Apnea Rush (無呼吸打撃, Mu Kokyū Dageki) is Spec's fighting technique.
By controlling his breathing algorithm, Spec is capable of unleashing over a hundred punches and kicks within the span of a few seconds, which are so fast that counterattack is near impossible. This allows him to 'melt' walls, metal and even human bones.
He is capable of holding his breath for five minutes while attacking so his barrage doesn't end until his opponent lies in a lifeless heap of flesh. Spec's ability to hold his breath for five minutes is an important part of this technique. In normal combat, the moment a fighter pauses to take a breath between attacks provides an opportunity for their opponent to counterattack. Apnea Rush doesn't have this weakness.
He used it during his fight against Kaoru Hanayama in the second series of the manga. The strength of his punches and kicks are enough to damage the Statue of Liberty. Hanayama's high pain tolerance is what allowed him to both survive and made him the first to counter it.