Peripheral Limitations to Oxygen Transport in Forearm
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Maximal oxygen consumption (VO2max) is concidered being the factor contributing most to aerobic endurance and to have an important role concidering both health and quality of life. The ongoing discussion the last decades has been whether VO2max is limited primarily of central factors (cardiacoutput) or by peripheral factors (arteriovenous difference). If investigating the peripheral factors using small muscle mass, the heart is able to deliver a large enough blood flow to satisfy the needfor oxygen, and the cardiac output will not be limiting for VO2max. Then, the limitations to VO2max are in the arteriovenous difference, making it possible to study whether it differs between individuals. In situations using a limited muscle mass the highest rate that oxygen can be taken up is referred to as peak oxygen consumption (VO2peak). There has been shown higher arteriovenous difference in trained leg compared to untrained leg. Our intention was to examine if this difference also can be measured in upper extremities, in forearm. The forearm muscle is highly suitable for studying arteriovenous difference, because it represents even a smaller amount of muscle than legmuscle, and therefore will stress the cardiac output even less. Even when using only one leg formaximal work, oxygen consumption is approximately 50% limited by cardiac output. We recruited15 subjects. Eight of them had trained forearms, being climbers participating in competitions on national and international level, seven had untrained forearms. The testing was done with a handgrip dynanometer, training at maximum aerobic intensity for three minutes. The last 20 seconds of the training, a blood sample was taken with a catheter in v. basilica and the sample was analyzed for oxygen. There was a significant difference in arteriovenous difference between restand maximal work within the groups, but in contrast to our hypothesis, we did not find a difference in arteriovenous difference between the two groups at maximal intensity. When it comes to peripheral limitations to VO2peak, the differences between trained and untrained therefore likely lies in blood flow, not in the arteriovenous difference.