If you're an experienced weight lifter you know all about the plateau. You try and push through by doing more weight, less weight, or try doing something a body builder told you about in Muscle and Fitness. We end up plateauing often because of poor long term programming, trying to much weight too early, or not adequately regenerating our body through diet, sleep, and recovery.
Our body also loves to adapt to what it's doing. That's why after living in San Diego for four years not, it's hard for me to go back to Vermont on the days when you spit and it will freeze before it hits ground. This (adapting not spitting) is called the SAID principle, Specific Adaptations to Imposed Demands, fancy way of saying our body and mind try to adapt to our environment. That's why all the great strength coaches will changes phases with regards to volume, intensity, and tempo.
In Daniel Coyle's book The Talent Code, he talks about how great athletes, musicians, and performers go into deep/deliberate practice by either slowing the task down or speeding it up. This always for the brain and body never to become comfortable or completely adapted. By either slowing it down or speeding it up, one also becomes incredibly engaged and aware, focusing all energy towards improvement. Depending on what your trying to accomplish one might be better for the other, but for many skills, using both is a viable option that can be programed.
Lets apply this to the weight room. Even with guys who are trying to get stronger, many consistently stay in a comfort zone that labels them to their sport. Getting out of this comfort zone helps develop skills. In this case its strength and power, two concepts that all athlete's look to improve.
Deliberate Practice: Power
Power is often developed through Olympic lifts, plyometrics, med ball throws, and kettlebell swings. If we looked at the two options of deliberate practice, undoubtedly speeding it up would have to be the best option. You really can't move powerfully, slowly. It's so awkward that you can't even say it in a sentence correctly. A great way to make sure you bust through a power plateau is to reduce the weight and focus on the speed of the bar. Put your feet through the floor and make the bar move with purpose! Program this in early on, but don't be afraid to periodize a "light" week within a heavy block.
For example, in a 4 week phase that is going from 80-87.5% into another 4 week phase that goes into the heavier 90-95%, it might be smart to go back down to 60-75% in the last week in between phases. I heard Bill Hartman talk about how they accidentally stumbled upon this technique that works wonders for them at iFast (though their %'s may differ).
Deliberate Practice: Strength
We can use the same technique as above by reducing the weight and moving the load faster. Especially on the concentric phase, letting go of some of the weight and really working on the speed of movement has helped me and my athletes get through plateaus that we hit.
Another option is to slow the tempo of the weight, especially on the eccentric phase. Often coined eccentrics or negatives, be prepared for some serious DOMS. Again you must reduce your weight especially when going for 5-10 repetitions. Many strength coaches will include this as an eccentric phase for 3-4 weeks. Slow concentric movement is usually frowned upon, but if it's only for 3-4 weeks it might not be a bad idea to try controlling the bar on the way up as well.
What really makes this interesting is relating deliberate practice, which is proven to improve skills over time, to increase power and strength. These techniques that many strength and conditioning coaches use to progress physical tools, it also may be influencing cognitive connections as well with our ability to learn the movement more efficiently by focusing on it in a completely different way. I don't have any research to back this up (yet?) but my guess is we would see some pretty cool brain activity going from these different phases. That's just the geek in me.
These techniques can also differ from person to person. If a linebacker has been benching in the 85-95% range since they were in high school, I will put down a lot of money that taking some time in a lower percentage and speeding up/slowing down will improve there power and strength. If you took the opposite, a female XC runner, who only uses dumbbells under 20 lbs for 15-25 reps, it maybe time to change the speed or weight of the movement to create progression in the body and brain.
Note that these phases do not need to be long term, but are useful for creating new avenues in the body and brain for strength and power to be developed. Maybe I'll coin it muscle confusion......HAH!