From the Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden PHYSIOLOGY OF ADVENTURE RACING – WITH EMPHASIS ON CIRCULATORY RESPONSE AND CARDIAC FATIGUE

1 " We'll go because it's Thursday, and we'll go to wish everybody a Very Happy Thursday. " Winnie-the-Pooh 2 ABSTRACT The overall aims of this thesis were to elucidate the circulatory responses to ultra-endurance exercise (Adventure Racing), and furthermore, to contribute to the clarification of the so called " exercise-induced cardiac fatigue " in relation to said exercise. An Adventure race (AR) varies in duration from six hours to over six days, in which the participants have to navigate through a number of checkpoints over a pre-set course, using a combination of three or more endurance/outdoor sports, e.g., cycling, running, and kayaking. This thesis is based on the results from four different protocols; 12-and 24-h (n = 8 and 9, respectively) in a controlled setting with fixed exercise intensity, and 53-h and 5-7-day (n = 15 in each) in field setting under race conditions. The subjects in all protocols were experienced adventure racing athletes, competitive at elite level. Study I and II address the circulatory responses and cardiovascular drift, using methods for monitoring heart rate (HR), oxygen uptake (VO 2), cardiac output (non-invasive re-breathing) and blood pressure, during ergometer cycling at fixed steady state work rate at periods before, during and after the ultra-endurance exercise. In Study III and IV we examined the possible presence of exercise-induced cardiac fatigue after a 5-7-day AR, from two different perspectives. In Study III analyses were performed with biochemical methods to determine circulating levels of cardiac specific biomarkers (i.e., creatine kinase isoenzyme MB (CK-MB), troponin I, B-type natriuretic peptide (BNP) and N-terminal prohormonal B-type natriuretic peptide (NT-proBNP)). We also made an attempt to relate increases in biomarkers to rated relative performance. In Study IV we used tissue velocity imaging (TVI) (VIVID I, GE VingMed Ultrasound, Norway) to determine whether the high workload (extreme duration) would induce signs of functional cardiac fatigue similar to those that occur in skeletal muscle, i.e., decreased peak systolic velocities. Using conventional echocardiography we also evaluated whether the hearts of experienced ultra-endurance athletes are larger than the normal upper limit. The central circulation changed in several steps in response to ultra-endurance exercise. Compared to initial levels, VO 2 was increased at every time-point measured. The increase was attributed to peripheral adaptations, confirmed by a close correlation between change in VO 2 and change in arterio-venous oxygen difference. The first step of the circulatory response was typical of normal (early) …