AUTHOR=Weippert Matthias , Behrens Martin , Mau-Moeller Anett , Bruhn Sven , Behrens Kristin 

TITLE=Relationship Between Morning Heart Rate Variability and Creatine Kinase Response During Intensified Training in Recreational Endurance Athletes

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.01267

DOI=10.3389/fphys.2018.01267

ISSN=1664-042X

ABSTRACT=<p>Specific physiological responses and their relationship were analyzed in 12 recreational endurance athletes (43.8 ± 7.9 years) during a period of intensified cycling training. Heart rate (HR), HR variability (HRV), serum creatine kinase (S-CK) and haematocrit (Hct) were measured in the mornings before (PRE) and following three consecutive days of intensified training (POST 1–3). Morning HR increased during this period (PRE: 52.2 ± 6.7 bpm, POST 1: 58.8 ± 7.0 bpm, POST 2: 58.5 ± 8.1 bpm, POST 3: 57.9 ± 7.2 bpm; <italic>F</italic>(3,33) = 11.182, <italic>p</italic> &lt; 0.001, η<sub>p</sub><sup>2</sup> = 0.554). Parasympathetic HRV indices decreased from PRE to POST (<italic>F</italic>(3,33) ≥ 11.588, <italic>p</italic> &lt; 0.001, η<sub>p</sub><sup>2</sup> ≥ 0.563), no effect was found for sympathetically modulated HRV (<italic>F</italic>(3,33) = 2.287, <italic>p</italic> = 0.101, η<sub>p</sub><sup>2</sup> = 0.203). Hct decreased (PRE: 49.9 ± 4.0%, POST 1: 46.5 ± 5.1%, POST 2: 45.5 ± 3.8%, POST 3: 43.2 ± 3.4%; <italic>F</italic>(3,33) = 11.909, <italic>p</italic> &lt; 0.001, η<sub>p</sub><sup>2</sup> = 0.520) and S-CK increased during the training period (PRE: 90.0 ± 32.1 U/L, POST 1: 334.7 ± 487.6 U/L, POST 2: 260.1 ± 303.4 U/L, POST 3: 225.1 ± 258.8 U/L; <italic>F</italic>(3,33) = 3.996, <italic>p</italic> = 0.017, η<sub>p</sub><sup>2</sup> = 0.285). S-CK release was associated with HR (<italic>r</italic> = 0.453, <italic>p</italic> = 0.002, <italic>n</italic> = 44), RMSSD (<italic>r</italic> = −0.494, <italic>p</italic> = 0.001, <italic>n</italic> = 44) and HF-Power (<italic>r</italic> = −0.490, <italic>p</italic> = 0.001, <italic>n</italic> = 44). A period of intensified training was associated with haemodilution, parasympathetic withdrawal and S-CK-increase. Cardiac autonomic control at morning rest correlated with the S-CK-release; and thus, may serve as a practical mean to complementary monitor and prescribe training load in this population.</p>