While receiving fellatio (head) the man wraps his legs around the giver's head in a figure 4 headlock and locks the giver's mouth on his cock, forcing his cock all the way down the giver's throat. This is done without mercy and in the process, the airway is blocked, thus the giver cannot breathe.
This balls-deep penetration of the girl's/guy's throat is very stimulating and satisfying, both physically and psychologically.
Extreme usage of the Harlem Struggle can, and usually does, result in gag reflex stimulation leading to vomiting and also commonly leads to loss of consciousness from a lack of oxygen. This is the pinnacle of employing the Harlem Struggle: making the giver pass out.