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Letters to the Editor |
1 Sezione di Chimica ClinicaDipartimento di ScienzeMorfologico-BiomedicheUniversità di Verona, Italy
2 Sezione di Scienze MotorieDipartimento di ScienzeNeurologiche e della Visione Università di Verona, Italy
3 Istituto Galeazzi e Università di Milano Italy
aAddress correspondence to this author at: Sezione di Chimica Clinica, Dipartimento di Scienze, Morfologico-Biomediche, Università degli Studi di Verona, Ospedale Policlinico G.B. Rossi, Piazzale Scuro, 10, 37134, Verona, Italy, Fax 0039-045-8201889, e-mail ulippi{at}tin.it
To the Editor:
Parathyroid hormone (PTH) and osteocalcin (OC) play important roles in bone remodeling and bone metabolism. Although the physiological functions and clinical significance of these markers are well established, the influence of other biological variables aside from diurnal and seasonal variability has been less well investigated(1). Because little information is available on the kinetics of such markers after physical exercise, we measured PTH and OC in 15 athletes performing a half-marathon run. The study population consisted in 15 healthy trained white males, (mean age, 47 years) who had been engaged in specific endurance training for at least 5 years. Participants performed a 21-km, half-marathon run under competition conditions, while equipped with a heart-rate monitor [mean (SE) VO2 max 85% (3%)]. Prior to the race, preexercise baseline fasting blood samples were collected from the volunteers after a 48-h rest from the last training, 30 min before they warmed up for the race. Post exercise samples were collected immediately after the race, and 3 h, 6 h, and 24 h thereafter. All study participants gave informed consent for being tested, and the study was approved by the ethics committee. Blood was collected in vacuum tubes containing no additives (Becton Dickinson) and centrifuged at 1500g for 10 min at room temperature, and the serum was immediately analyzed. OC and intact PTH were measured on an Elecsys 2010 by electrochemiluminescence immunoassays (Roche Diagnostics GmbH). We used the N-MID Osteocalcin assay that is specific for intact OC (amino acids 1–49) and the main N-terminal fragment (amino acids 1–43) resulting from proteolytic cleavage after blood collection. Among markers of bone turnover, OC was selected to verify the effects of physical training on osteoblast function, because it may indirectly reflect acute changes in cortisol, and it is currently considered an indirect marker of growth hormone abuse in sports(2). The total assay imprecision (CV) was 1.1%–5.9% for OC and 1.7%–5.5% for intact PTH, respectively(3). The age- and sex-specific reference ranges were 1.6–6.9 pmol/L for PTH and 14–42 µg/L for OC, respectively. Hematocrit and hemoglobin were measured on an Advia 120 (Bayer Diagnostics). Because the estimated decrease in total body water does not differ from the percentage plasma volume change (%PVC), results were adjusted for the %PVC, calculated from pre- and postexercise levels of hematocrit and hemoglobin(4). The Wilcoxon signed-rank test was used to evaluate the significance of exercise-induced variations during the study period. Data with a nongaussian distribution were normalized using a logarithmic transformation before analysis, and the level of statistical significance was set at P < 0.05. Data are presented as geometric mean (SE).
The concentrations of both markers increased significantly by nearly 1.2-fold (OC) and 2.1-fold (PTH) immediately after the run, but 3 h thereafter rapidly returned to values comparable to those measured before the run (Table 1
). The number of participants with values above the respective reference ranges remained stable throughout the study period for OC (n = 2, 13%), whereas it increased from 0 (0%) to 6 (40%) immediately after the run and returned to 0 (0%) 3 h thereafter for PTH.
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These results support the hypothesis that a 21-km run produces an acute and transitory increase of both PTH and OC, which is completely reversed 3 h thereafter. Although earlier studies have investigated PTH and OC after strenuous aerobic exercise, especially marathon and ultramarathon running(5), no information is available on the kinetics of these markers following moderately strenuous aerobic physical exercise, such as a 21-km half-marathon run, a distance that is more typically accessible for a general population of active individuals. Although Mouzopoulos et al. observed that PTH concentrations increase by nearly 1.3-fold immediately after 245 km of marathon running, these investigators also reported a significant decrease in OC concentrations. Such differences may be due to different preanalytical conditions (sample matrix and storage) or intensity and duration of the run. The transient suppression in osteoblast function occurring during an ultramarathon run, which has been attributed to increases in cortisol and PTH concentrations(5), might not occur during shorter-distance runs. Perhaps athletes should be advised to run a half or a fraction of a marathon to avoid potential harmful effects of strenuous endurance exercise. Because OC is a marker of growth-hormone abuse in sports(2), such variations should be acknowledged when evaluating the athletes for clinical or antidoping purposes, because these measurement results should be interpreted as physiological responses to exercise rather than pathology or consequences of unfair practices.
Acknowledgments
Grant/Funding Support: None declared.
Financial Disclosures: None declared.
References
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