3. Target High-Threshold Motor Units with an Isometric Pause. High-threshold motor units are the fast-twitch or powerful muscle fibers. An excellent way to target them is with an isometric pause in the advantageous position (where the body is strongest based on lever length). For flexion exercises, such as biceps or hamstring curls, you should pause in the down position for 1 to 2 seconds. For extension exercises such as squats or bench presses, pause in the up position between the concentric and eccentric motions, when the limbs achieve near lockout position.
Of course, varying tempo allows you to perform an isometric pause in the disadvantageous position when you have poor leverage as well. The disadvantageous position for flexion exercises is the up position, and for extension exercises it is the down position. You can imagine that holding the bottom position of a squat for 1 or 2 seconds would provide a valuable training stimulus while increasing intramuscular tension, a combination that can further boost strength development.
Take note that it is necessary to train high-threshold motor units and develop maximal strength in slower lifts such as the squat, deadlift and bench press in order to improve faster on movements such as Olympic lifts. For example, you cannot power snatch 100 kg unless you can squat about 184 kg. If you can back squat only 160 kg, you won’t be able to snatch 100 kg until you increase your squat weight significantly. Varying tempo is an ideal way to work on this.