Effects of skeletal muscle fiber deformation on lymphatic volumes

Because lymphatics in skeletal muscle have no smooth muscle, they are expanded and compressed solely by stresses in the surrounding tissue. Whole organ experiments have indicated that lymph flow is significantly elevated during muscle activity, yet the underlying mechanism for lymph formation has not been identified. To investigate this mechanism, specimens of the rat spinotrapezius muscle were fixed in situ at the undeformed in vivo length, and also in the stretched and contracted states, for histological examination. Cross-sectional areas of lymphatic vessels, skeletal muscle fibers, blood vessels, and interstitial space were measured using a stereological technique. The in situ preparation with intact muscle fascia was essential for preservation of interstitial volume. The lymphatic cross-sectional areas and muscle stretch ratios from 20 rats showed that lymphatic volume increased by 57% for a 20% stretch, and decreased by 45% for a 20% contraction. Deformation of the incompressible muscle fibers appears to inversely affect surrounding tissue structures; e.g., decreased fiber cross-sectional area during stretch increases interstitial spacing between fibers, which in turn expands lymphatics.