Slow volume changes in calf and thigh during cycle ergometer exercise

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Abstract
To study the transcapillary fluid movements in the human lower limb in the upright body position and during muscle exercise, the slow changes in thigh and calf volumes were measured by mercury-in-rubber-strain gauge plethysmography. Measurements were carried out on 20 healthy volunteers while sitting, standing and doing cycle ergometer exercise at intensities of 50 and 100-W. A plethysmographic recording of slow extravascular volume changes during muscle exercise was possible because movement artefacts were eliminated by low-pass filtering. While standing and sitting the volumes of both thigh and calf increased due to enhanced transcapillary filtration. While standing the mean rate of increase was 0.13%·min−1 in the calf and 0.09%·min−1 in the thigh. During cycle ergometer exercise at 50 and 100 W, the calf volume decreased with a mean rate of −0.09%·min−1. In contrast, the thigh volume did not change significantly during exercise at 50 W and increased at 100 W. Most of the increase occured during the first half of the experimental period i.e. between min 2 and 12, amounting to +0.6%. Thus, simultaneous measurements revealed opposite changes in the thigh and calf. This demonstrates that the conflicting findings reported in the literature may have occured because opposite changes can occur in different muscle groups of the working limb at the same time. Lowered venous pressure, increased lymph flow and increased tissue pressure in the contracting muscle are considered to have caused the reduction in calf volume during exercise. In accordance with the literature the increases in thigh volume are explained as a result of the enhanced metabolism of the thigh muscles, which do most of the work during cycling: increased metabolism led to local hyperosmolality, which in turn caused an osmotic transcapillary fluid shift into the extravascular space. To some extent an enhanced transcapillary filtration associated with the exercise hyperaemia, might have made a additional contribution to the fluid accumulation.

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