Final answer:
Motor units involving Type II fibers are activated by larger, fast conducting neurons, necessary for powerful muscle contractions when heavy strength is needed.
Step-by-step explanation:
Motor units that involve Type II fibers are typically activated via larger, fast conducting neurons. These neurons have axons that can transmit action potentials quickly over long distances to activate the necessary muscle fibers for contraction. When more strength is needed from a muscle, such as lifting heavy objects, larger motor units are recruited, which are connected to Type II fibers.
These larger motor units are controlled by larger motor neurons, which are higher-threshold and activate the larger muscle fibers to generate more contractile force.