The debate for rep timing has been going on for as a long as hypertrophy has existed. The argument stems from a number of different things, but I’d imagine that part of it is the age-old “bodybuilder vs. powerlifter” debate on explosiveness generating strength and extended time under tension generating muscle growth. I’m of the religion that both can be extremely useful in certain circumstances, however, shedding light on the various methods and their scientific background can be beneficial.

The Science:

http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.2011.221200/full

Summary:

When comparing the results of Time Under Tension (TUT) during Leg Extensions, slow lifting movements performed to fatigue produces increased rates of muscle protein synthesis than the same movement performed rapidly.

“The results suggest that the time the muscle is under tension during exercise may be important in optimizing muscle growth”

What it means

What this study does not test are the optimal numbers for growth. They only attempted to test whether TUT in any form is beneficial for muscle growth vs. explosive 1 second up and 1 second down reps. They discovered that 6 seconds up and 6 seconds down were better than the explosive method, but it didn’t say whether 7s up / 7s down was better than that, etc.

What I mean by 6 seconds up and 6 seconds down is that when doing a bench press you push up for a 6 second count to the top of your range of motion and then when bringing it down it takes 6 seconds to reach your chest. This requires a lot more endurance than the explosive method and while you may be performing the same number of reps, your muscles are put under much more stress.

An Alternative

One thing that most people don’t realize is that there are multiple methods to achieve time under tension.

You follow the 6 seconds up and 6 seconds down or whatever time you think is optimal. You do MORE reps than normal thereby your Time Under Tension increases without doing the mind numbing full 6 seconds up and down approach.

Both methods induce an incredible amount of fatigue and aren’t recommended for personal records or heavy sets. Rather, I’d suggest using somewhere around 30-70% of you 1 rep max. (Depending on which method you choose).

Optimal TUT

I don’t KNOW what the optimal Time under tension is, so hopefully you don’t leave this article furious over being tricked into reading. However, based on this study and multiple others done by people far smarter than myself, I can suggest that it DOES work. This gives you some fire power to argue when someone suggests otherwise. Don’t believe anyone who states that there is a perfect time for doing reps because everyone’s body is different, but it is clear that incorporating some additional time under tension into your workout CAN be effective.

In addition, both methods (Explosive and Slow TUT) can work on different muscle fibers important for hypertrophy. Check out this quote from Jim Cordova. One of the Natural Kings of Bodybuilding.

An explosive tempo, while keeping constant tension and working to or near failure, is a sound way to attack your fast-twitch fibers. This style will subject the muscles to a heavier weight than would be used at a slower tempo, leading to a favorable hypertrophic response. Although constructive, this tempo equates to less TUT, which will not thoroughly fatigue slow-twitch endurance fiber. On the other hand, a slower tempo places the muscles under a longer TUT, exhausting slow-twitch fiber to a greater extent, while simultaneously subjecting fast-twitch fiber to a unique form of tension. The bottom line is that both styles will be needed to maximize your potential for growth and refinement!

http://www.jimcordova.com/articles/details.php?id=40

In Conclusion, I don’t know what amount of time to recommend, but I CAN recommend to incorporate some more Time Under Tension into your workout if you don’t already.