Training for maximum power requires you to recruit the high-threshold motor units. To recruit them, you must lift maximal loads (>85% of 1RM) or you must lift submaximal loads (50-75% of 1RM) with high acceleration so the actual lifting velocity is fast.
There’s a simple way to ensure that you get maximum power from each set: limit the duration of each set to 10 seconds or less. Why?
It has to do with the endurance capabilities of your high-power motor units. Your largest motor units are known as fast-twitch, fast-fatigable (FF) motor units that contain a large bundle of type IIb muscle fibers. Type IIb fibers have a very limited capacity of energy so they fatigue within 10 seconds. After you recruit the FF motor units, it’s tough to keep activating them because they don’t recover quickly.
However, the second most-powerful motor units come from the fast-twitch, fatigue-resistant (FFR) motor units that contain type IIa muscle fibers. Like all motor units, they range in size and endurance. You have FFR motor units with fewer muscle fibers that get activated before a FFR motor unit that’s any larger. In other words, you have FFR motor units that are bigger and stronger than others. The largest ones have the lowest endurance capacity. So by keeping your sets to 10 seconds, or less, you’ll target and develop the most powerful FFR motor units that have plenty of growth and power potential.
With heavy loads, this 10-second rule is easy to follow because you can’t go past 10 seconds, even if you tried. For submaximal loads, it’s much easier to screw up. As a gross generalization, shoot for three reps per set with submaximal loads.
For example, when you need to build explosive power, start with a load that allows around 20 reps. For those of you who like percentages, this is around 60% of your 1RM. Then, perform only three explosive reps for 10 sets with approximately 45 seconds of rest between each set. This ensures that each set lasts less than 10 seconds, the actual lifting velocity remains fast, and stay far away from failure. Remember, when you approach failure motor units start dropping out.
So whether you’re training heavy, or light and fast, limit the duration of your sets to 10 seconds and you’ll build new muscle and power fast!