Slow Reps vs. Fast Reps: How to Stimulate Muscle Growth


What's your approach to lifting weights? Do you perform each set slowly or rush through the motions? Even though most experts recommend a moderate tempo, this isn't always the case. Both fast and slow reps have their benefits, and each will generate different results. The question is: which one works best for muscle building? Let's discuss each approach!

The Pros and Cons of Slow Reps
Lifting weight slowly increases the time under tension, giving you better pumps. In theory, this approach makes it easier to fatigue your muscles, leading to faster growth. The positive phase of a rep should take about four seconds, while the negative phase should last for another four seconds. Ideally, you should hold the contraction for at least two seconds.
Slow reps put greater stress on your muscles, creating microtears. This promotes hypertrophy aka muscle growth. It's not unusual to see athletes who complete "super slow" sets that may last for as long as 20 seconds.

However, lifting weights slowly isn't necessarily better. With this approach, you won’tbe able to handle heavy loads. Training for hypertrophy involves lifting 75 percent of your one rep max for at least eight reps. Since you're spending a lot of time under tension, you can not lift 75 percent of your one rep max. Thus, your gains will be limited.

The same goes for ab training where weights are rarely involved. Studies have found that doing crunches as fast as possible increases the activity of all four core muscles, especially the obliques. At slow speeds, the obliques were less stimulated but their activity increased.

Basically, doing crunches fast allows you to recruit more muscle fibers and hit the obliques more efficiently.

What about Fast Reps?
This approach involves performing each part of a rep in one or two seconds. It results in a more challenging, explosive workout that leaves your muscles burning. Moreover, it raises your heart rate and increases metabolism, leading to a higher energy expenditure.
Fast reps are widely used in metabolic training for their ability to torch fat. This strategy allows you to lift heavier weights and recruit more muscle fibers. On top of that, you'll take shorter breaks, keeping your heart rate up. It's a great way to burn fat, build muscle, and boost your endurance. Your power and explosiveness will increase too.

Fast Reps vs. Slow Reps: The Verdict
A number of studies have found that subjects who performed slow reps experienced greater gains in bicep size compared to those using fast reps. It appears that lifting with a slow, controlled motion is better for hypertrophy, but not for strength. Fast reps have been shown to produce greater gains in muscle strength and endurance.

As you see, both options have their perks. Choosing one depends on your goals. Repetition speed does matter, but it's not everything. From diet and workout intensity to training frequency, there are many other factors that influence your gains.

Decide whether you want to get stronger or just build muscle. Fast reps make it easier toattain a maximum power output, which translates into greater strength. Slow reps are more efficient for hypertrophy. If you're not sure which option is best for you, feel free to experiment. Try both approaches and track your progress.

If your goal is to stay fit, repetition speed is less important. Be consistent, lift heavy, and keep your routine varied. Watch your diet and adjust it according to your goals.


  • Both slow reps and fast reps have their perks. 
  • Slow reps work best for hypertrophy, while fast reps increase strength, power, and explosiveness. 
  • Choosing the best approach depends on your goals. 
  • Repetition speed is just one of the many factors that influence your progress. Workout intensity, nutrition, and training methods play a role too.