Slow Reps Vs Fast Reps for Optimal Muscle Growth

Welcome to one of the oldest issues in the world of bodybuilding: slow reps vs fast reps for hypertrophy ? How fast should you lift for optimal muscle growth?

There have been different answers to these questions over the last two decades from various experts and scientists and that has made the matter even more complicated and confusing that it actually is.

In this article we’ll try to shed some new light upon this debate and ultimately help you achieve better results by adequately adjusting your rep tempo.

Slow Reps vs Fast Reps for growth ?

Rep tempo or lifting speed is basically the rate at which you perform reps in a given set. Some personal trainers will tell you that the best way to lift is explosively, thereby maximizing fiber recruitment and triggering greater growth, while others claim that lifting in a slow and controlled manner, especially on the eccentric portion of the movement, will create greater muscle tension and lead to greater hypertrophy. And then there are those who swear that frequently varying the speed is the key lifting technique for optimal gains.

So Which of These Opinions is the Closest to the Truth?

For starters, it’s a fact that a slow rep tempo will reduce the amount of weight you can handle and you’ll end up performing less work than you would with a high-velocity movement.

But still, it’s also true that time under tension tends to be significantly greater at slower velocities and muscles get stimulated for a longer period of time. Therefore, manipulating the tempo will produce important differences in muscle adaptation, based on its effects on the correlation between volume and time under tension.

But most recently, a meta-analysis on the subject, involving data from eight controlled trials that compared the effects of different training tempos on muscle hypertrophy, showed that there are no significant differences in hypertrophy between lifting with a rep tempo of half a second and eight seconds, in terms of training to the point of muscular failure. It seems that the specific benefits of both slow (greater time under tension) and fast velocity training  (more volume) get evened out and in the end both tempos produce similar results.

However, there seems to be a threshold beyond which slowing down the lifting speed has negative influence on hypertrophy – when reps last for 10 seconds or longer, the amount of weight you can lift is dramatically reduced, resulting with an equally reduced muscle activation.

And this inability to recruit the full spectrum of muscle fibers is ultimately detrimental to both strength and size gains, so it’s safe to say that super-slow lifting is not the best idea for maximizing your growth.

Concentric vs. Eccentric Tempo

The previously discussed findings inspected the effects of different total rep durations but left out the influence of varying the tempo on the concentric and eccentric portions of the lift.

Unfortunately, only a small number of studies have tried to determine optimal concentric and eccentric tempos for muscle growth.

One of them, that explored hypertrophic adaptations between different concentric and eccentric tempos under traditional training methods, split 28 women with previous training experience into two groups: one performed lower body exercises with two-second duration of the concentric portion and a 6 second duration of the eccentric portion of the movement, while the second group trained on the reverse way – with a 6 second duration of the concentric and two-second duration of the eccentric portion. That being said, the load and total time under tension were equal for both groups.

The results showed a similar hypertrophy of type I fibers between the groups after nine weeks of training, but the group who performed slower on the concentric part had greater increases in type II fiber than the group who performed slower on the eccentric part. However, these results cannot be made into definitive conclusions, given the many methodological flaws and practical limitations of the study.

Take Home Message

The limited number of studies and their lack of in-depth analysis of the issue make it almost impossible for us to draw objective conclusions about slow reps vs fast reps for muscle growth. In reality, lifters use a wide range of lifting speeds to stimulate optimal hypertrophy and the results vary greatly from one individual to the other.

Still, there are a few things we can say for sure:

  • Taking more than three seconds on the concentric portion of the movement reduces the effectiveness of the exercise in terms of muscle activation.
  • Eccentric portions should be performed in a way that enables sufficient muscular tension, meaning that you shouldn’t let the forces of gravity do the work. Controlled doesn’t necessarily mean super slow.
  • If you want to increase time under tension, it’s best to use slow tempo on the eccentrics and perform the concentrics explosively.
  • If you want to keep on building muscle at a relatively steady rate, you could benefit from varying the rep tempo every 4-6 weeks in order to recruit different muscle fiber types.

Essentially, manipulating with rep tempo can definitively help you maximize the effectiveness of your workouts, but until science provides us with more definitive answers, you will need to find out, between slow reps vs fast reps, what works best for you, based on the basic rules we’ve uncovered in this article, and keep pushing yourself beyond your limits.

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