You know when you’re in the gym and you see someone doing those bicep curls super fast? I’m talking to the point where you may think it looks pretty stupid. Now what if I were to tell you that doing these faster reps, better known as speed reps, may activate more of your super fast-twitch muscle fibers to get you stronger quicker.

Let’s start with the simple science behind it. Each time you do an exercise, your body is performing work (hence the name “workout”). Power is defined as the amount of work done over time. To be more clear, the less time it takes for you to expend a certain amount of energy, the more force and power it requires to get the initial movement started. So by performing the workouts faster you will force your body to activate its super fast twitch muscle fibers so that they can produce the explosive movement.

Doing slower, more controlled movements place the muscle under more stress since the muscle is performing work for a longer period of time (great for hypertrophy and building size), but fast reps are great for power and gaining strength. This is why you see lots of professional athletes doing this type of explosive training. They do squats with a pause at the bottom and then jump up as high and as fast as they can. They also do shrugs with a pause at the bottom and then jump up with the weight explosively pulling it into their traps. For example, football is a sport that requires explosive, quick movements. The more you engage the super fast twitch muscle fibers during training, the faster they are able to fire during the game.

When you do a movement in a slow, controlled movement, you are working specifically on hypertrophy, which is a where the muscle fibers are forced to grow in size. Muscle size is not directly correlated to strength, however. This is why some powerlifters who weigh 150 pounds are significantly stronger than 300 pound bodybuilders. Speed reps allow you to train with heavier weights, which will help increase your strength. When your force your body to produce a very explosive movement with a heavy weight in a short period of time, your muscle fibers are forced to fire much more rapidly. You will notice that by increasing your rep speed, you can lift more weight even at smaller speeds. Working with heavier weights has its advantages when it comes to building strength. The biggest thing to recognize here though is that you cannot sacrifice form for the weight you are using.

People often mistake fast tempo to mean bad form. It is bad form and lack of warm up that cause injuries, not necessarily fast lifting. You are required to keep proper form while performing the movement, but just do so at a faster rate.

Remember, safety is always a priority. Always remember to maintain good form and do a full range of motion when lifting fast. I am not saying that when you do a bench press you should bounce the weight off your chest. I am not saying to swing your back backwards and forwards to hoist up that barbell curl. I am saying to do everything in a controlled manner but do so in a faster motion on the concentric portion of the movement. Follow something along the lines of 3 seconds on the way down and 0.5-1 seconds on the way up.

Should you do this all the time? NO. Building muscle is all about variety. Doing speed reps is something you should incorporate in your routine. Try a few exercises a week that utilize just speed reps. Or every month or so, devote one full week to just speed rep training. This does not mean there is no place for slow lifting. If you want to see maximum results, you should keep your muscles guessing and you should mix up the tempo and consistently change around your routine. However, speed reps are more effective at increasing strength and raw power faster than slow movements are.

Source

http://www.simplyshredded.com/the-need-for-speed-accelerate-your-muscle-growth-by-manipulating-the-speed-of-your-reps.html

http://www.musclemag.com/muscle-building/the-perfect-rep-speed-for-growth/#.UJgZGWnuVnQ