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Oxygen transport during exercise in human subjects.

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    ABSTRACT: Cross-country skiing is one of the most demanding endurance sports. It im-poses extensive physiological challenges due to the perpetual changes be-tween, and utilisation of, different skiing techniques, each involving the upper and lower body to various extents. Altogether, the uniqueness of the sport has over the years contributed to significant interest from physiologists in their ongoing ambition to understand more about the human engine. Oxygen uptake Hill and his colleagues were pioneers in the discussion of the major links in the chain for transport of oxygen in humans, discussing potential limiting factors (Hill et al., 1924). Since then, several studies have reported improvement in maximal oxygen uptake (VO2 max) after endurance training (for refs see Mitchell & Saltin, 2003). Several factors contributes to this increase; 1) an increased cardiac output, 2) an optimal distribution of the blood to the most active muscles and minimising the blood flow to the non-active tissues and organs, and 3) greater extraction of the delivered oxygen. It has been pro-posed that maximal oxygen uptake is not limited by one specific link, rather it is determined by a close integrated interaction between all the links in the oxy-gen transport chain (Di Prampero, 1985; Wagner et al., 1997). Among these, the capacity of the cardiovascular system to deliver oxygen to the skeletal muscles, i.e. cardiac output and blood flow, is considered to be the most im-portant limiting factor (Mitchell et al., 1958; Ekblom & Hermansen, 1968; Di Prampero, 1985; Saltin & Strange, 1992). Numerous studies have documented that successful cross-country skiers have exceptionally high aerobic power, both in absolute and relative values (Strømme et al., 1977; Rusko, 1992; Holmberg et al., 2007). Few male skiers have won medals in a major championship without having maximal oxygen
    Science and Skiing IV, Edited by Erich (EDT) Mueller, Stefan (EDT) Lindinger, Thomas (EDT) Stogg, 01/2009: chapter The competitive Cross-Country Skier - an impressive human engine: pages 101-109; Meyer Meyer Sport (UK) Ltd., ISBN: 9781841262550
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    ABSTRACT: Physical activity is essential in obesity management, but exercise capacity is compromised in obese individuals due to the excessive body mass, impacting on body movement's energetics, and to the dysfunctions of regulatory mechanisms, affecting cardiovascular responses. This study aims to compare the energetics and cardiovascular responses of walking and cycling in obese women, and to formulate recommendations regarding the most suitable type of exercise for obesity. Fifteen obese (OB) and six normal weight (NW) women exercised on treadmill (TM) and cycle ergometer (CE). During both exercise modalities, metabolic rate was higher in OB than in NW and correlated with measures of body mass. Leg movement metabolic rate during cycling depended upon individual adiposity, and when accounted for, mechanical efficiency was similar in the two groups. When accounting for extra mass, differences in metabolic rate among groups are abolished for CE, indicating no obesity impairment of muscle efficiency, but not for TM, suggesting that differences in biomechanics may explain the higher net cost of transport of OB. In both groups, HR was higher during CE than TM at the same oxygen uptake (VO(2)), but in OB the HR increment over VO(2) was greater for CE than for TM. Therefore, due to different cardiovascular responses to TM and CE in OB, walking is more convenient, enabling OB to attain target energy expenditure at lower HR or in a shorter time.
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    ABSTRACT: An acute reduction of blood hemoglobin concentration ([Hb]), even when the circulating blood volume is maintained, results in lower (.)V(O(2)(max) and endurance performance, due to the reduction of the oxygen carrying capacity of blood. Conversely, an increase of [Hb] is associated with enhanced (.)V(O(2)(max) and endurance capacity, that is also proportional to the increase in the oxygen carrying capacity of blood. The effects on endurance capacity appear more pronounced and prolonged than on (.)V(O(2)(max). During submaximal exercise, there is a tight coupling between O(2) demand and O(2) delivery, such that if [Hb] is acutely decreased muscle blood flow is increased proportionally and vice versa. During maximal exercise with either a small or a large muscle mass, neither peak cardiac output nor peak leg blood flow are affected by reduced [Hb]. An acute increase of [Hb] has no effect on maximal exercise capacity or (.)V(O(2)(max) during exercise in acute hypoxia. Likewise, reducing [Hb] in altitude-acclimatized humans to pre-acclimatization values has no effect on (.)V(O(2)(max) during exercise in hypoxia.
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