| 1. |
- Calbet, J, et al.
(författare)
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Maximal vascular conductances during whole body upright exercise in humans
- 2004
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Ingår i: The Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 558:1, s. 319-331
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Tidskriftsartikel (refereegranskat)abstract
- That muscular blood flow may reach 2.5 l kg�1 min�1 in the quadriceps muscle has led to the suggestion that muscular vascular conductance must be restrained during whole body exercise to avoid hypotension. The main aim of this study was to determine the maximal arm and leg muscle vascular conductances (VC) during leg and arm exercise, to find out if the maximal muscular vasodilatory response is restrained during maximal combined arm and leg exercise. If during maximal exercise arms and legs had been vasodilated to the observed maximal levels then mean arterial pressure would have dropped at least to 75�77 mmHg in our experimental conditions. It is concluded that skeletal muscle vascular conductance is restrained during whole body exercise in the upright position to avoid hypotension. AVKORTAT ABSTRACT
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| 2. |
- Calbet, J, et al.
(författare)
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Why do the arms extract less oxygen than the legs during exercise?
- 2005
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 289, s. 1448-1458
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Tidskriftsartikel (refereegranskat)abstract
- To determine whether conditions for O2 utilization and O2 off-loading from the hemoglobin are different in exercising arms and legs, six cross-country skiers participated in this study. Femoral and subclavian vein blood flow and gases were determined during skiing on a treadmill at 76% maximal O2 uptake (O2 max) and at O2 max with different techniques: diagonal stride (combined arm and leg exercise), double poling (predominantly arm exercise), and leg skiing (predominantly leg exercise). The percentage of O2 extraction was always higher for the legs than for the arms. At maximal exercise (diagonal stride), the corresponding mean values were 93 and 85% (n = 3; P < 0.05). During exercise, mean arm O2 extraction correlated with the PO2 value that causes hemoglobin to be 50% saturated (P50: r = 0.93, P < 0.05), but for a given value of P50, O2 extraction was always higher in the legs than in the arms. Mean capillary muscle O2 conductance of the arm during double poling was 14.5 (SD 2.6) ml·min–1·mmHg–1, and mean capillary PO2 was 47.7 (SD 2.6) mmHg. Corresponding values for the legs during maximal exercise were 48.3 (SD 13.0) ml·min–1·mmHg–1 and 33.8 (SD 2.6) mmHg, respectively. Because conditions for O2 off-loading from the hemoglobin are similar in leg and arm muscles, the observed differences in maximal arm and leg O2 extraction should be attributed to other factors, such as a higher heterogeneity in blood flow distribution, shorter mean transit time, smaller diffusing area, and larger diffusing distance, in arms than in legs. diffusing capacity; fatigue; oxygen extraction; performance; training
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| 3. |
- Van Hall, G, et al.
(författare)
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Leg and arm lactate and substrate kinetics during exercise
- 2003
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 284:1, s. E193-E205
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Tidskriftsartikel (refereegranskat)abstract
- To study the role of muscle mass and muscle activity on lactate and energy kinetics during exercise, whole body and limb lactate, glucose, and fatty acid fluxes were determined in six elite cross-country skiers during roller-skiing for 40 min with the diagonal stride (Continuous Arm + Leg) followed by 10 min of double poling and diagonal stride at 72-76% maximal O(2) uptake. A high lactate appearance rate (R(a), 184 +/- 17 micromol x kg(-1) x min(-1)) but a low arterial lactate concentration ( approximately 2.5 mmol/l) were observed during Continuous Arm + Leg despite a substantial net lactate release by the arm of approximately 2.1 mmol/min, which was balanced by a similar net lactate uptake by the leg. Whole body and limb lactate oxidation during Continuous Arm + Leg was approximately 45% at rest and approximately 95% of disappearance rate and limb lactate uptake, respectively. Limb lactate kinetics changed multiple times when exercise mode was changed. Whole body glucose and glycerol turnover was unchanged during the different skiing modes; however, limb net glucose uptake changed severalfold. In conclusion, the arterial lactate concentration can be maintained at a relatively low level despite high lactate R(a) during exercise with a large muscle mass because of the large capacity of active skeletal muscle to take up lactate, which is tightly correlated with lactate delivery. The limb lactate uptake during exercise is oxidized at rates far above resting oxygen consumption, implying that lactate uptake and subsequent oxidation are also dependent on an elevated metabolic rate. The relative contribution of whole body and limb lactate oxidation is between 20 and 30% of total carbohydrate oxidation at rest and during exercise under the various conditions. Skeletal muscle can change its limb net glucose uptake severalfold within minutes, causing a redistribution of the available glucose because whole body glucose turnover was unchanged.
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| 4. |
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| 5. |
- Nilsson, Johnny, 1950-, et al.
(författare)
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Contribution of leg muscle forces to paddle force and kayak speed during maximal effort flat-water paddling
- 2016
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Ingår i: International Journal of Sports Physiology and Performance. - : Human Kinetics. - 1555-0265 .- 1555-0273. ; 11:1, s. 22-27
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to investigate the contribution of leg-muscle-generated forces to paddle force and kayak speed during maximal-effort flat-water paddling. Five elite male kayakers at national and international level participated. The participants warmed up at progressively increasing speeds and then performed a maximal-effort, nonrestricted paddling sequence. This was followed after 5 min rest by a maximal-effort paddling sequence with the leg action restricted—the knee joints “locked.” Left- and right-side foot-bar and paddle forces were recorded with specially designed force devices. In addition, knee angular displacement of the right and left knees was recorded with electrogoniometric technique, and the kayak speed was calculated from GPS signals sampled at 5 Hz. The results showed that reduction in both push and pull foot-bar forces resulted in a reduction of 21% and 16% in mean paddle-stroke force and mean kayak speed, respectively. Thus, the contribution of foot-bar force from lower-limb action significantly contributes to kayakers’ paddling performance.
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| 6. |
- Nilsson, Johnny E, et al.
(författare)
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New Devices for Measuring Forces on the Kayak Foot-Bar and on the Seat During Flat-Water Kayak Paddling : a technical report.
- 2014
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Ingår i: International Journal of Sports Physiology and Performance. - : Human Kinetics. - 1555-0265 .- 1555-0273. ; 9:2, s. 365-70
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to develop and validate portable force-measurement devices for recordings of push and pull forces applied by each foot to the foot-bar of a kayak, and the horizontal force at the seat. A foot-plate on a single-point force transducer mounted on the kayak foot-bar underneath each foot allowed the push and pull forces to be recorded. Two metal frames interconnected with four linear ball-bearings and a force transducer allowed recording of horizontal seat force. The foot-bar force device was calibrated by loading each foot plate with weights in the push pull direction perpendicular to the foot plate surface while the seat force device was calibrated to horizontal forces with and without weights on the seat. A strong linearity (r2=0.99-1.0) was found between transducer output signal and load force in the push and pull directions for both foot-bar transducers perpendicular to the foot plate and the seat-force measuring device. Reliability of both devices was tested by means of a test-retest design. The coefficient of variation (CV) for foot-bar push and pull forces ranged from 0.1 to 1.1% and the CV for the seat forces varied between 0.6 - 2.2%. The present study opens up for new investigations of the forces generated within the kayak and ways to optimize kayak paddling performance.
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| 7. |
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