Relative contraction force producing a reduction in calf blood flow by superimposing forearm exercise on lower leg exercise

Summary

The relative contraction force producing a reduction in exercise hyperaemia was studied by superimposing handgrip contraction at different intensities on plantar flexion of low intensity. Ten active women served as subjects. Blood flow to the forearm ($\dot Q$ _forearm) and calf ($\dot Q$ _calf) was measured with mercury-in-rubber strain gauges by venous occlusion plethysmography immediately after 60 s of rhythmic plantar flexion at 10% of maximum voluntary contraction (MVC), which was expressed as P₁₀H₀, or combined plantar flexion and handgrip contraction. In the combined exercise, handgrip exercise at 30%, 50% or 70% MVC was added to plantar flexion during the last 30 s of exercise (P₁₀H₃₀, P₁₀H₅₀ and P₁₀H₇₀, respectively). The $\dot Q$ _forearm increases after P₁₀H₃₀, P₁₀H₅₀ and P₁₀ were significantly larger (P<0.01) than that after P₁₀H₀, and the difference between P₁₀H₃₀and P₁₀H₇₀ was also significant (P<0.01) Immediate post-exercise $\dot Q$ _calf after P₁₀H₀ increased by 7.4 (SEM 0.9) ml·100 ml⁻¹·min⁻¹. When handgrip contraction at 70% MVC was added, the $\dot Q$ _calf increase after exercise [4.5 (SEM 0.7) ml·100 ml⁻¹·min⁻¹] was significantly lower than after plantar flexion alone (P<0.05). However, no significant change was found in $\dot Q$ _calf when the forces of added handgrip contraction were 30% and 50% MVC, although the mean value of $\dot Q$ _calf increase was lower after P₁₀H₅₀ combined exercise. Calf vascular resistance calculated as $\overline {BP}$/$\dot Q$ _calf ($\overline {BP}$ mean blood pressure) tended to increase after P₁₀H₇₀ to a nonsignificant extent. Heart rate and oxygen uptake in these exercises increased when handgrip contraction at 30%, 50%, or 70% MVC was added to plantar flexion at 10% MVC. However, the increases were considerably lower than the maximal ones. Thus, a reduction of $\dot Q$ _calf occurred even when the cardiac demand from the muscle was below its maximum. In conclusion, post-exercise hyperaemia in the active limb working at low intensity was inhibited by superimposition of exercise of another limb at a high contraction force. The critical force producing attenuation of exercise hyperaemia after combined exercise of short duration was found to be higher than 50% MVC in the case of handgrip contraction plus plantar flexion.