Six male subjects within the age range of 20–35 yr consented to perform static calf muscle contractions at 7.5, 15, and 30% of their maximum voluntary contractile strength (MVC) for a period of 2 min each. Isometric contractions were performed in a sitting position by pressing the knee against a solid support plate via plantar flexion. Calf muscle blood flow (BF) was measured periodically before, during, and after each contraction by a Whitney gauge. Average resting BF was 3.9 ml . min-1 . 100 ml-1 of calf volume. During the 7.5, 15, and 30% MVC contractions, BF increased to steady-state levels of 7.2, 7.9, and 5.3 ml . min-1 . 100 ml-1, respectively. The values for 7.5 and 15% MVC were significantly higher than resting BF (P less than or equal to 0.05). The postcontraction hyperemia, measured as the area under the postcontraction BF curve, averaged 4.4, 10.1, and 23.2 ml/100 ml, respectively, for the 7.5, 15, and 30% MVC efforts. Comparison of these values with corresponding hyperemic volumes during contraction showed that the portions of the total BF response that occurred in the postcontraction periods were 41, 57, and 88%, respectively, for the 7.5, 15, and 30% efforts. These results demonstrate that during static calf muscle contractions BF increases by only a modest amount, and at even small forces of contraction a sizable portion of the total flow response occurs in the postcontraction period.
Resting load regulates intracellular Ca2+-force relationship in bovine vascular smooth muscle.
