Is the Nervous System what's limiting Aerobic Capacity in Runners?

This expert from the book Running Science explores the influence of the Nervous System on VO2 Max and Aerobic Capacity. In bold are my highlights.

it is possible that the cardiovascular system is not capping VO2max.

As T.D. Noakes and A. St. Clair Gibson have noted, overall muscular performance and thus the oxygen-consumption rate during running are determined by the nervous system’s recruitment of motor units (collections of muscle cells) inside the leg muscles.

If this seems confusing, remember that the muscles cannot act alone during running; they must wait for commands from the brain and spinal cord in order to engage themselves in the act of running. A sustained, high level of muscle engagement by the nervous system would inevitably lead to a high VO2max in an individual runner. In contrast, a more limited level of recruitment would produce a lower VO2max, even in a case in which a runner had ample reserves for oxygen shipment and use in the heart and leg muscles. As Noakes has observed, runners with higher values of VO2max appear to have nervous systems that not only recruit a greater number of muscle cells during intense running but also sustain this recruitment for greater than average time periods. This observation has important implications for training.

Basically, the research on neural output means that in order to maximize VO2max and performance, endurance runners must train their nervous systems in ways that optimize motor-unit recruitment. This can hardly be accomplished by high-volume, submaximal training, the traditional way to train for VO2max enhancement, since motor recruitment during such work is modest. Rather, it can only result from highly intense, Kenyan-style training that relentlessly provokes greater neural outputs and motor-unit activations. For an individual runner, the key to developing the highest-possible VO2max appears to involve optimizing motor-unit recruitment, with supporting roles played by expanded heart and leg

Source: Running Science, Anderson, p. 80