The blood flow through the "resting" arm during hand-grip contractions.

These experiments were designed to add information about the control of the circulation in the contralateral arm during isometric hand-grip contractions. The existing evidence came from two laboratories and was in conflict. The most recent data claimed that there is an inevitable increase in blood flow through the contralateral arm and that it is neurogenically controlled, while some degree of electromyographic activity was not associated with an increase in the blood flow. In the present experiments, the blood flow and the oxygen uptake over the arm were first "calibrated" against the electromyographic activity during isometric contractions at known low tensions. In steady state conditions, there were direct, linear relationships between all four measurements. The "calibrated" arm then became the contralateral (resting) arm, while strong isometric contractions were held by the other hand. Of 12 subjects examined, half showed no increase in blood flow or electromyographic activity. The other six subjects all showed some muscular activity (electromyogram) in the contralateral arm which was always associated with an increase in blood flow and oxygen uptake. Not all those findings fitted the "calibration" closely; the problems of this approach are discussed.