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Reversed drift in heart rate but increased oxygen uptake at fixed work rate during 24 h ultra-endurance exercise.
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.ORCID iD: 0000-0002-0642-4838
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
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2010 (English)In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 20, no 2, 298-304 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we report a reversed drift in heart rate (HR) but increased oxygen uptake (VO(2)) during ultra-endurance exercise. Nine well-trained male athletes performed 24-h exercise in a controlled laboratory setting, with alternating blocks of kayaking, running and cycling. Each block included 110 min of exercise and 10 min of rest, with an average work intensity of approximately 55% of respective VO(2peak). Blood samples were taken and HR and VO(2) measured every 6th hour during steady-state cycling at fixed work rate. As assumed HR was increased at 6 h by 15 +/- 6 beats/min compared with initial level (0 h). Thereafter the drift did not progress continuously, but instead unexpectedly returned toward initial values, although the plasma levels of catecholamines increased continuously during exercise. VO(2) was increased by 0.22 +/- 0.15 L/min (10%) at 6 h and 0.37 +/- 0.18 L/min (17%) at 12 h compared with 0 h, and thereafter remained stable. This implies an increased oxygen pulse (VO(2)/HR) by approximately 10% at the last half of the 24-h exercise compared with 0 h. Consequently, sole use of HR would give inaccurate estimates of exercise intensity and energy expenditure during endurance exercise lasting more than 6 h, and different patterns of cardiovascular drift need to be taken into account.

Place, publisher, year, edition, pages
2010. Vol. 20, no 2, 298-304 p.
National Category
Physiology
Research subject
Medicine/Technology
Identifiers
URN: urn:nbn:se:gih:diva-939DOI: 10.1111/j.1600-0838.2009.00878.xPubMedID: 19486489OAI: oai:DiVA.org:gih-939DiVA: diva2:322080
Projects
Physiology of Adventure Racing
Available from: 2010-06-03 Created: 2009-07-14 Last updated: 2017-03-31Bibliographically approved
In thesis
1. Physiology of Adventure Racing: with emphasis on circulatory response and cardiac fatigue
Open this publication in new window or tab >>Physiology of Adventure Racing: with emphasis on circulatory response and cardiac fatigue
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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 check-points 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 (VO2), 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, VO2 was increased at every time-point measured. The increase was attributed to peripheral adaptations, confirmed by a close correlation between change in VO2 and change in arteriovenous oxygen difference. The first step of the circulatory response was typical of normal (early) cardiovascular drift, with increased HR and concomitantly decreased stroke volume (SV) and oxygen pulse (VO2/HR), occurring over the first 4-6 h. The second step, which continued until approximately 12h, included reversed HR-drift, with normalisation of SV and VO2/HR. When exercise continued for 50 h a late cardiovascular drift was noted, characterised by increased VO2/HR, (indicating more efficient energy distribution), decreased peripheral resistance, increased SV, and decreased work of the heart. Since cardiac output was maintained at all-time points we interpret the changes as physiologically appropriate adaptations. Our findings in Study III point towards a distinction between the clinical/pathological and the physiological/exercise-induced release of cardiac biomarkers. The results imply that troponin and CKMB lack relevance in the (healthy) exercise setting, but that BNP, or NT-proBNP adjusted for exercise duration, might be a relevant indicator for impairment of exercise performance. High levels of NTproBNP, up to 2500 ng · l -1 , can be present after ultra-endurance exercise in healthy athletes without any subjective signs or clinical symptoms of heart failure. However, these high levels of NT-proBNP seemed to be associated with decreased relative exercise performance, and might be an indicator of the cardiac fatigue that has previously been described after endurance exercise. Study IV revealed that the sizes of the hearts (left ventricle) of all of our ultra-endurance athletes were within normal limits. The measurements of peak systolic velocities showed (for group average) no signs of cardiac fatigue even after 6 days of continuous exercise. This discrepancy between ours and other studies, involving e.g., marathon or triathlon, might reflect the fact that this type of exercise is performed at relatively low average intensity, suggesting that the intensity, rather than the duration, of exercise is the primary determinant of cardiac fatigue.

Place, publisher, year, edition, pages
Stockholm: Karolinska Institutet, 2011. 112 p.
Keyword
cardiovascular drift, cardiac fatigue, adventure race, cardiac biomarkers, cardoac function, exercise echocardiography
National Category
Physiology Cardiac and Cardiovascular Systems Sport and Fitness Sciences
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-1754 (URN)978-91-7457-262-9 (ISBN)
Public defence
2011-03-25, Aulan GIH, Lidingövägen 1, Stockholm, 09:00 (English)
Opponent
Supervisors
Projects
Physiology of Adventure Racing
Available from: 2011-03-04 Created: 2011-03-03 Last updated: 2014-10-17Bibliographically approved

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Mattsson, C. MikaelEnqvist, Jonas KEkblom, Björn
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