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-vO) during 6-min bouts of 60, 80, and 100% of maximal work rate (WR), respectively. Blood flow and oxygen uptake increased ( < 0.05) from 60%WR [557 ± 177(SD) ml/min; 56.0 ± 21.6 ml/min] to 80%WR (679 ± 190 ml/min; 70.6 ± 24.8 ml/min), but no change was seen from 80%WR to 100%WR 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 ( < 0.05) with blood flow from 60% to 80%WR whereas no differences were observed in a-vO Shear rate also increased ( < 0.05) from 60% (822 ± 196 s) to 80% (951 ± 234 s) of WR The mean response time (MRT) was slower ( < 0.05) for blood flow (60%WR 50 ± 22 s; 80%WR 51 ± 20 s; 100%WR 51 ± 23 s) than a-vO (60%WR 29 ± 9 s; 80%WR 29 ± 5 s; 100%WR 20 ± 5 s), but not different from oxygen uptake (60%WR 44 ± 25 s; 80%WR 43 ± 14 s; 100%WR 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 WR 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. 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.

Maximal strength training-induced improvements in forearm work efficiency are associated with reduced blood flow

“…The subject then performed rhythmic work for 6 min, and work efficiency data were collected within the final minute of this exercise period. In combination, a prior study (36) and a pilot study showed that blood gas and forearm blood flow measurements reached a plateau, defined as no change in V O2 over time (3), the final 2-3 min of the test. Position, contraction range of motion, and frequency were identical to that of the WR max test.…”

“…Although a-vO 2diff was calculated indirectly from pulmonary V O 2 , the proposal may be reasonable as several differences in vascular and metabolic responses exist between arm and leg exercise (8,9,35). A pivotal impediment in arms (36,44) compared with legs is the larger influence from muscle contractions, resulting in a substantial hindrance to blood flow. This may be decisive for blood flow as an adapting mechanism in arms, and a-vO 2diff may thus be the regulated component in the oxygen supply and demand interplay after arm MST.…”

Shear‐thinning behaviour of blood in response to active hyperaemia: Implications for the assessment of arterial shear stress‐mediated dilatation

“…The coefficient of variation (CV) for the blood viscosity duplicates was <4%; the CV values did not vary according to the specific shear rate. The shear rates selected are within the physiological range documented for the brachial artery in humans at rest and during rhythmic handgrip exercise, based on pilot testing in our laboratory and previous literature using a similar exercise protocol (Nyberg et al., ). All blood viscosity measurements were performed at a standardized temperature of 37°C with the use of a circulating heated water bath.…”

“…To this end, we used high‐resolution Duplex ultrasound and serial venous blood samples draining the forearm for the assessment of brachial artery shear rate and blood viscosity, respectively. We measured blood viscosity in vitro across 10 discrete shear rates (75–1500 s −1 ) spanning the physiological range documented for the brachial artery in basal and exercise conditions (Nyberg, Berg, Helgerud, & Wang, ). Subsequently, we modelled the non‐Newtonian behaviour of blood via a two‐phase exponential decay to obtain a direct estimate of the viscosity corresponding to the ultrasound‐derived brachial artery shear rate to evaluate the shear stress response.…”

Dynamics of skeletal muscle blood flow and vasodilation with age

“…Blood flow during rhythmic exercise is bi-phasic in nature, plateauing (e.g. steady-state) within a few minutes of the onset of exercise (212,242,251,252,(267)(268)(269). The kinetic response of blood flow and vasodilation may be separated into three distinct phases.…”