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Long-chain fatty acids (LCFA) are important sources of energy in contracting skeletal muscle: during the course of endurance exercise the contribution of LCFA in energy metabolism increases whereas when the intensity of exercise increases, the energy need is covered more and more by carbohydrates. Although this has been known for nearly 100 years, the mechanisms controlling fatty acid uptake and oxidation during various exercise modes are still not completely elucidated. Besides passive diffusion, data suggest that both membrane-associated and cytosolic fatty acid binding proteins are involved in the uptake of LCFA into skeletal muscle. However, data from human studies suggest that the regulation of fatty acid utilization in skeletal muscle during exercise lies mainly within the entrance into the mitochondria or metabolism within the mitochondria. Although possible compartmentalization within the cell makes definitive conclusions difficult, available evidence suggests that changes in malonyl CoA concentration in muscle do not play a major regulatory role in controlling LCFA oxidation during exercise in man. In contrast, it is suggested that the availability of free carnitine may play a major regulatory role in oxidation of LCFA during exercise.

We examined the influence of hyperoxia on peak oxygen uptake (Vo 2peak ) and peripheral gas exchange during exercise with the quadriceps femoris muscle. Young, trained men In = 5) and women (n = 3) performed single-leg knee-extension exercise at 70% and 100% of maximum while inspiring normal air (NOX) or 60% O 2 (HIOX). Blood was sampled from the femoral vein of the exercising limb and from the contralateral artery. In comparison with NOX, hyperoxic arterial O 2 tension (P a o 2 ) increased from 13.5 ± 0.3 (x ± SE) to 41.6 ± 0.3 kPa, O 2 saturation (S a O 2 ) from 98 ± 0.1 to 100 ± 0.1%, and O 2 concentration (C a O 2 ) from 177 ± 4 to 186 ± 4 mL L -1 (all P < 0.01). Peak exercise femoral venous Po 2 (P v o 2 ) was also higher in HiOX (3.68 ± 0.06 vs. 3.39 ± 0.7 kPa; P < 0.05), indicating a higher O 2 diffusion driving pressure. HiOX femoral venous O 2 saturation averaged 36.8 ± 2.0% as opposed to 33.4 ± 1.5% in NOX (P < 0.05) and O 2 concentration 63 ± 6 vs. 55 ± 4 mL L -1 (P < 0.05). Peak exercise quadriceps blood flow (Q leg ), measured by the thermodilution technique, was lower in HiOX than in NOX, 6.4 ± 0.5 vs. 7.3 ± 0.9 L min -1 (P < 0.05); mean arterial blood pressure at inguinal height was similar in NOX and HiOX at 144 and 142 mmHg, respectively. O 2 delivery to the limb (O leq times C a O 2 ) was not significantly different in HiOX and NOX. Vo 2peak of the exercising limb averaged 890 mL min -1 in NOX and 801 mL min -1 in HiOX (n.s.) corresponding to 365 and 330 mL min -1 per kg active muscle, respectively. The Vo 2peak -to-P v o 2 ratio was lower (P < 0.05) in HiOX than in NOX suggesting a lower O 2 conductance. We conclude that the similar Vo 2peak values despite higher O 2 driving pressure in HiOX indicates a peripheral limitation for Vo 2peak . This may relate to saturation of the rate of O 2 turnover in the mitochondria during exercise with a small muscle group but can also be caused by tissue diffusion limitation related to lower O 2 conductance.

Controversy exists whether recruitment of a large muscle mass in dynamic exercise may outstrip the pumping capacity of the heart and require neurogenic vasoconstriction in exercising muscle to prevent a fall in arterial blood pressure. To elucidate this question, seven healthy young men cycled for 70 minutes at a work load of 55-60% VO2max. At 30 to 50 minutes, arm cranking was added and total work load increased to (mean +/- SE) 82 +/- 4% of VO2max. During leg exercise, leg blood flow average 6.15 +/- .511 minutes-1, mean arterial blood pressure 137 +/- 4 mmHg and leg conductance 42.3 +/- 2.2 ml minutes-1 mmHg-1. When arm cranking was added to leg cycling, leg blood flow did not change significantly, mean arterial blood pressure increased transiently to 147 +/- 5 mmHg and leg vascular conductance decreased transiently to 33.5 +/- 3.1 ml minutes-1 mmHg-1. Furthermore, arm cranking doubled leg noradrenaline spillover. When arm cranking was discontinued and leg cycling continued, leg blood flow was unchanged but mean arterial blood pressure decreased to values significantly below those measured in the first leg exercise period. Furthermore, leg vascular conductance increased transiently, and noradrenaline spillover decreased towards values measured during the first leg exercise period. It is concluded that addition of arm cranking to leg cycling increases leg noradrenaline spillover and decreases leg vascular conductance but leg blood flow remains unchanged because of a simultaneous increase in mean arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Aim: It is not clear how lipolysis changes in skeletal muscle and adipose tissue during exercise of different intensities. We aimed at estimating this by microdialysis and muscle biopsy techniques. Methods: Nine healthy, young men were kicking with both legs at 25% of maximal power (Wmax) for 45 min and then simultaneously with one leg at 65% and the other leg at 85%Wmax for 35 min. Results: Glycerol concentrations in skeletal muscle and adipose tissue interstitial fluid and in arterial plasma increased (P

The temporal changes in muscular blood flow and in the release of ions and metabolites have been studied during and after short-lasting isometric contractions Blood velocities in the human femoral artery were measured using pulsed bidirectional Doppler ultrasound equipment during single contractions of the quadriceps muscle group. Contractions of 5 s and 30 s duration and at a tension of 10% MVC (maximal voluntary contraction) were investigated. Even the contractions of 5 s duration caused conspicuous post-contraction increases in femoral arterial flow. . The following substances were analysed in the femoral vein during and following the contractions: potassium, lactate, inorganic phosphate, calcium, sodium, oxygen and haemoglobin. Following contractions of 5 s duration, an increase in the venous potassium concentration (by 0.9mM) was found, but there was no change in concentration of any of the other substances analysed. Following contractions of 30 s duration a more marked increase in the venous potassium concentration (by 1.5 mM) was found, and in addition substantial changes in venous lactate concentration and oxygen saturation. There were small but statistically significant changes in the concentrations of inorganic phosphate and calcium, but no change in the sodium concentration. The time-course and magnitude of the changes in venous potassium concentration fit well with the idea that potassium is important in the initiation and regulation of the functional hyperaemia in contracting muscles.

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one-legged knee-extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for 10 min at each of 50% and 100% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (NAe) or of adrenalin (Ae) is required: NAe was measured by repeating the experiment under constant [3H]NA infusion following a 40-min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this tissue.

Seven men performed one-legged isometric knee-extension at 5% MVC for 1 h. Intramuscular pressure increased with contraction from its resting value of 14 (2-31) mmHg. Some intramuscular pressure recordings stayed at an almost constant level through the 1 h contraction, but most recordings showed large fluctuations from resting values up to 90 mmHg. The overall mean intramuscular pressure was twice the resting value. In some cases, EMG recordings confirmed that the changes in intramuscular pressure were related to alternating recruitment of various parts of the knee-extensors. Blood flow in the femoral vein increased within 3 min of 5% MVC to a level of 1.58 (1.25-2.22) 1 min-1 and no significant changes occurred during the 1 h contraction. In two subjects blood flow was measured also in the recovery period, and this decreased almost immediately when the muscle relaxed. It is concluded that during low-level static contractions, the blood supply to the exercising muscle is maintained at a sufficiently high level, and that the alternating recruitment of muscle fibres may result in a heterogeneously distributed blood flow within the contracting muscle. Despite this the muscle was fatigued after the 1 h at 5% MVC. The rating of perceived exertion (RPE) increased from 1.9 (1-3) at the beginning to 4.5 (2-8) at the end of contraction, and MVC was decreased by 12% after the contraction.