Muscle Growth: Slow Reps vs. Fast Reps - Which is More Effective?

When training to increase strength and muscle mass, we often prioritize factors such as the weight lifted, the number of repetitions, and the specific exercises performed. However, there are other variables that deserve attention, including the speed at which we perform movements. The question arises: Should we perform movements slowly or quickly? Is it more effective to have a slow lifting phase and a fast lowering phase, or vice versa? Let's explore the impact of controlled pacing on our training results.

Build Muscle and Increase Strength with the Right Repetition Speed

Components of Movement: Concentric, Isometric, and Eccentric Muscle Actions

A single repetition consists of three main muscle actions: concentric contraction (muscle shortening), isometric contraction (muscle tightening without shortening), and eccentric contraction (muscle lengthening). Each of these actions has different benefits, and it can be beneficial to vary the speed for each.

Total Time Under Tension (TUT) refers to the total time your muscles are under tension during a set. It's calculated by adding the time for all three muscle actions in each repetition. By increasing your TUT, you can promote muscle growth.

For example, if each repetition takes five seconds and you do ten repetitions in a set, the total TUT for that set would be 50 seconds. You would continue to add up the TUT for all sets that target the same muscle group until the end of your workout.

While it's often recommended to perform exercises slowly to increase TUT, it's important to note that different muscle actions benefit from different speeds. We'll explore this concept further to understand how to optimize speed for each type of contraction.

Concentric Phase: Building Strength and Power

The concentric phase is when your muscles shorten to overcome resistance. This is the lifting part of exercises such as pushing the barbell up in a bench press or rising from a squat. In pull-ups, it's the act of lifting your body weight.

For muscle growth, the speed of the concentric phase can have some flexibility. Slower, controlled movements can increase time under tension (TUT), but may require lighter weights due to fatigue.

However, to improve strength, focus on a strong concentric phase. This doesn't necessarily mean moving at breakneck speed, but rather with explosive intent. Imagine forcefully pushing the weight away in a bench press, even if the observed speed seems moderate. The key is to maximize power output within your capabilities and maintain good form.

This distinction between actual velocity and intended velocity is important. Focus on moving the weight as quickly and forcefully as possible with proper technique, not on achieving an unrealistic outward velocity.

Isometric / Pause Phase

The isometric phase occurs between the concentric and eccentric phases. In the bench press, it's when the barbell is fully extended or touching the chest. In this phase, it's essential to take the time needed, regardless of speed.

To increase muscle mass, it may be beneficial to hold for a second at the point of maximum contraction in exercises where applicable. While the bench press has an isometric phase, it's not as effective for hypertrophy as the isometric phase in pull-ups.

When the arms are fully extended during the bench press, we don't feel as much activation in the chest compared to the feeling in the lats when we hold ourselves up with the chin above the bar during pull-ups.

For exercises like pull-ups, hip thrusts, bicep curls, or lateral raises, it's beneficial to hold for a second between the concentric and eccentric phases to provide an extra stimulus.

For increasing muscular strength, the isometric phase should allow us to take a breath and prepare ourselves physically and mentally for the next repetition. When training basic strength exercises like deadlifts, bench press, or squats, this phase helps stabilize after performing the explosive concentric phase.

Isometric Phase: Holding for Control and Strength

The isometric phase is a brief moment of static muscle contraction that occurs between the concentric and eccentric phases. In exercises such as the bench press, this occurs when the barbell is momentarily locked at the top (chest press) or bottom (chest touch). While there's no movement, isometric holds still contribute to the overall effectiveness of the exercise.

For hypertrophy (muscle growth), isometric holds can be beneficial in some exercises. A short hold (about one second) at the peak of the contraction can provide an additional stimulus for growth. However, the effectiveness of this technique varies from exercise to exercise. For example, holding at the peak of a bench press may not be as beneficial to chest growth as holding at the peak of a pull-up (where lat activation is much higher). Exercises such as pull-ups, hip thrusts, bicep curls, and lateral raises can benefit from a short isometric hold to maximize muscle engagement.

In strength training, the isometric phase serves a different purpose. It allows you to take a controlled breath and mentally prepare for the lowering (eccentric) phase. This brief pause helps stabilize the body after the explosive concentric movement, especially in compound exercises such as deadlifts, squats, and bench presses.

Finding the Right Repetition Speed for Muscle Growth

While the previous sections explored the different muscle actions in a rep, the question remains: how slow or fast should you perform each phase for optimal muscle growth (hypertrophy)?

For a long time, the focus was on maximizing time under tension (TUT) by extending the eccentric phase. However, research shows that excessively slow repetitions (over 8 seconds) can hinder hypertrophy. This is likely because very slow movements require lighter weights, which may not stimulate muscle growth as effectively.

A 2015 review found that repetitions lasting between 0.5 and 8 seconds showed no significant difference in muscle growth. The key takeaway is that speed and weight both matter.

See also: How to Increase Muscle Mass: Strength or Hypertrophy?

The isometric component should be short to maintain constant tension, muscular ischemia and hypoxia, all of which stimulate hypertrophy. However, the effectiveness of this aspect depends on the specific muscle area where the peak force occurs.

For example:

  • In a standing biceps curl, peak tension occurs in the middle of the movement. Therefore, it doesn't make much sense to rest with fully extended or fully flexed arms.
  • However, in a hip thrust or lateral shoulder raise, where the peak force occurs at the end of the movement, it is beneficial to rest briefly at that point.

Remember, finding the right balance of speed, load, and rest duration will help you achieve the perfect repetition for your fitness goals.

Practical Application

When it comes to repetitions, there's no one-size-fits-all approach. Focus on controlled movements and pay attention to the specific muscle group you're targeting, rather than obsessing over the exact timing of each repetition.

Here's how to find the right balance:

1. Slower Repetitions: These increase time under tension, but may limit the weight you can lift. While they're effective, be careful not to go too slow. During the concentric phase (when you are lifting the weight), you want to avoid excessively sluggish speeds.

2. Faster Repetitions: These reduce the time under tension, but allow for heavier weights. If you're looking for strength gains, faster reps can be beneficial. However, maintain proper form and control.

Now let's look at specific speeds based on your goals:

Muscle Growth (Hypertrophy):

  • Eccentric Phase: 3 seconds
  • Isometric phase (if applicable): 1 second (or none, depending on the exercise)
  • Concentric phase: 1 second
  • Total repetition time: Approximately 5 or 6 seconds

Muscular Strength:

  • Eccentric phase: 3 seconds (or 2 seconds if you prefer)
  • Minimal isometric phase (just enough to control the weight)
  • Explosive concentric phase
  • Total repetition time: Approximately 3 seconds

Remember that individual variation and specific goals are important. Adjustments may be necessary to find the best approach for your specific needs. By applying these principles, you'll optimize your training for both muscle growth and increased strength.
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