Oxygen uptake transients at the onset and offset of arm and leg work

he halftimes (t_1/2) of the V̇_O2 on- and off-responses have been determined on 4 moderately active subjects (1) in arm cranking ( V ̇_O2 ∼- 1 1/min), (2) in leg pedaling at 4 graded submaximal ( V ̇_O2 ∼- 0.8 to 2.51/min) work loads, and (3) when superimposing arm cranking on preexisting leg pedaling, both in the supine and in the upright position. In supine experiments the mean t_1/2 of the V̇_O2 on-response was longer for arm cranking than for leg pedaling (64 vs 44-49 sec)at equal _O2; however, at the same percentage of arm and leg V̇_O2 max the respective t_1/2 were similar. In sitting experiments all t_1/2 of the V̇_O2 on-response were shorter than when supine, but the t_1/2 for the arms were still slightly longer than those for the legs. When arm cranking was superimposed on preexisting leg pedaling, the t_1/2 for arms was reduced both in the supine (from 64 to 35-38 sec) and in the sitting position (from 44 to 40 sec). The halftimes of the V̇_O2 off-response were much shorter (20-32 sec) than those of the on-response and similar in all experiments. In all conditions the V̇_O2 deficits at work onset were considerably larger than the fast component of the corresponding V̇_O2 debts during the first minutes of recovery. The difference was totally accounted for by anaerobic glycolysis occurring early during the V̇_O2 on-response, particularly in arm exercise. It is concluded that at submaximal work loads the O₂ deficit is accounted for by the fast component of the O₂ debt plus the O₂ equivalent of the early lactate production.