From JAMA; Vol. 282 No.19, November 17, 1999

Regular Exercise and Subclinical Myocardial Injury During Prolonged
Aerobic Exercise  
To the Editor: Physicians increasingly are encouraged to prescribe
moderate or vigorous intensity physical activity for their patients.
However, prolonged
aerobic exercise may cause myocardial damage manifested immediately
after exercise as a rise in cardiac troponin T (cTnT) and cardiac
troponin I levels and wall motion abnormalities detected by
echocardiography. We conducted a study to determine
whether modest physical activity is sufficient to protect against
subclinical myocardial injury caused by excessive exercise. <snip>

Blood samples were collected from 36 athletes (34 men, 2 women; mean
[SD] age 38.9 [6.2] years; none with cardiovascular disease risk
factors)24 hours before and 2 hours after an Alpine marathon and an
Alpine cross-country marathon, respectively.
The start and finish of the marathon is in Galtür (Tirol, Austria;
1584 m above sea level);<snip>

Capillary cTnT level was measured by immunoassay in strip format
<snip> with the Cardiac Reader (Roche Diagnostics).4 <SNIP> A
physician reviewed the medical history and performed a physical
examination, including brachial artery blood pressure measurement,
echocardiography, and electrocardiography, in participants with
increased cTnT levels 2 days after exercise. Blood samples were
drawn in the morning after an overnight fast. All samples were
analyzed for lipids, lipoproteins, and cTnT level. <snip>

All participants finished the marathons. The mean (SD) running time
was 238 (28) minutes for the Alpine marathon (n = 24) and 139 (13)
minutes for the Alpine cross-country marathon (n = 12). No subject
had a detectable cTnT level in the prerace samples. However, after
the races 4 subjects had marked increases in cTnT levels (0.11-0.2
µg/L). Cross-country times for the 4 participants were 194, 227,
229, and  143 minutes, indicating no difference in performance times
compared with those subjects who did not have elevated cTnT levels.
However, these 4 subjects (mean
 [SD] age, 36.2 [0.8] years) had trained 1 to 3 times a week,
whereas all the other individuals exercised 5 to 6 times a week. The
4 participants who had marked increases in cTnT levels had received
medical clearance. No cardiovascular abnormalities or cardiovascular
disease risk factors were identified. No subject had detectable cTnT
levels 2 days after exercise.
                            
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