** Note: The slow negative portion of the lift does not apply to the kettlebell swings and waiter's walks. (sixstarpro.com)
That being said, in order to cause the most muscle damage possible, avoid spending long amounts of time during the easiest part of the lift, for example at the top of a bench press, because that portion of the movement brings the least amount of stress on the muscles, and aim to spend more time on the eccentric, or negative portion of the movement, when the muscle is slowly elongating. (fitnessandpower.com)
Keep your abs tight and go super-slow on the negative portion of each rep. (fitnessandpower.com)