Is it necessary to employ whole body training in order to work at your VO2max? It appears not.
An athlete can train at their VO2max by recruiting about 50% of their muscle mass, e.g. the leg muscles. By adding arms to the exercise mode, no increase in VO2max will occur. Even though the capacity of muscle groups is to keep on working, the heart just can’t pump enough blood to all muscle groups whilst maintaining blood pressure.
So it’s quite simple: if you want to train at your VO2max, train your legs!
Astrand & Saltin (1961b), Stenberg et al. (1967)