“Slow and controlled” is probably the most common bit of coaching that you’ll hear from a personal trainer while you’re doing any exercise. This is because performing an exercise in a slow and controlled manner reduces your reliance on momentum to move the weight. Reducing momentum increases the quality of contraction and increases time under tension, thus increasing the potential to stimulate hypertrophy.
Performing negative or eccentric reps too slowly can significantly reduce the mechanical stress of each rep, thus reducing its potential to stimulate hypertrophy.
Eccentric contractions are known to produce a more potent stimulus for growth than concentric contractions.
Research from McMaster University recently demonstrated that fast eccentric contractions (<1 second down) produce greater muscle damage (i.e., Z-line streaming) than slow eccentric contractions (>3 seconds down).
This same group also demonstrated that fast eccentric muscle contractions lead to greater strength and size gains than slow eccentric contractions over time.
Fast eccentric contractions lead to greater gains in size and strength than comparatively slow eccentric contractions.
Although it’s important to control the weight as you perform any exercise, purposely moving the weight unnecessarily slowly may reduce the exercise’s effectiveness. During traditional sets, use a onesecond- down tempo to increase the growth potential of each rep. When doing “negatives,” or sets in which you are focusing specifically on eccentric reps, use a weight heavy enough so lowering it at a one-second tempo is all you can do. Be sure to use a spotter whenever you are performing negatives. – FLEX