title: Blood flow regulation and oxygen uptake during high-intensity forearm exercise.
abstract: 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%WRmaxto 100%WRmaxBlood 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-vO2diffShear rate also increased (P< 0.05) from 60% (822 ± 196 s-1) to 80% (951 ± 234 s-1) of WRmaxThe mean response time (MRT) was slower (P< 0.05) for blood flow (60%WRmax50 ± 22 s; 80%WRmax51 ± 20 s; 100%WRmax51 ± 23 s) than a-vO2diff(60%WRmax29 ± 9 s; 80%WRmax29 ± 5 s; 100%WRmax20 ± 5 s), but not different from oxygen uptake (60%WRmax44 ± 25 s; 80%WRmax43 ± 14 s; 100%WRmax41 ± 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 WRmaxand 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 & NOTEWORTHYThis 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.
authors.affiliation: Department of Circulation and Medical Imaging, Faculty of Medicine, the Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: S K
authors.initials: SK
authors.lastname: Nyberg
authors.affiliation: Faculty of Health and Social Sciences, Molde University College, Molde, Norway.
authors.forename: O K
authors.initials: OK
authors.lastname: Berg
authors.affiliation: Department of Circulation and Medical Imaging, Faculty of Medicine, the Norwegian University of Science and Technology, Trondheim, Norway.|Hokksund Medical Rehabilitation Centre, Hokksund, Norway.|Department of Sports and Outdoor Life Studies, Telemark University College, Bø, Norway.
authors.forename: J
authors.initials: J
authors.lastname: Helgerud
authors.affiliation: Department of Circulation and Medical Imaging, Faculty of Medicine, the Norwegian University of Science and Technology, Trondheim, Norway; eivind.wang@ntnu.no.|Department of Medicine, University of Utah, Salt Lake City, Utah; and.|Department of Research and Development, St. Olav's University Hospital, Trondheim, Norway.
authors.forename: E
authors.initials: E
authors.lastname: Wang
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005542:Forearm / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: V̇o2 kinetics; hemodynamics; oxygen extraction; shear stress; small muscle mass; vascular conductance