Cardiac troponin increases are common in adult marathon finishers. However, data on troponin values for young marathon runners are scarce. Forty young runners (20 healthy male and 20 female) 13 to 17 years old participated in this study. Blood samples were taken before, immediately after, and 24 hours after the race for determination of cardiac troponin T (cTnT) and troponin I (cTnI). Thirty-seven runners completed the race with a mean finishing time of 4 hours 53 minutes. No participant developed an adverse medical event during or after the race. In 30 of 37 participants, levels of cTnT and/or cTnI exceeded upper reference limits of 0.01 and 0.1 ng/ml immediately after the race, and in 3 participants these levels were even higher than the reference range for acute myocardial infarction (>0.1 and >0.5 ng/ml for cTnT and cTnI, respectively). Twenty-four hours after the race no participant had troponin levels exceeding the upper reference limits. Average increases of troponin levels did not differ between sexes. In conclusion, this is the first study to show that cardiac troponin levels increase to a similar extent in male and female adolescent marathon runners as observed in adults. Rapid recovery of troponin levels after a race is indicative of a physiologic rather than a pathologic response.
In recent years marathon running has become increasingly popular. However, runners are often not well prepared with the consequences of medical emergencies during or after the race. There are only very limited (patho)physiologic data on young marathon runners. Although marathon running in adolescents and even children seems to be safe, information on potential risks to the heart is scarce and conflicting for adults and practically missing for young marathon runners. Data on increased cardiac troponin levels in adolescent runners have been reported after prolonged running in laboratory-based settings and after running 21 km. Interpretation of these transient increases of cardiac troponins in adolescent runners is limited by small samples, the restriction to men runners, and investigating distances up to 21 km or treadmill running. Therefore, in this study cardiac troponins were assessed for the first time in a large sample of young male and female runners competing a standard marathon distance.
Methods
Forty healthy (20 male and 20 female) adolescents 13 and 17 years old volunteered to participate in this study. Baseline characteristics are listed in Table 1 . Participants had no previous marathon experience but all were regular runners from the Khon Kaen Sport School, Khon Kaen, Thailand. They had to undergo routine physical examination including electrocardiographic records. No cardiovascular abnormalities were identified. Each runner had an approximate mean training load of 40 km/week, but active training years varied depending on age ( Table 1 ). Two weeks before the marathon all participants performed submaximal exercise testing to estimate maximum oxygen consumption according to Astrand et al. Participants and their parents gave written informed consent for participation in the study. The experimental protocol was approved by the Khon Kaen University ethics committee for human research.
| Variable | Male (n = 20) | Female (n = 20) |
|---|---|---|
| Age (years) | 16.7 ± 0.5 | 14.7 ± 1.3 ⁎ |
| Body mass (kg) | 61.5 ± 5.2 | 45.5 ± 6.6 ⁎ |
| Height (cm) | 173.5 ± 6.0 | 158.3 ± 6.3 ⁎ |
| Body mass index (kg/m 2 ) | 18.0 ± 1.7 | 20.3 ± 1.7 ⁎ |
| Heart rate (beats/min) | 68.7 ± 6.7 | 71.1 ± 8.5 |
| Systolic blood pressure (mm Hg) | 111.9 ± 5.6 | 107.9 ± 8.9 |
| Diastolic blood pressure (mm Hg) | 67.2 ± 6.7 | 63.5 ± 7.4 |
| Forced vital capacity (L) | 3.2 ± 0.2 | 2.5 ± 0.3 ⁎ |
| Calculated maximal oxygen uptake (ml/min/kg) | 66.2 ± 3.8 | 54.8 ± 6.1 ⁎ |
| Running history (months) | 35 ± 15 | 24 ± 8 ⁎ |
The Khon Kaen International Marathon is certified by the International Association of Athletics Federations and Athletics Association of Thailand, and the route is certified by the Association of International Marathon and Road Races. The 42.2-km relatively flat course (altitude displacement 40 m) consisted of running 10 km on asphalt and the remaining 32.2 km on concrete. Fluids were freely available at drink stations every 5 km along the way. Available fluids were water and sport drinks (electrolyte drink; Sponsor, Bangkok, Thailand). All runners were advised to run at an individual pace conforming to their running ability. They were free to stop whenever they perceived overexertion. Participants were continuously supervised by a medical doctor.
Venous blood samples (10 ml) were taken in the early morning 2 days before the marathon, immediately after the race, and 24 hours after the race. Blood was taken from the antecubital vein by medical laboratory assistants from the faculty of associated medical science, Khon Kaen University. All samples were centrifuged immediately and transported on dry ice to the laboratory at Srinakarin Hospital, faculties of medical science and associated medical science, Khon Kaen University.
A complete blood cell count was performed with an Xs-800i analyzer (Sysmex Corp., Kobe, Japan) for determinations of red blood cell count, mean corpuscular volume, mean corpuscular hemoglobin concentration, red cell distribution width, white blood cell count, and platelet count. Creatine kinase, creatine kinase-MB, myoglobin, and serum cardiac troponin T (cTnT) were analyzed using an Automate Chemistry Cobas 6000 analyzer (Roche Diagnostics, Indianapolis, Indiana). Serum cardiac troponin I (cTnI) analysis was performed using an Automate Beckman (Fullerton, California) CX4.
All values are expressed as mean ± SD. Analysis of variance for repeated measures and post hoc t tests with Bonferroni correction were used to evaluate changes of biomarkers from baseline to postrace values. Pearson correlation analyses were applied to examine the relation among subject characteristics, biomarkers, and running history. A p value <0.05 was considered statistically significant. Statistical analysis was performed using SPSS 19 (SPSS, Inc., Chicago, Illinois).
Results
The Eighth Khon Kaen International Marathon started at 4:15 a.m. on January 23, 2011. On the race day ambient air temperature was 16.6°C to 24.5°C and relative humidity during the race was 45% to 82%. Thirty-seven participants completed the marathon and the mean finishing time was 4 hours 53 minutes 35 seconds (range 3 hours 17 minutes 9 seconds to 6 hours 00 minute 1 second). No participant developed an adverse medical event requiring medical attention during or after the race. Before the race no participant showed any abnormal electrocardiogram. Three participants dropped out because of problems with their shoes. Thus, 37 subjects were considered for further analyses.
Complete blood cell count parameters before, immediately after, and 24 hours after the race are presented in Table 2 . There were statistically significant differences in all measured parameters over time except for mean corpuscular hemoglobin. Table 3 lists markers of cardiac and skeletal muscle damage before, immediately after, and 24 hours after the race separated by sex. Mean values for cardiac troponins did not differ between boys and girls. There were statistically significant changes in all parameters over time. Post hoc tests showed significant increases for levels of myoglobin, creatine kinase, creatine kinase-MB, cTnT, and cTnI immediately and 24 hours after the race. In 30 of 37 participants levels of cTnT and cTnI exceeded the upper reference limits of 0.01 and 0.1 ng/ml, respectively. One of the 37 subjects had values higher than the acute myocardial infarction (AMI) cutoff for cTnT (0.1 ng/ml; Figure 1 ) and 2 subjects had higher values than the AMI cutoff for cTnI (0.5 ng/ml; Figure 2 ). Twenty-four hours after the race no participant presented troponin levels exceeding the upper reference limits.
| Variable | Before Marathon | After Marathon | ANOVA | |
|---|---|---|---|---|
| Immediately | 24 Hours | |||
| White blood cell count (10 3 /μl) | 7.4 ± 1.7 | 11.5 ± 3.2 ⁎ | 7.7 ± 1.9 ‡ | <0.001 |
| Hemoglobin (g/dl) | 13.9 ± 1.5 | 13.2 ± 1.5 ⁎ | 13.4 ± 1.3 † ‡ | <0.001 |
| Hematocrit (%) | 41.8 ± 3.9 | 39.2 ± 4.1 ⁎ | 40.5 ± 3.6 † ‡ | <0.001 |
| Red blood cell count (10 6 /μl) | 5.47 ± 0.51 | 5.15 ± 0.42 ⁎ | 5.24 ± 0.45 † ‡ | <0.001 |
| Platelet count (10 3 /μl) | 299.3 ± 59.9 | 305.4 ± 57.1 | 284.0 ± 51.0 ‡ | 0.006 |
| Mean corpuscular volume (fl) | 77.1 ± 8.9 | 76.4 ± 8.7 ⁎ | 77.5 ± 8.8 ‡ | 0.003 |
| Mean corpuscular hemoglobin (pg) | 25.6 ± 3.1 | 25.6 ± 3.1 | 25.8 ± 3.1 | 0.25 |
| Mean corpuscular hemoglobin concentration (g/dl) | 33.1 ± 0.9 | 33.5 ± 0.9 ⁎ | 33.3 ± 0.9 ‡ | <0.001 |
| SD of red cell distribution width (fl) | 38.5 ± 2.2 | 36.5 ± 4.5 ⁎ | 38.1 ± 2.2 | 0.004 |
| Coefficient variation of red cell distribution width (%) | 14.1 ± 2.5 | 13.8 ± 2.4 ⁎ | 14.0 ± 2.5 | <0.001 |
| Total white blood cell count | ||||
| Neutrophils (%) | 54.5 ± 8.4 | 73.5 ± 10.3 ⁎ | 62.1 ± 10.3 † ‡ | <0.001 |
| Lymphocytes (%) | 36.1 ± 9.0 | 21.5 ± 9.6 ⁎ | 29.2 ± 10.0 † ‡ | <0.001 |
| Monocytes (%) | 6.43 ± 1.86 | 4.43 ± 1.25 ⁎ | 5.67 ± 1.35 † ‡ | <0.001 |
| Eosinophils (%) | 2.89 ± 2.27 | 0.56 ± 1.25 ⁎ | 2.81 ± 2.60 ‡ | <0.001 |
| Basophils (%) | 0.11 ± 0.31 | 0.00 ± 0 | 0.16 ± 0.37 ‡ | 0.011 |
⁎ Significant difference before versus immediately after marathon.
† Significant difference before versus 24 hours after marathon.
‡ Significant difference immediately after versus 24 hours after marathon.
| Variable | Male (n = 19) | Female (n = 18) | p Value Between Sexes | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Before Marathon | Immediately After Marathon | 24 Hours After Marathon | p Value | Before Marathon | Immediately After Marathon | 24 Hours After Marathon | p Value | ||
| Myoglobin (μg/L) | 72.5 ± 15.45 | 713.9 ± 114.3 ⁎ | 371.1 ± 72.3 † ‡ | <0.001 | 76.7 ± 10.2 | 792.7 ± 108.6 ⁎ | 388.1 ± 53.4 † ‡ | <0.001 | 0.07 |
| Creatine kinase (U/L) | 356.8 ± 260.0 | 821.9 ± 368.0 ⁎ | 1,254.5 ± 1,035.9 † | <0.001 | 151.7 ± 66.7 | 548.6 ± 398.4 ⁎ | 630.4 ± 660.0 † | <0.001 | 0.31 |
| Creatine kinase-MB (U/L) | 19.4 ± 4.9 | 25.8 ± 8.0 ⁎ | 38.6 ± 20.8 † ‡ | <0.001 | 19.5 ± 16.4 | 26.0 ± 22.1 ⁎ | 30.1 ± 19.8 † | 0.001 | 0.24 |
| Cardiac troponin I (ng/ml) | 0.013 ± 0.005 | 0.212 ± 0.105 ⁎ | 0.028 ± 0.013 † ‡ | 0.006 | 0.011 ± 0.003 | 0.211 ± 0.161 † | 0.023 ± 0.014 † ‡ | 0.018 | 0.70 |
| Cardiac troponin T (ng/ml) | 0.004 ± 0.002 | 0.013 ± 0.011 ⁎ | 0.005 ± 0.003 ‡ | <0.001 | 0.003 ± 0.000 | 0.024 ± 0.028 ⁎ | 0.005 ± 0.003 † ‡ | <0.001 | 0.27 |
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