Aim: 

When performing associated movements of the upper limbs in the horizontal plane, the postural engagement is much higher during isodirectional (ISO) than antidirectional (ANTI) coupling. It may be assumed that, being the moving masses identical in the two cases, any difference in the metabolic cost between the two coupling conditions may be attributed to the involvement of postural musculature. Oxygen uptake (VO₂) was therefore measured during ISO and ANTI coupling.

Methods: 

Six participants underwent 4 exercises each consisting of intermittent trials (12 s movement, 12 s rest) of cyclic adduction-abduction with both arms in the horizontal plane, either in ISO or ANTI coupling and at both 1.4 and 2.0 Hz. Each exercise lasted 5 min. During exercises we recorded the torque (Tz) about the trunk vertical axis exerted on ground, as a global index of postural engagement, and breath-by-breath gas exchanges and heart rate (f_H).

Results: 

At steady-state (last minute of each exercise) it resulted that:

i) the amplitude of Tz ANTI (Nm SE) was 0.5 0.2 at both 1.4 and 2,0 Hz, indicating a minimum postural engagement; while Tz ISO raised to about 19 2 and 27 3, respectively (ANTI vs ISO: p always <0.0002);

ii) VO₂ ANTI (ml·min^-1) was significantly lower than VO₂ ISO at both 1.4 Hz (477 45 vs 781 73 p < 0.002) and 2.0 Hz (631 80 vs 1493 160, p < 0.0002); iii) f_H ANTI (b·min^-1) was significantly lower than f_H ISO only at 2.0 Hz (106 10 vs 14 8. p < 0.0002).

Conclusion: 

The above results show that the large difference in VO₂ between ANTI and ISO exercises should be totally ascribed to a change in the energy expenditure related to postural requests, which are negligible in ANTI and conspicuous in ISO coupling.