Blood flow regulation and oxygen uptake during high-intensity forearm exercise.

The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. We included 9 young (25 ± 2 yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. Blood flow was measured using Doppler-ultrasound, and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO2diff) during 6-min bouts of 60, 80, and 100% of maximal work rate (WRmax), respectively. Blood flow and oxygen uptake increased (P < 0.05) from 60%WRmax [557 ± 177(SD) ml/min; 56.0 ± 21.6 ml/min] to 80%WRmax (679 ± 190 ml/min; 70.6 ± 24.8 ml/min), but no change was seen from 80%WRmax to 100%WRmax Blood velocity (49.5 ± 11.5 to 58.1 ± 11.6 cm/s) and brachial diameter (0.49 ± 0.05 to 0.50 ± 0.06 cm) showed concomitant increases (P < 0.05) with blood flow from 60% to 80%WRmax, whereas no differences were observed in a-vO2diff Shear rate also increased (P < 0.05) from 60% (822 ± 196 s-1) to 80% (951 ± 234 s-1) of WRmax The mean response time (MRT) was slower (P < 0.05) for blood flow (60%WRmax 50 ± 22 s; 80%WRmax 51 ± 20 s; 100%WRmax 51 ± 23 s) than a-vO2diff (60%WRmax 29 ± 9 s; 80%WRmax 29 ± 5 s; 100%WRmax 20 ± 5 s), but not different from oxygen uptake (60%WRmax 44 ± 25 s; 80%WRmax 43 ± 14 s; 100%WRmax 41 ± 32 s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. In conclusion, when approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WRmax and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations.NEW & NOTEWORTHY This study evaluated blood flow regulation and oxygen uptake during small muscle mass forearm exercise with high to maximal intensity. Despite utilizing only a fraction of cardiac output, blood flow reached a plateau at 80% of maximal work rate and regulated peak oxygen uptake. Furthermore, the results revealed that muscle contractions dictated bulk oxygen delivery and yielded three times higher peak blood flow in the relaxation phase compared with mean values.

Pre-winter lipid stores in brown trout Salmo trutta along altitudinal and latitudinal gradients.

Pre-winter lipid stores of brown trout Salmo trutta L. parr were compared along altitudinal (0-920 m a.s.l.) and latitudinal (58-71° N) gradients. There were increases in lipid content (size adjusted to common lipid-free dry mass of 2·0 g, corresponding to fresh mass of 10 g) with both increasing altitude and latitude. Mean size-adjusted lipid content for S. trutta in high altitude rivers was 60% higher than at low altitude (0·29 and 0·18 g, respectively). Mean size-adjusted lipid content for S. trutta in northern rivers was 30% higher compared to that in southern rivers (0·30 and 0·23 g, respectively). There was a marked between-river variation in mean lipid storage, probably reflecting different strategies or opportunities for the pre-winter acquisition of lipid both locally within rivers and between different populations. This study shows that temperature or winter length, not latitudinal covariates such as annual light regime, governs lipid storage patterns in juvenile salmonids.

Morphological differences in parr of Atlantic salmon Salmo salar from three regions in Norway.

Morphological characters were compared in parr (total length 33-166 mm) of Atlantic salmon Salmo salar sampled from eight wild populations in three regions, three in northern, two in the middle and three in southern Norway, covering a distance of 1700 km (from 70° N to 58° N). On the basis of morphological characters 94·6% of the individuals were correctly classified into the three regions. Discrimination between populations within these three regions also had a high degree of correct classification (89·0-95·8%). Principle component analysis identified largest differences to be in head characters, notably eye diameter and jawbone, with the smallest diameter and head size among the northernmost populations. Fish from the southern rivers had a deeper body form whereas fish from the middle region had larger heads and pectoral fins. This illustrates that S. salar already in the early parr stage has morphological traits, which can be used in discrimination between regions and populations and that these differences are discernible in spite of the volume of escaped farmed fish spawning in Norwegian rivers during the past 30 years.

Pre-winter lipid stores in young-of-year Atlantic salmon along a north-south gradient.

The pre-winter lipid stores of young-of-the-year (YOY, age 0 year) Atlantic salmon Salmo salar were analysed along a north-south gradient from c. 71 to 58 degrees N, with winter conditions ranging from >200 days of ice cover to no ice. The rivers sampled in Northern Norway represent some of the most northerly S. salar rivers. There was an increase in lipid content with increasing latitude, and mean lipid content (size adjusted to common mass) for YOY in northern rivers were almost three times higher: 0.035 g compared to 0.013 g in southern rivers. The relationship was not sensitive to variation in sampling time or variation in YOY body size. The lipid stores, however, varied markedly between rivers and also between neighbouring rivers, indicating different strategies or opportunities for pre-winter lipid storage both at latitudinal and local scales.

Optical properties of the pineal window of Atlantic salmon (Salmo salar L.).

The spectral composition and intensity of light penetrating different parts of fresh preparations of the upper part of the skull of Atlantic salmon (Salmo salar) (fork length 25-30 cm) was investigated. All measurements were made in an aqueous medium, by moving the tip of an optical fibre in a three dimensional lattice below preparations that were illuminated by a parallel light source from above. The intensity of the transmitted light showed a well-defined maximum just below the pineal groove. Light that penetrated the skull from a source vertically above was refracted to produce a focusing point in the approximate position of the pineal body. Light projected from angles of 45° relative to the vertical position was only slightly (25%) attenuated, thus indicating a wide acceptance angle.There was an almost uniform transmission of light (of 3%) between 500 and 700 nm. The transmittance of UV light (350 nm) was about 10% of that of green light. These differences are small when compared with the intensity range reported for the pineal light receptors. The transmission properties are discussed in relation to the known diurnal changes in the spectral composition of natural light.