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Unexpected cardiovascular response during ultra-endurance exercise.
Swedish School of Sport and Health Sciences, GIH. (Adventure Racing Research GIH samt Institutionen för fysiologi och farmakologi (FyFa), Karolinska Institutet)ORCID iD: 0000-0002-0642-4838
Swedish School of Sport and Health Sciences, GIH. (Adventure Racing Research)
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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2008 (English)In: 13th Annual Congress of the European College of Sport Science (ECSS), Estoril, Lissabon, Portugal.: Sport Science by the sea, 2008, 142- p.Conference paper, (Other academic)
Abstract [en]

During prolonged exercise at fixed work rate heart rate (HR) increases slowly with concomitant decrease in stroke volume (SV) in order to maintain cardiac output. Simultaneously, an increased oxygen uptake (VO2) occurs. In this paper we report an unexpected and previously not observed cardiovascular response to ultra-endurance exercise. Nine well-trained male athletes performed 24-h exercise in a controlled laboratory setting, with altering blocks of kayaking, running and cycling. Each block consisted of 110 min of exercise and 10 min of rest. Measurements (HR, VO2 and blood samples) were conducted during cycling at fixed work rate every 6th hour. The average work intensity was approximately 55 % of respective VO2peak. HR was increased at 6 h with 15 beats/min (13 %) compared to pre-exercise (Pre-Ex), but thereafter unexpectedly returned towards initial values. VO2 on the other hand was increased with 0.22 l/min (10 %) at 6 h and 0.37 l/min (17 %) at 12 h compared to Pre-Ex, and thereafter remained stable. This implies an increased oxygen pulse (VO2/HR) with approximately 10 % compared to Pre-Ex at the later half of the exercise. The cardiovascular drift did not progress continuously, but instead changed drastically when duration exceeded 6 hours. The changes in HR and VO2 might have different and complex explanations. HR drift might be explained mainly by central circulatory adaptation (e.g. desensitisation of cardiac adrenergic receptors) whereas drift in VO2 may depend upon peripheral changes (e.g. decreased mitochondrial efficiency). Consequently, using solely HR for determining exercise intensity and energy expenditure becomes invalid during ultra-endurance exercise, if the cardiovascular drift is not measured and taken into account.

 

Place, publisher, year, edition, pages
2008. 142- p.
National Category
Physiology
Identifiers
URN: urn:nbn:se:gih:diva-840ISBN: 9789727351565 (print)OAI: oai:DiVA.org:gih-840DiVA: diva2:174860
Projects
Physiology of Adenture Racing
Available from: 2009-02-26 Created: 2009-02-25 Last updated: 2017-03-31Bibliographically approved

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Mattsson, C. MikaelEnqvist, JonasEkblom, Björn
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