Metabolic cost of postural actions during iso- and antidirectionally coupled arm oscillations in the horizontal plane

When oscillating both upper limbs in the horizontal plane, stability and accuracy are much lower during isodirectional (ISO) than antidirectional (ANTI) coupling. Recent results suggest that the lower coordination in ISO may be mainly linked to i) the interference between anticipatory postural adjustments and voluntary commands in arm muscles and, ii) the higher muscular effort spent for postural aims. The present study will 1) quantify the supplemental effort required by ISO coupling, 2) establish whether it can be ascribed to postural activities, 3) compare it with the effort paid for the primary movement. Breath-by-breath metabolic (VO2, VCO2) and cardio-respiratory (HR, VE) parameters, together with the reaction forces and the torque about the trunk vertical axis (Tz) exerted on ground, were measured in six subjects, who performed cyclic (1.4/2.0Hz) arm adduction-abduction in the horizontal plane, with either one arm or both arms, ISO or ANTI coupled. At metabolic steady-state, the mean VO2 and Tz were larger during ISO than ANTI coupling. Moreover, during ANTI, virtually all the energy was spent for the primary movements while the large increase in VO2 when passing from ANTI to ISO was almost entirely ascribable to postural activities and linearly related to Tz.