[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) concentration in exhaled gas is a marker of some inflammatory processes in the lung, and endogenous NO plays a role in the physiological responses to exercise and altitude. The aim of this study was to compare changes in exhaled NO concentration 5-60 mins after high-intensity exercise at 2800 m and at 180 m altitude.
Twenty trained healthy volunteers (12 men), aged 19-28 years, were included in this open, crossover study. Subjects performed two exercise tests at different altitudes, 2800 m and 180 m, in a randomized order. The fraction of NO in exhaled gas (FENO ) was measured 5 mins before and 5-60 mins after 8 mins of running on a treadmill at a heart rate (HR) of 90% of peak HR. Peak HR was assessed during a pretest at 180 m. Ambient temperature was 20·1°C (SD = 1·2) and relative humidity 40·2% (SD = 3·2). FENO measurements were corrected for altitude gas density effects and converted to partial pressure of NO (PENOcorr ).
PENOcorr was reduced from 1·47 (1·21, 1·73) millipascal (mPa) at baseline to 1·11 (0·87, 1·34) mPa 5 mins after exercise at 2800 m and from 1·54 (1·24, 1·84) to 1·04 (0·87, 1·22) mPa 5 mins after exercise at 180 m. There was no difference in PENOcorr between exercise at 2800 m and 180 m, and PENOcorr was normalized within 20 mins.
Exercise at 2800 m induces a similar acute reduction in exhaled nitric oxide concentration as compared with 180 m in healthy subjects.
Clinical Physiology and Functional Imaging 01/2014; · 1.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Post-exercise muscle glycogen repletion after a glucose infusion was studied in diabetic (D) and non-diabetic (ND) subjects in two series of experiments; one in which muscle biopsies were examined and another in which arterial-femoral vein (a-fv) glucose differences were investigated. The results were compared with a control experiment where the subjects rested before the infusion. All experiments were performed after 12-14 h fast. The diabetics had not taken their morning insulin. The subjects bicycled till exhaustion. 15 min after cessation of exercise 0.5 g glucose per kg body weight was infused. Blood samples were drawn before exercise, in the last minute of exercise and repetetively during recovery. Biopsies were obtained before exercise, immediately after exercise and 65 min after the infusion. During exercise muscle glycogen content decreased from 68.7 ± 5.0 (D) and 81.4 ± 8.6 (ND) to 33.9 ± 5.1 (D) and 21.6 ± 3.3 (ND) mmol glucosyl units/kg w.w. After the glucose infusion muscle glycogen increased to 44.2 ± 3.8 (D) (P < 0.005) and 35.8 ± 5.7 (ND) (P < 0.005) mmol glucosyl units/kg w.w. Glycogen synthesis rates during recovery were 9.6 ± 1.5 (D) and 13.6 ± 2.6 (ND) mmol glucosyl units/kg w.w. per hr. No significant differences were observed in glycogen content or glycogen synthesis rate between the two groups. In the control experiments, no increase in muscle glycogen content was observed. The post-infusion a-fv-glucose differences were similar in diabetic and non-diabetic subjects during recovery, and in both groups larger than in the control experiments. It is concluded that during recovery after exercise a major portion of glucose infused as a single injection 15 min after exercise in diabetic and non-diabetic subjects, is utilized by muscle; mainly for glycogen synthesis. The rate of glycogen synthesis is similar in both groups. When glucose is infused without previous exercise, no changes in muscle glycogen content is observed.
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