Difference in the metabolic cost of postural actions during iso- and antidirectional coupled oscillations of the upper limbs in the horizontal plane

When oscillating the upper limbs in the horizontal plane, the effort required to maintain posture is higher when the limbs move isodirectionally (ISO coupling) than when they move mirror symmetrical, i.e., antidirectionally (ANTI). Movements stability and accuracy are much lower in ISO than in ANTI and the higher postural requests may be one factor contributing to the coordination deficiency of ISO movements. On this background, we measured the metabolic cost of ISO and ANTI movements in order to (1) quantitatively evaluate the supplemental effort required by ISO coupling, (2) establish whether it can be entirely ascribed to postural activities, and (3) compare it with the effort paid for the primary movement. Breath-by-breath metabolic ((V over dot O-2, (V) over dot CO2) and cardio-respiratory (HR, (V) over dot E) parameters were measured in six participants, who performed intermittent exercises (5 min long, 12 s movement, 12 s rest) of cyclic arm adduction-abduction in the horizontal plane with either one arm or both arms in ISO or ANTI coupling, at 1.4 and 2.0 Hz. A force platform recorded the reaction forces to ground and the torque about the trunk vertical axis (Tz). At both frequencies and at metabolic steady-state, the mean values of both (V) over dot O-2 and Tz were found to be larger during ISO than ANTI coupling. Moreover, a linear relation was found between metabolic cost and Tz. Lastly, during ANTI coupling virtually all the energy was spent for the primary movement whilst the large increase in energy expenditure when passing from ANTI to ISO was almost entirely ascribable to postural activities.