Automotive; in a four-cycle engine, when the piston is moving down in the cylinder (its bore) after ignition and prior to exhaust. The explosion/rapid expansion of the ignited fuel/air mixture forces the piston down its bore, pushing the crankshaft in a circular motion. See also: compression stroke, intake stroke, exhaust stroke.

The force and motion producing step (before the rigor state) in which the interaction of the thick and thin filaments of sarcomeres (the basic contractile unit of muscle) generate tension that causes muscle contraction.