Increases in skin perfusion and blood oxygen in the non‐exercising human limbs during exercise in the heat: Implications for control of circulation

FIGURE 1. Schematic representation and image of the experimental protocol and an image depicting the experimental set‐up common to both studies. In both studies, the experimental trial consisted of three incremental cycle ergometer exercise tests of 3‐min stages at 20, 40, 60, 80 and 100% of W peak (322 ± 38 W). Between tests 1 and 2, participants completed 2 h of constant load (55% W peak, 177 ± 21 W) cycling exercise. All exercise tests were completed in a hot environment (35°C, 50% relative humidity, fan cooling).

FIGURE 2. Arterial (CaO2) and forearm venous (CfvO2) blood O2 content, and forearm skin a‐vO2 difference during repeated incremental (a, b) and constant, sub‐maximal (c, d) exercise in the heat. Values are means ± SD for nine participants. *Differences from rest, P <0.05; †differences from incremental tests 1 and 3, P <0.05.

FIGURE 3. Forearm blood flow, forearm skin blood flow, forearm tissue O2 saturation % and rectal temperature during repeated incremental (a–d) and constant, sub‐maximal (e–h) exercise in the heat. Values are means ± SD for nine participants. *Differences from rest, P <0.05; ‡differences from sub‐maximal (pooled average of 20% and 40% W peak values) exercise, P <0.05; †differences from tests 1 and 3, P <0.05.

FIGURE 4. Relationship between Q˙forearm and core temperature during the repeated incremental (a) and prolonged, constant submaximal (b) exercise in the heat, and in both exercise conditions collectively (c). Values are means ± SD for nine participants.

FIGURE 5. A comprehensive overview of blood oxygen saturation and the partial pressure of oxygen (PO2), in different vascular beds, collated from four studies, during incremental and constant, sub‐maximal exercise. Arterial, resting forearm, brain and exercising leg blood oxygen saturation during incremental (a, b) and constant, sub‐maximal (c, d) exercise in the heat. Arterial and resting forearm data are from study 1 as presented in the current paper. Brain O2 saturation and PO2 are redrawn from Trangmar et al. (2015, 2014). Exercising leg arterial and venous O2 saturation and PO2 are redrawn from González‐Alonso et al. (1998) and Trangmar et al. (2017). Arterial oxygen saturation decreases slightly from rest to peak exercise, whereas PO2 remains unchanged. Constant load submaximal exercise elicits little change in arterial oxygen saturation or PO2. Inactive‐forearm oxygen saturation and PO2, reflecting skin perfusion, are stable from rest to moderate intensity exercise, before increasing and stabilizing at a high level at near maximal exercise intensities. Comparatively, deep tissue (leg venous) oxygen saturation and PO2 decline substantially during both incremental and constant‐load…