When it comes to an effective muscle building workout, there are a number of factors to consider, including:
- Exercise selection
- Technique
- Relative effort (how hard you’re pushing your muscles to fatigue in a given set)
- Volume (number of “hard sets”)
- Rest periods
- Repetition tempo
This last variable (tempo) is one that is often overlooked, but how fast (or slow) you perform each repetition can impact your performance, risk of injury, and results.
Today, we’ll discuss slow reps vs fast reps, particularly as it relates to which are better for muscle growth (hypertrophy).
The 4 Phases of a Repetition
When it comes to performing an exercise you probably think of the lowering portion (eccentric) and the lifting portion (concentric). If you really want to dial down into the nitty gritty details, there are 4 components of a repetition:
- Speed of the eccentric phase (lengthening of the muscle)
- Duration of the pause at the “bottom” of the rep
- Speed of the concentric phase (shortening/contraction of the muscle)
- Duration of the “squeeze” at the top (the point of peak muscle contraction)
How these variables are manipulated impact time under tension (TUT), which is regarded by many as a key contributor to muscle growth. In other words, the more time a muscle is under tension, the more stress is applied across the muscle, which should bring about greater muscle growth).
Based on this line of thinking, longer eccentric and concentric phases should lead to better hypertrophy as these would, theoretically, result in greater times under tension.
Slow Reps vs Fast Reps: Research Findings
Interestingly, the research doesn’t pan out as you might expect. Super slow eccentrics and concentrics don’t necessarily lead to superior muscle growth compared to shorter lasting eccentrics and concentrics.
For example, going super slow on the eccentric phase (~10 seconds lowering) reduces the amount of total reps that you can do compared to doing a slightly “quicker” controlled eccentric (2-3 seconds lowering). Performing more repetitions with a quicker cadence would generally lead to the same amount of time under tension as performing a lesser number of super slow eccentric repetitions. Essentially, the argument in favor of super slow eccentrics for maximizing TUT goes out the window.
Additionally, research shows that individuals perform better and gain more strength doing quick/explosive concentrics compared to super slow concentrics.[1]
Another argument in favor of a faster concentric phase is that they provide a better stimulus for neural adaptations and greater strength gains. However, other research finds that for muscle growth, there’s not much difference in results for fast vs slow eccentrics (provided you’re taking the muscle to similar amounts of fatigue, i.e. proximity to failure).[2]
Still other studies indicate that controlled eccentrics may help promote muscular hypertrophy, indirectly affecting strength without adversely affecting neural adaptations.[3]
The takeaway here is that as long as you are controlling your reps and taking your muscles to the same point of fatigue (ideally 1-3 reps short of failure), muscle growth is comparable when performing slow or fast reps.
Slow Reps vs Fast Reps: A Few Considerations
New Exercise or History of Injury
Before we close the book on the slow reps vs fast reps for muscle growth, there are a few other considerations you may want to take into account.
If you’re someone rehabbing an injury or new to certain exercises, then performing slower eccentrics may help lower the risk of injury compared to letting gravity do the work for you while still offering similar results in muscle growth compared to quicker eccentrics.[4]
Practicality
Using super slow eccentrics and concentrics isn’t very practical as you’re more focused on counting how many seconds to take lowering/raising the weight instead of executing the exercise with good form and taking them to a high level of fatigue.
The Bottom Line on Slow Reps vs Fast Reps for Muscle Growth
Whether you choose slow reps or fast reps, the goal is the same -- take your muscles to a high level of fatigue (1-3 reps shy of failure). So, choose the rep speed that allows you to perform the greatest amount of high-quality reps as the overall amount of tension on the muscles is what will ultimately drive muscle growth.
An effective rep strategy could be:
- A controlled eccentric (2-3 seconds lowering)
- Not pausing in the bottom of the lift to take advantage of the stretch reflex which augments muscle activity and performance, leading to greater tension on the muscle.
- Explosive concentric to maximize neural adaptations and strength gains
- No pause at the top and repeat.
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References
- 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):772-81. doi: 10.1080/17461391.2014.905987. Epub 2014 Apr 15. PMID: 24734902.
- 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. doi: 10.1007/s40279-021-01465-2. Epub 2021 May 27. PMID: 34043184; PMCID: PMC8310485.
- Krzysztofik M, Wilk M, Wojdała G, Gołaś A. Maximizing Muscle Hypertrophy: A Systematic Review of Advanced Resistance Training Techniques and Methods. Int J Environ Res Public Health. 2019 Dec 4;16(24):4897. doi: 10.3390/ijerph16244897. PMID: 31817252; PMCID: PMC6950543.
- Pereira, P. E., Motoyama, Y., Esteves, G., Quinelato, W., Botter, L., Tanaka, K., & Azevedo, P. (2016).Resistance training with slow speed of movement is better for hypertrophy and muscle strength gains than fast speed of movement. International Journal of Applied Exercise Physiology, 5, 37–43.
