Cell-free DNA kinetics in response to muscle-damaging exercise: A drop jump study

Abstract

A significant increase in circulating cell-free DNA (cfDNA) occurs with physical exercise, which depends on the type of exertion and the duration. The aims of this study were as follows: (1) to investigate the time course of cfDNA and conventional markers of muscle damage from immediately after to 96 h after muscle-damaging exercise; and (2) to investigate the relationship between cfDNA and indicators of primary (low-frequency fatigue and maximal voluntary isometric contraction) and secondary (creatine kinase and delayed-onset muscle soreness) muscle damage in young healthy males. Fourteen participants (age, 22 ± 2 years; weight, 84.4 ± 11.2 kg; height, 184.0 ± 7.4 cm) performed 50 intermittent drop jumps at 20 s intervals. We measured cfDNA and creatine kinase concentrations, maximal voluntary isometric contraction torque, low-frequency fatigue and delayed-onset muscle soreness before and at several time points up to 96 h after exercise. Plasma cfDNA levels increased from immediately postexercise until 72 h postexercise (P < 0.01). Elevation of postexercise cfDNA was correlated with both more pronounced low-frequency fatigue (r = -0.52, P = 3.4 × 10^-11) and delayed-onset muscle soreness (r = 0.32, P = 0.00019). Levels of cfDNA change in response to severe primary and secondary muscle damage after exercise. Levels of cfDNA exhibit a stronger correlation with variables related to primary muscle damage than to secondary muscle damage, suggesting that cfDNA is a more sensitive marker of acute loss of muscle function than of secondary inflammation or damaged muscle fibres.

Keywords: blood markers; cell‐free DNA; eccentric exercise; muscle damage.

FIGURE 1

(a) Experimental design. (b) Neuromuscular testing. (c) Position of electrodes placed on the quadriceps. Abbreviations: BS, blood samples; DOMS, delayed‐onset muscle soreness; MVIC, maximal voluntary isometric contraction; NT, neuromuscular testing; P20, electrical stimulation (1 s stimulation) at 20 Hz; P100, electrical stimulation (1 s stimulation) at 100 Hz; TT, 250 ms test train stimulation at 100 Hz.

FIGURE 2

(a) MVC torque. (b) P20 torque. (c) P100 torque. (d) CAR. Data are expressed relative to baseline values, which were set to 100% in each experiment. Data are shown as means ± SD and individual values, n = 14. *P < 0.05, **P < 0.01: differences from the Pre time point. Abbreviations: CAR, central activation ratio; MVIC, maximal voluntary isometric contraction; P20, 1 s stimulation at 20 Hz; P100, 1 s stimulation at 100 Hz.

FIGURE 3

Low‐frequency fatigue (ratio of 20 Hz to 100 Hz electrically stimulated torques). Data are expressed relative to baseline values, which were set to 100% in each experiment. Data are shown as means ± SD and individual values, n = 14.**P < 0.01: differences from the Pre time point.

FIGURE 4

(a) CK. (b) DOMS (0−10 scale). Data are shown as mean ± SD and individual values, n = 14. *P < 0.05, **P < 0.01 and ***P < 0.001: differences from the Pre time point. Abbreviations: CK, creatine kinase; DOMS, delayed‐onset muscle soreness.

FIGURE 5

Cell‐free DNA (90 bp) kinetics over the assessment period. Data are shown as means ± SD on a logarithmic scale, n = 14. *P < 0.05 and **P < 0.01: differences from the Pre time point. Abbreviation: cfDNA, cell‐free DNA.

FIGURE 6

(a) Correlation between low‐frequency fatigue (ratio of 20 Hz to 100 Hz electrically stimulated torques) and log₁₀‐transformed cfDNA, n = 14. (b) Correlation between MVIC torque and log₁₀‐transformed cfDNA. (c) Correlation between P20 torque and log₁₀‐transformed cfDNA, n = 14. (d) Correlation between P100 torque and log₁₀‐transformed cfDNA, n = 14. (e) Correlation between log₁₀‐transformed CK and log₁₀‐transformed cfDNA, n = 14. (f) Correlation between DOMS and log₁₀‐transformed cfDNA, n = 14. The lines represent the linear trend. The significance of the correlation and r values are displayed on the charts. Abbreviations: cfDNA, cell‐free DNA; CK, creatine kinase; DOMS, delayed‐onset muscle soreness; MVIC, maximal voluntary isometric contraction; P20, 1 s stimulation at 20 Hz; P100, 1 s stimulation at 100 Hz.