry also supports using a sound patient history and clinical judgment to avoid extensive laboratory testing or hospital admission. Indeed, patients who participate in moderate intensity, eccentric muscle contraction activities can be followed as outpatients because a correlation between CK elevation and renal dysfunction has not been detected in this group.

Serum creatine kinase as an indicator of local muscular strain in experimental and occupational work

International Archives of Occupational and Environmental Health

Summary Serum creatine kinase (SCK) was measured in ten subjects in the laboratory before and after the performance of bicycle ergometry and a lifting task. SCK was significantly increased 24 h and 48 h after the lifting work but not after the bicycle ergometry, although the work performed on the latter was four-times as great as on the former.


Normal values of CK are difficult to estimate due to individual and population variation in serum levels. Persistent high levels of CK may be seen in blacks compared with other races, males compared with females, and in those with large muscle mass.7,8 In one study of normal adults, reported mean total CK was 147 U/L (range of 7 to 284 U/L) for 57 black males, 61 U/L (range 35 to 87 U/L) for 44 white males, 66 U/L (range 16 to 116 U/L) for 90 black females, and 37 U/L (range 19 to 55 U/L) for 99 white females.7 This study highlighted a lack of specificity when laboratory reference values for serum CK do not consider race.

Transient elevations in CK levels are common after reversible causes of muscle injury such as trauma (including injections or needle electromyography), vigorous exertion, or even muscle cramping. A serum sample drawn after electromyography (EMG) in a normal patient will increase up to three fold within the next 24 hours and may show a false positive CK result suggesting myopathy. Therefore, it is important to draw CK levels before EMG studies. In one report, CK levels rose from a mean baseline of 53 U/L in 10 patients to a maximum mean CK of 91 U/L 12 to 24 hours after an EMG; a return to baseline occurred after 48 to 72 hours.9

Vigorous exertion may increase serum CK levels transiently. After a marathon, CK levels in 7 runners were reported to maximally increase 24 hours after the race to a mean of 1404 U/L (range 683 to 2261 U/L).10 In this study, mean CK levels approached baseline after about 1 week. In general, one week of avoidance of exertional activity should be sufficient to ensure accurate measurement of CK levels in a frequently exercising patient.

Excessive skeletal muscle exertion resulting in CK elevations can also be seen in certain non- neuromuscular pathological events such as neuroleptic malignant syndrome, convulsive seizures, acute psychosis and violent behavior.2

A single non-pathological cramp can also cause a substantial rise in CK levels. In one published case,11 after a single severe cramp in a gastrocnemius muscle lasting several minutes, serum CK elevated from 117 IU/L (normal <220 IU/L) to 229 IU/L within 6 hours after the cramp and to a peak of 534 IU/L by 30 hours. Serum CK levels returned to normal after 5 days.

Creatine kinase monitoring in sport medicine

Paola Brancaccio*,{dagger}, Nicola Maffulli{ddagger} and Francesco Mario Limongelli{dagger}

{dagger} Department of Experimental Medicine—Sport Medicine, Centre of Excellence of Cardiovascular Disease, Seconda Università di Napoli, Napoli, Italy
{ddagger} Department of Trauma and Orthopaedic Surgery, Keele University School of Medicine, Thornburrow Drive, Hartshill, Stoke on Trent ST4 7QB Staffs, UK

Areas of general agreement: Total creatine kinase (CK) levels depend on age, gender, race, muscle mass, physical activity and climatic condition. High levels of serum CK in apparently healthy subjects may be correlated with physical training status, as they depend on sarcomeric damage: strenuous exercise that damages skeletal muscle cellsresults in increased total serum CK. The highest post-exercise serum enzyme activities are found after prolonged exercise such as ultradistance marathon running or weight-bearing exercises and downhill running, which include eccentric muscular contractions.Total serum CK activity is markedly elevated for 24 h after the exercise bout and, when patients rest, it gradually returns to basal levels. Persistently increased serum CK levels are occasionally encountered in healthy individuals and are also markedly increased in the pre-clinical stages of muscle diseases.

Areas that are controversial: Some authors, studying subjects with high levels of CK at rest, observed that, years later, subjects developed muscle weakness and suggested that early myopathy may be asymptomatic. Others demonstrated that, in most of these patients, hyperCKemia probably does not imply disease. In many instances, the diagnosis is not formulated following routine examination with the patients at rest, as symptoms become manifest only after exercise. Someauthors think that strength training seems to be safe for patients with myopathy, even though the evidence for routine exercise prescription is still insufficient. Others believe that, in these conditions, intense prolonged exercise may produce negative effects, as it does not induce the physiological muscle adaptations to physical training given the continuous loss of muscle proteins.

Growing points: High CK serum levels in athletes following absolute rest and without any further predisposing factors should prompt a full diagnostic workup with special regards to signs of muscle weakness or other simple signs that, in both athletes and sedentary subjects, are not always promptly evident. These signs may indicate subclinical muscle disease, which training loads may evidence through the onset of profound fatigue. It is probably safe to counsel athletes with suspected myopathy to continue to undertake physical activity at a lower intensity, so as to prevent muscle damage from high intensity exercise and allow ample recovery to favour adequate recovery.

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