Slow vs Fast reps – How quickly should you move during resistance training?
Should you perform slow reps when muscle growth is your goal? And what if you try to increase strength and power instead? Rep tempo matters a lot in strength training, and yet many athletes and coaches only focus on load and volume. This article answers how quickly you should move during resistance training, depending on your goal. Get ready for some myth busting…
Content menu:
- Why repetition tempo matters
- How quickly should you move during resistance training?
- Defining what’s a slow vs fast repetition
- When are slow controlled reps better?
- Fast vs Slow reps for hypertrophy (muscle growth)
- When are fast reps better?
- Slow vs Fast reps for strength and power
- Conclusion: rephrasing the question
- FAQ
We first talk about the benefits of slow reps and whether they are better for muscle growth. We’ll distinguish between the concentric and eccentric phase. We then talk about the benefits of fast reps and why you should implement them to improve muscular power and strength.
Why repetition tempo matters
Research shows that “a slower movement tempo decreases the maximum number of repetitions one is able to perform”, unless you decrease the load.
In other words: movement velocity determines how hard a set is, just like #repetitions and load.
So to get a complete picture of your training program, you should describe: movement velocity, #repetitions and load.
“Exercise volume is most often determined using the load and the number of repetitions, which can be overly simplistic.”– Scientific source
As the number of repetitions and load determine the muscle adaptation (e.g. strength vs muscle growth vs power), so does movement velocity. We’ll learn more about that in a bit.
All these reasons combined should emphasize the need to quantify and describe repetition tempo. The easiest way to do this is by using a so-called Velocity Based Training device. Metrics that VBT devices like GymAware RS and FLEX show:
- Rep duration (time under tension)
- Concentric rep duration
- Eccentric rep duration
- Concentric velocity
- Eccentric velocity
But should you aim for fast or slow reps?
How quickly should you move during resistance training?
Let’s answer a common question:
Science shows you should never move slower than 10 seconds per repetition during resistance training. In other words, there’s no reason why you should do super slow resistance training.
But there’s obviously more to it.
For instance, many coaches will say you should perform slow reps to increase muscle growth and fast reps to increase strength and power. Or they will tell you to move fast during the concentric phase and slow during the eccentric phase.
But is that backed by scientific evidence?
Defining what’s a slow vs fast repetition
Before we can look at slow vs fast reps, we need to distinguish between:
- Voluntarily lifting submaximal loads at a slow speed (= choice)
- Lifting heavy loads at a slow speed, while aiming to move as quickly as possible (= result)
Lifting heavy loads (e.g. 90% 1RM) at a slow speed is a result of the force-velocity or load-velocity relationship. It’s not a choice: you simply can’t lift heavy loads fast, even if you do your best.
In this article, slow repetitions are reps which are voluntarily lifted at a slow tempo. Fast repetitions are reps lifted as fast as possible (with maximal intent).
When are slow controlled reps better?
Summary: (only) use slow reps when you aim to improve technique, avoid momentum or increase time under tension. Continue reading to discover whether you should aim for time under tension in the first place.
Slow controlled reps are better when you’re new to a specific exercise and you’re aiming for a good lifting technique. Beginners should start with slow controlled reps to improve their coördination (also known as slow motion strength training).
“The neuromuscular system needs to understand the movement pattern before it can efficiently perform at a high rate.”
Travis Mash
Slow reps increase Time Under Tension (TUT)
Another reason to go for slow controlled reps is when you want to avoid momentum or increase the time under tension.
This study looked at the effect of rep velocity on time under tension. Participants performed five sets of the bench press exercise to failure, using 70% 1RM and three different tempos: regular, medium and slow. They found that slow reps result in a higher time under tension.
This again shows the importance of adding rep velocity targets (and live velocity feedback) as a variable in your training program. Simply because rep velocity:
- Determines the maximum number of repetitions one is able to perform
- Determines the load one is able to use
- Determines the time under tension
But does time under tension matter? Continue reading to discover why literature showed that:
“Even though the TUT of the half-maximal velocity group was 60% higher, the maximal velocity group showed almost 2x more strength gains!”
Or as coach Travis Mash says:
“Time under tension might not be effective in the way that it has been used in the past. However, it’s still important to…”
Travis Mash
Read his full article here: Time Under Tension: Effective or a Myth?
How slow should you move during resistance training
When using slow reps to improve lifting technique, the exact tempo is not super important. As long as you lift slow enough to show good form, and increase movement velocity over time.
A good way to quantify rep duration or rep velocity is by using a velocity device.
Do keep in mind that super slow strength training or slow motion strength training, e.g. 10s per repetition, is scientifically proven to be inferior, when muscle growth is your main goal.
Talking about muscle growth…
Fast vs Slow reps for hypertrophy (muscle growth)
Summary: slow reps or not per definition better for muscle growth than fast reps. Continue reading why you should distinguish between the concentric lift and the eccentric muscle contraction.
Many coaches believe slow reps are better for muscle growth (hypertrophy). But is that true?
The increase in time under tension (TUT) could theoretically increase muscle growth. However, science shows that while slow reps increase TUT, they also decrease the number of repetitions in a set to failure. This could theoretically decrease hypertrophy.
You can solve a decrease in reps by decreasing the load, but this could also negatively affect hypertrophy.
The fact that you cannot change one (e.g. tempo) and keep the others equal (e.g. reps, load and fatigue), makes it hard to isolate the effect of rep velocity on muscle growth. So far, science shows no clear evidence for slow versus fast reps for hypertrophy, although it tends to lean more towards faster reps.
We’ve created a hypertrophy training program that you can use straightaway, while it also teaches you how to create any hypertrophy training program, using 3 core principles:
To draw a practical conclusion nevertheless, we must distinguish between the concentric and eccentric movement.
Concentric vs Eccentric movement
The lifting phase of an exercise requires a concentric muscle contraction. The lowering phase requires an eccentric muscle contraction.
Due to gravity, it’s hard to lift a heavy load fast (fast concentric), while it’s also challenging to lower a heavy load slowly (slow eccentric).
So it should come as no surprise that many coaches, backed by scientific literature, recommend aiming for a fast concentric phase and a slow eccentric phase. Especially when muscle growth is the goal.
Live feedback is the best way to promote a fast concentric and slow eccentric movement. GymAware RS and FLEX enable you to:
- Create a training program with rep duration or rep velocity targets
- Get live feedback on your concentric vs eccentric duration and velocity
- Track progress over time, looking at load, rep duration and rep velocity
For the slow eccentric phase, aim for an overload. So instead of deliberately moving a submaximal load slowly, create an overload and try to keep the weight up while going down. Here are some ways to do that:
Conclusion: when muscle growth (hypertrophy) is your goal, aim for a fast concentric movement with maximal intent. Use live velocity feedback to boost intent and to reach your velocity targets. To further increase muscle growth, aim for a slow eccentric movement. Do this with an eccentric overload instead of voluntarily lowering low weights slowly. Use live eccentric rep duration feedback to promote an extended eccentric time under tension.
When are fast reps better?
Spoiler: fast reps are often more effective than slow reps. Continue reading to discover why (and how you can leverage them to get even more bang for your buck).
Fast reps are better when you want to perform more repetitions, use more load or activate more muscle fibers.
As mentioned, scientific literature shows that fast reps enable you to do more reps (almost 2x more in this specific study!) or use more load. This increases the chance of muscle adaptation.
In addition to training loads, training volume, and rest intervals, movement tempo should be controlled and considered when planning and executing resistance-training programs. – Scientific source
Another benefit of using fast reps is that it activates more muscle fibers than slow reps.
The size principle from Dr. Henneman says that motor units are recruited in order of size from smallest to largest depending upon the intensity. In other words, low intensity repetitions like slow low-load reps, recruit mainly type I slow-twitch muscle fibers. High intensity repetitions like fast high-load reps recruit both type I and type II fast-twitch muscle fibers.
When more muscle fibers are recruited, you can expect a larger muscle adaptation.
The best way to promote fast repetitions – regardless of whether you’re lifting heavy or light weights – is by having live velocity feedback. In fact, there are several scientific papers showing that instant feedback from a VBT device can enhance velocity and power output by up to 10%. Especially when starting to fatigue, for example at the end of a set.
Learn more about the benefits of velocity based training via our free white paper:
Slow vs Fast reps for strength and power
We’ve talked about slow vs fast reps for muscle growth, but what about strength and power? Should you do fast or slow reps?
Fast concentric reps are better when strength or power is your goal.
As mentioned in the beginning of this article, with “fast reps” we mean reps performed with the intent to move the load as fast as possible. That doesn’t necessarily mean those reps are fast: lifting a 90% 1RM with maximal intent will not look like a fast rep. They are however always faster than a voluntary slow movement.
Literature shows that lifting with maximal intent results in significantly greater gains, compared to slower lifts:
| Half-maximal velocity | Maximal velocity | |
|---|---|---|
| Strength (1RM) | +9.7% | +18.2% |
| Velocity development | +10% | +20.8% |
| Time under tension (s) | 360.9 | 222.8 |
Both groups performed the same amount of sets and reps, using the same relative load (%1RM).
Even though the TUT of the half-maximal velocity group was 60% higher, the maximal velocity group showed almost 2x more strength gains! That’s why coach Travis Mash says:
“Instead of thinking about artificially increasing an athlete’s TUT for muscle hypertrophy, the better solution is to monitor eccentric and concentric velocities to ensure maximum effort and to compare rep velocity with target velocity.”
Travis Mash
We’ve created a power & strength training program that puts this theory into practice. You can use straightaway, while it also teaches you how to create any power or strength training program, using 3 core principles:
Conclusion: rephrasing the question
Unless you’re learning to coördinate a new movement, there is no reason why you should deliberately lift slowly. Yes, lifting slowly increases time under tension, but lifting fast increases (type II) muscle activation and performance: number of reps and load.
Therefore, you should always lift with maximal intent, especially when strength and power is your goal.
Assuming you do so, the question “How quickly should you move during resistance training?” is the same question as “Is it best to lift heavy or light”. After all, when lifting the load with maximal intent, the movement velocity is dictated by the load.
In the article Repetition Velocity: The Adaptation is in the Speeds, Travis Mash shares the adaptation from low velocity – high load strength training and compares it with the adaptations from high velocity – low load strength training.
By doing so, he dives deeper into the benefits of Velocity Based Training (VBT). Learn more about the basics of VBT and how many athletes and coaches implement it, via our free white paper:
FAQ
Make sure to always move faster than 10 seconds per repetition, during resistance training. Science shows that moving slower leads to inferior strength and muscle growth results.
Both fast and slow reps can help with losing weight. Slow controlled reps are good when you try to lose weight while getting familiar with the strength exercises. Fast reps are good for weight loss when you also want to become stronger.
The ideal strength training tempo takes 0.5 seconds to 8 seconds per repetition, but no longer than 10 seconds.
In strength training, tempo is often expressed in 4 digits: eccentric duration, pause, concentric duration, pause. E.g. 4020, which indicates a slow eccentric movement of 4s, no pauses, and a relatively faster concentric movement of 2s.
Here are two slow reps vs fast reps studies you should read:
– Maximal intended velocity training induces greater gains in bench press performance than deliberately slower half-velocity training
– The Influence of Movement Tempo During Resistance Training on Muscular Strength and Hypertrophy Responses: A Review
There is no scientific evidence that slow reps are better for muscle growth (hypertrophy). While it does increase time under tension, it also decreases the number of repetitions one is able to perform. Here’s whether you should use slow reps for hypertrophy.
Slow and controlled reps are better than fast and explosive reps, when you’re getting familiar with a strength exercise. Fast and explosive reps are better than slow and controlled reps when your goal is to increase strength and power.
Literature
A slow tempo decreases the maximum number of repetitions one is able to perform. Aim for a fast concentric phase and a slow eccentric phase.
- Wilk M, Zajac A, Tufano JJ. The Influence of Movement Tempo During Resistance Training on Muscular Strength and Hypertrophy Responses: A Review. Sports Med. 2021 Aug;51(8):1629-1650.
10s per repetition is inferior to faster reps, for muscle growth.
- Schoenfeld BJ, Ogborn DI, Krieger JW. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Med. 2015;45(4):577-585.
Slow reps increase time under tension, but decrease the number of repetitions in a set to failure. Fast reps enable you to do more reps or use more load.
- Wilk M, Golas A, Stastny P, Nawrocka M, Krzysztofik M, Zajac A. Does Tempo of Resistance Exercise Impact Training Volume? J Hum Kinet. 2018 Jun 13;62:241-250.
Instant velocity feedback can enhance velocity and power output by up to 10%.
- Weakley, Jonathon & Mann, Bryan & Banyard, Harry & McLaren, Shaun & Scott, Tannath & García Ramos, Amador. (2021). Velocity-Based Training: From Theory to Application. Strength and Conditioning Journal. 43. 31-49.
Lifting with maximal intent results in significantly greater gains, compared to slower lifts.
- González-Badillo JJ, Rodríguez-Rosell D, Sánchez-Medina L, Gorostiaga EM, Pareja-Blanco F. Maximal intended velocity training induces greater gains in bench press performance than deliberately slower half-velocity training. Eur J Sport Sci. 2014;14(8):772-781.
Loek Vossen
Human Movement Scientist | Marketing and Education
