From Volume 5, Issue 8 of MASS
How Slow Should You Go?
by Michael C. Zourdos, Ph.D., CSCS
A new study says that deliberately slow eccentrics might be beneficial for hypertrophy. However, the totality of evidence on training tempo has a lot of holes in it. This article takes a thorough look at both concentric and eccentric durations for strength and hypertrophy.
Study Reviewed: Effect of Different Eccentric Tempos on Hypertrophy and Strength of the Lower Limbs. Azevedo et al. (2023)
- Eight men and two women who hadn’t lifted for at least three months performed the leg extension with a 2-second (eccentric): 1-second (concentric) tempo on one leg while the other leg used a tempo of 4:1 for eight weeks.
- Researchers reported no statistically significant differences for strength gains or vastus lateralis muscle growth. However, small effect sizes favored the 4-second eccentric condition for hypertrophy of the rectus femoris and vastus medialis.
- Overall, the body of literature surrounding rep tempo is largely based on untrained subjects and training protocols which leave a lot to be desired. This article breaks down the literature to provide rep duration takeaways for both hypertrophy and strength goals.
The presently reviewed study from Azevedo (1) used a within-subjects design on the leg extension. 10 untrained individuals (8 men and 2 women) performed unilateral leg extensions twice per week on each leg. One leg trained with a 4-second eccentric and one used a 2-second eccentric, with the concentric standardized to 1-second in duration in each condition. The change in one-repetition maximum (1RM) leg extension strength was similar between conditions. However, small effect sizes for muscle thickness changes in the rectus femoris and vastus lateralis favored the 4-second duration. These results suggest that a 4-second eccentric duration may have a slight advantage for hypertrophy over a 2-second duration in untrained individuals. However, with conflicting data on the topic, we must explore various avenues to interpret these findings. Therefore, this article will discuss:
- Eccentric duration, volume, and time under tension.
- How appropriate eccentric duration may be specific to exercise selection and training status.
- Why future research should not control for concentric duration.
- The importance of individualizing eccentric duration.
Purpose and Hypotheses
The purpose of the reviewed study was to compare changes in quad hypertrophy and strength gains following eight weeks of leg extension training using either 2- or 4-second eccentrics in untrained men and women.
The researchers hypothesized that there would be greater hypertrophy and strength changes with a 4-second versus a 2-second eccentric duration.
Subjects and Methods
10 untrained men (n = 8) and women (n = 2) participated. The available subject details are in Table 1.
The presently reviewed study used a within-subjects design. Specifically, the 10 subjects trained unilateral leg extensions twice per week with at least 72 hours between sessions on each leg. One leg used a 2-second eccentric and the other leg a 4-second eccentric on all repetitions. All subjects were right leg dominant; thus, the researchers assigned 50% of right legs to one condition and 50% of right legs to the other condition. The concentric phase was standardized to 1-second in duration, with 0 seconds between the eccentric and concentric in both conditions. A metronome controlled lifting duration. For the training program, subjects performed five sets to failure at 70% of 1RM with three minutes of rest between sets in both conditions during each session. The leg (4-second or 2-second) that was trained first in each session was alternated.
The researchers reported time under tension and total repetitions performed during the training program. In addition, before and after the training intervention, researchers assessed leg extension 1RM and muscle thickness of the quads (rectus femoris, vastus lateralis, and vastus medialis) using ultrasonography. Importantly, only the concentric portion of the movement was performed during the 1RM tests, and researchers did not control rep duration during testing.
Time Under Tension and Reps Performed
Time under tension was significantly greater (p < 0.001, +48.71%) in the 4-second versus the 2-second condition (Figure 1); however, average reps performed throughout the entire eight weeks were similar between conditions (p = 0.75) (Figure 2).
Strength and Hypertrophy
Vastus medialis muscle thickness increased significantly more (p = 0.018) in the 4-second eccentric condition than the 2-second eccentric condition. There were no other significant differences between groups. There was also a small effect size for rectus femoris muscle thickness in favor of the 4-second condition; however, given the small sample size and lack of significant difference, we can’t be confident that this finding is meaningful. Table 2 shows the means, standard deviations, and between-group effect sizes for all outcomes.
The presently reviewed study (1) suggests that training with a 2- or 4-second eccentric tempo on the leg extension isn’t consequential for strength, but training with a 4-second eccentric tempo may provide a small hypertrophic benefit in some quad muscles. However, there are conflicting results in the existing literature on eccentric duration and hypertrophy. Further, many studies to date have used untrained individuals and poor training protocols. Therefore, in addition to reviewing the current study, this interpretation section will thoroughly cover the literature on eccentric duration, examine the importance of concentric velocity, and discuss what I believe is the most overlooked factor in this area of research: individualizing eccentric duration.
Longitudinal Literature Review
There are two meta-analyses, a systematic review, and a brand new comprehensive review on movement tempo to help illustrate the state of the literature. Let’s briefly review those papers, which are from Schoenfeld et al (2), Hackett et al (3), Davies et al (4), and Wilk et al (7). Schoenfeld and Hackett examined repetition duration and hypertrophy, Davies analyzed rep duration and strength outcomes, and Wilk tackled rep duration on both hypertrophy and strength.
Schoenfeld et al 2015 (2): This meta-analysis aimed to determine the effect of total movement duration (eccentric and concentric) on muscle hypertrophy. The meta-analysis concluded that a wide range of repetition durations – 0.5 to 8 seconds – could maximize muscle growth, with durations of ≥10 seconds providing slower rates of muscle growth, on average. However, this meta-analysis only included eight studies, and all of them were in untrained individuals; thus, it’s difficult to make definitive conclusions from the Schoenfeld meta.
Davies et al 2017 (3): Davies analyzed 15 studies that looked at concentric and eccentric duration for strength gain. Specifically, the 15 studies were classified as fast, which was a 1-second concentric (or maximal intended concentric) and 1-second eccentric (1:1) or moderate-slow, in which the exercise was performed at least at a 2:2 duration (and in some cases slower). Overall, the fast durations tended to produce better strength outcomes, which was supported by a 0.31 effect size in its favor compared to both moderate and slow durations combined.
Hackett et al 2018 (4): Similar to Schoenfeld, Hackett evaluated the effect of rep duration on hypertrophy, but Hackett’s meta-analysis only included six studies due to stricter inclusion criteria. Five of the studies examined quadriceps hypertrophy, with two studies assessing biceps growth. Hackett classified duration as “fast” if the total rep duration was ≤2 seconds and “moderate-slow” if the entire duration was ≥2 seconds. Three studies found significantly more growth for quads with a moderate-slow duration, one study favored fast training, and the other reported no group differences. Interestingly, both studies examining the biceps found significantly greater growth with fast training.
Wilk et al 2021 (7): This review provided the general conclusion that hypertrophy is not enhanced by either slow or fast movements. Then, the authors went on to state that a controlled eccentric followed by a faster concentric is recommended, but the researchers avoided recommending specific rep tempos. The authors also explain that while slower eccentrics increase time under tension, this effect often leads to lower total training volume, suggesting more than one tempo strategy to maximize hypertrophy.
The most evident finding from the meta-analyses and reviews is that the concentric phase should be fast or performed at a maximal intended velocity to maximize strength gains. For hypertrophy, the findings suggest that lifters are probably fine with any reasonably controlled eccentric as long as it’s not excessively slow. However, individual studies from the Hackett systematic review warrant closer inspection. For example, Tanimoto and Ishii (8) found significantly greater increases in quad cross-sectional area in a group of untrained older men performing leg extensions with a slow eccentric tempo (3:1) versus a fast tempo (1:1). Although both groups trained at 50% of 1RM, the slow tempo group trained to failure while the fast tempo group only performed eight reps per set, which is likely an inferior stimulus. Further, this study also employed a third group that performed three sets to failure with a 1:1 tempo at 80% of 1RM, and that group increased cross-sectional area to a similar degree as the slow tempo group. Two other studies from Watanabe et al (9, 10) both reported greater improvement in quad cross-sectional area with a 3:3 cadence on the leg extension versus a 1:1 cadence training over 10 weeks. However, one study had both groups perform 3 × 8 at 50% of 1RM (9), and the other had both groups perform 3 × 13 at 30% of 1RM (10). Therefore, the slower cadence made for a more difficult workout and potentially better stimulus (i.e., possibly greater metabolic fatigue, lower reps in reserve, increased mechanical tension) as 8 and 13 reps at 50% and 30% of 1RM, respectively, aren’t incredibly taxing. Therefore, when considering the studies from the Hackett systematic review used to support a slower cadence for hypertrophy, it seems that we can explain those findings by critiquing the study design or the participant characteristics (untrained and older adults aged 59-77 yrs). Table 3 summarizes the conclusions of the aforementioned meta-analyses and systematic reviews.
Placing the Currently Reviewed Study into Context
In general, the present results show similar adaptations between a 2- and 4-second eccentric duration on the leg extension, with a lean toward the 4-second duration for growth of some quad muscles. While I’d typically expect enhanced strength with a 2- versus 4-second eccentric duration, the load remained the same throughout the entire protocol (i.e., 70% of 1RM) in the presently reviewed study, and reps performed weren’t different between conditions. Two recent studies, not included in the meta-analyses or the systematic review, from Assis-Pereira et al (5) and Shibata et al (6), don’t help clarify the hypertrophy picture. Assis-Pereira (5) reported 10.30% more biceps growth in a group training the preacher curl with a 4:1 cadence versus a 1:1 cadence. That’s a large group difference, and the authors of the presently reviewed study speculate (and I agree) that a 1-second eccentric may be too fast on a preacher curl to resist gravity, which could compromise both the eccentric tension and subsequently the stretch-reflex. Shibata (6) found that collegiate soccer players training the squat twice per week with 3 × failure at 75% of 1RM experienced greater strength gains with 2:2 training versus 4:2 training, but with a similar rate of quad muscle growth between groups. The similar rate of growth in Shibata is despite the 2:2 group performing, on average, three more reps per set than the 4:2 group.
When considering all of the evidence, it’s tough to draw a firm conclusion on the present study’s hypertrophy findings. However, it’s worth considering that a single-joint, machine-based movement, which requires little skill, might be a better candidate for slower eccentrics than a skill-based movement such as a squat. In addition to the presently reviewed study finding a 4-second eccentric to produce slightly greater hypertrophy on the leg extension exercise, all other studies reporting greater hypertrophy with deliberately slow eccentrics have employed a single-joint exercise (usually the leg extension). However, studies using squats have reported either no difference between fast and slow eccentrics (6, 11) or an enhanced rate of muscle growth with fast eccentrics (12). Therefore, based on the evidence’s totality, any additional hypertrophic benefit to slow eccentrics might be relegated to lower body single-joint movements.
Before continuing with a more in-depth discussion of the concentric phase and individualization of eccentric duration, I want to pause for a moment and clarify that slow eccentrics might be beneficial for managing pain or returning to training from an injury. Slow eccentrics or tempo training (i.e., 3:3 or 5:2) cause an athlete to use a lower load, which may prevent an individual from progressing too quickly or help someone manage pain symptoms when returning to train after an injury-related layoff. While a deep discussion of this topic is outside the scope of this article, it’s important to note that slow eccentric durations or total tempos may be programmed for various exercises for pain considerations. This interpretation is independent of those considerations.
Typically, longitudinal studies carry the most weight when determining how to implement research into training. While that’s good policy, this interpretation has poked holes in the tempo training literature. Specifically, most studies are in untrained individuals, protocols have been too easy in the “fast” tempo group, or a fast cadence has been too fast to maximize the stretch reflex. Please see here and here for in-depth discussion of stretch reflex physiology. In short, when muscles are acutely lengthened (this happens during the eccentric phase), there is a recoil as you transition to the concentric. Therefore, the stretch reflex is why preceding the concentric phase with the eccentric phase makes you stronger than performing the concentric alone. Nonetheless, due to the aforementioned holes in the literature, we can turn to some acute data. First, it’s essential to note that most of the research referenced so far has controlled concentric cadence as well as eccentric cadence. However, there doesn’t seem to be merit to performing a deliberately slow concentric; thus, if training for performance, the goal of the eccentric should be to maximize the concentric. Various acute studies from Wilk et al have shown slow eccentrics to compromise concentric velocity or 1RM. Specifically, Wilk found a 2-second eccentric on the bench press to produce greater concentric velocity at 70% of 1RM on the bench press than a 6-second eccentric (13) and a 2-second eccentric to lead to a greater 1RM than a 5-second or 10-second eccentric (14) in crossover design studies. Further, Norbega et al (15 – MASS Review) reported that a 2:2 tempo on the leg press resulted in 10 fewer reps over three sets to failure at 80% of 1RM on the leg press versus a self-selected rep duration. Similarly, Van den Tillaar (16) found that when lifters deliberately slowed their eccentric (no specific duration, just “slower” than normal) concentric peak velocity and power were decreased during a 4RM squat compared to a preferred eccentric duration. Subjects in the Wilk studies and Norbega’s self-selected condition performed the concentric phase at a maximal intended velocity; thus, relatively faster eccentrics maximized performance of the concentric phase. Turning our attention back to the longitudinal literature, a frequently cited study from Gonzalez-Badillo et al (17) supports using maximal intended concentric velocity. Specifically, that study found that lifters gained strength at roughly a 100% greater rate when training the concentric phase of the bench press with maximal intended concentric velocity (+18.2%) versus deliberately training it with half of their max velocity (+9.7%). In the Gonzalez-Badillo study, time under tension was greater in the half velocity group, and researchers controlled eccentric duration in both groups to 0.30-0.50 m/s in both groups. Based upon research by Carzoli et al (18), which established normative eccentric durations (more on Carzoli in a moment), the Gonzalez-Badillo participants’ eccentrics were probably a bit slow. Still, overall the collection of studies in this paragraph shows that deliberately slowing the eccentric too much compromises the concentric phase. Further, deliberately slowing the concentric phase can attenuate strength gains. So, for strength purposes, it makes sense to ensure maximal concentric performance, which first requires an ideal eccentric phase.
Suppose we accept the premise that for strength gain, or at least for acute performance, the goal of the eccentric is to enhance the concentric. In that case, research should aim to individualize eccentric duration. If you have a 6’4” and a 5’5” lifter, their normative eccentric durations on squats won’t be the same. In other words, a “fast” duration of 1-second may be acceptable for the 5’5” individual, but fast might actually be 1.5 or 2 seconds for the 6’4” person. Carzoli et al (18) found that, on average, speeding up a person’s normative (i.e., typical) eccentric duration (0.75 times normative) resulted in faster concentric velocity during a single repetition set at 60 and 80% of 1RM on the squat and bench press in trained lifters compared to someone’s normal eccentric speed or a deliberately slow (2 times normative) speed. In other words, if a lifter’s normative eccentric squat duration was 1.5 seconds, then speeding up their descent to 1.125 seconds tended to result in a faster concentric than both a 1.5-second duration and a slower 3-second duration. The subject characteristics and normative eccentric durations from Carzoli are listed in Tables 4 and 5, respectively. Importantly, rep duration should be individualized, but these lifters were reasonably well-trained; thus, the durations in Table 4 may be applicable if you have similar proportions to the study’s lifters. Also, normative duration (and hence the fast duration) differed between the squat and bench press, and durations tended to slow as barbell load increased, demonstrating that the ideal eccentric durations are both exercise- and load-specific.
Lastly, the above isn’t to unequivocally say that you should speed up your descent on squats and bench presses; rather, if your normative duration is similar to or slower than those seen in Table 4, and you fit the study’s lifter profile, speeding up your eccentrics a bit might be worth a shot. On the other hand, some lifters already have fast eccentrics, and thus shouldn’t speed up their descent. In other words, if you’re attempting to maximize concentric performance with the eccentric, then you need to figure out what the right eccentric duration is for you.
As this article concludes, it’s crucial to recognize that eccentric duration is not a one-size-fits-all concept. Instead, it’s dependent on various factors including (but likely not limited to) the following:
- The specific exercise.
- The lifter’s goal (i.e., strength, hypertrophy, athletic performance, injury recovery, pain management, etc.).
- The lifter’s proportions (i.e., height, femur length, humerus length, etc.).
For strength, it seems to make sense to use the eccentric as a way to enhance the concentric. For hypertrophy, the data are less clear; however, there’s probably a little more leeway. On skilled movements such as the squat, I’d probably avoid deliberately slow eccentrics unless you’re using them for pain management purposes. For movements such as the leg extension, an intentionally slow eccentric up to around 2-3 seconds is probably fine and may enhance muscle growth, but the jury is still out.
Next, a longitudinal study that individualizes eccentric durations but instructs maximal intended velocity on the concentric of the squat and bench press would be ideal. Per Carzoli et al (18), one group could train at their normative eccentric duration, another at a fast duration (0.75 times the duration), and another at a slow eccentric duration (double the descent time).
Applications and Takeaways
- The currently reviewed study (1) found that leg extension 1RM was unaffected by rep cadence, but hypertrophy of some muscles leaned in favor of a slower eccentric.
- Notably, this study didn’t find a difference in the number of reps performed; thus, intentionally slow eccentrics may be acceptable for hypertrophy purposes on specific movements when volume is not compromised.
- For strength, the goal of the eccentric phase is to maximize the concentric. I see nothing wrong with using the eccentric to enhance concentric performance for hypertrophy as well, especially on skilled exercises. However, that doesn’t mean everyone needs to speed up their eccentric. A controlled eccentric, even if slower than a duration that maximizes the stretch reflex, should suffice for hypertrophy.
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