Increased oxygenation in the non-contracting forearm muscle during contralateral skilful hand movement

What is the central question of this study? When performing skilful hand movement, motor command descends especially towards distal arm muscles. Does central command evoke a vascular response selectively in the distal arm muscles during skilful hand movement? What is the main finding and its importance? We found, using near-infrared spectroscopy, that unilateral skilful hand movement evoked a greater increase in oxygenation of the contralateral forearm muscle compared with that of the upper arm muscles. Mental imagery of the hand movement also increased oxygenation of the forearm muscle. These findings suggest that central command might contribute to the vasodilator response in the non-contracting forearm muscle during contralateral skilful hand movement.

The human hand is a special organ to perform skilful movement in daily life. To meet metabolic demands of the working distal arm muscles, central command might evoke neurogenic vasodilatation in the muscles. Based on our previous demonstration that a centrally generated vasodilator signal is transmitted bilaterally to skeletal muscles during exercise, centrally induced vasodilatation might occur in the non-contracting distal arm muscles during contralateral skilful hand movement. To examine this possibility, we used near-infrared spectroscopy to measure the relative concentrations of oxygenated haemoglobin (Oxy-Hb; as an index of regional blood flow) in the non-contracting arm muscles during skilful hand movement (two-ball rotation) in 22 subjects. Two-ball rotation increased Oxy-Hb of both forearm and upper arm muscles, with little changes in perfusion pressure and cardiac output. The increased Oxy-Hb was greater in the forearm muscle than in the upper arm muscles. The increased Oxy-Hb of the forearm muscle during two-ball rotation was greater than that during one-armed cranking performed with no load. Mental imagery of two-ball rotation increased Oxy-Hb of the forearm and biceps muscles. The increases in Oxy-Hb of both forearm and upper arm muscles during two-ball rotation were reduced by decreasing the level of task difficulty. Intravenous administration of atropine attenuated the increases in Oxy-Hb of the arm muscles during two-ball rotation. It is likely that contralateral skilful hand movement evokes a selective increase in Oxy-Hb of the non-contracting forearm muscle via a sympathetic cholinergic mechanism and that the increase in oxygenation might be mediated, at least in part, by central command.