Introduction:

The kinetics of cell-free circulating DNA (cfDNA) concentrations is of importance for many biomedical disciplines in clinical medicine and exercise physiology. Exercise provides a practicable model for studying the kinetics of cfDNA in vivo. Different studies have shown increases in plasma concentrations of cfDNA induced by intensive acute or chronic exercise. Until today the mechanism of cfDNA accumulations during and after exercise remains unexplained. The aim of the study was the assessment of a minimal-invasive method to compare cfDNA and lactate levels of healthy subjects in response to an incremental treadmill test.

Methods:

Subjects performed an incremental treadmill test in the Department of Sports Medicine Mainz. Minimal blood samples were collected from the earlobe for lactate and from the fingertip for cfDNA measurement before, every three minutes during and after the exercise test. Lactate levels were determined with the EKF Biosen 5140. cfDNA was quantified by a new direct quantitative real-time PCR method.

Results:

cfDNA kinetics over the course of the incremental exercise was strikingly similar to the kinetics of lactate. The individual anaerobic threshold (IAT) according to the baseline threshold concept either determined by interpolation of lactate or cfDNA values presented a positive correlation.

Conclusion:

The lactate-like association of cfDNA concentrations with workload implicates cfDNA as an interesting marker for metabolic exhaustion. We discuss here why the origin of cfDNA concentrations observed during incremental exercise cannot be related with an on-going process of necrosis or apoptosis, but is rather related to humoral or physical factors associated with exhaustion.