01:53 Slower eccentric? The stretch reflex
04:29 Review of 26 studies
06:35 Pearson et al. paper
How fast should you lift and lower your weights? A common idea in bodybuilding circles is that you should lower your weights with a 2 to 4 seconds eccentric tempo. This idea is not supported by science. In this video I explain what the optimum repetition tempo for maximum strength development and muscle hypertrophy is, according to the latest science. First, some terminology. When you lift a weight – a free weight at least that is called the concentric phase of movement. It’s when your muscles are shortening. When your muscles are lengthening under load. Typically when you are lowering a free weight, this is called the eccentric contraction or the eccentric phase of the movement. Also called the negative. We know that the eccentric phase of the movement is more important for muscle hypertrophy. If we look at studies directly comparing concentric vs eccentric lifting, we see that people actually tend to grow more muscle when they perform eccentric training.
And that’s because eccentrically muscles can produce more force. There may also be greater stretch mediated hypertrophy via titin mediated signaling where the muscle lengthens and titin is effectively spring loaded. So it makes sense. Intuitively, that performing a slower eccentric contraction enhances the eccentric and therefore enhances muscle growth. However, when we are deliberately slowing down how fast we lower the weight, this is not the same as actual eccentric overloading in research. Eccentric overloading in research requires lifting heavier loads, producing greater forces during the eccentric phase of the movement. So in these comparisons between eccentric and concentric studies, the eccentric groups are typically lifting higher loads because they can lower more weights than they can lift and therefore their muscles are subjected to higher tension. And it’s the higher tension that is driving the greater growth. If you are lowering the weight more slowly, you are not actually subjecting the muscle to more tension. You are subjecting it to more time under tension. However, the time under tension comes at the expense of being able to perform fewer repetitions. So this total volume is typically neutral. Moreover, part of the reason that you cannot perform as many repetitions with a slower eccentric as with a faster eccentric. So when you lower the weight more slowly, you become essentially weaker. Part of the reason for that is that you lose out on the stretch reflex. When you are lowering a weight and in general, when a muscle is stretching at a certain velocity, the muscle sends a signal to the brain. The brain registers this signal and the brain sends back a signal to very forcefully contract the muscle. When the muscle is contracting after a relatively fast eccentric movement when it’s lengthening under load at a certain speed, the brain essentially wants to prevent the muscle from tearing, and therefore it potentiates the signal in the muscle activity sent to the muscle, thereby enhancing how much you can lift.
The stretch reflex enhances muscle activity. if you’re performing a very slow eccentric, you lose out on that benefit of the stretch reflex. Moreover, during certain exercises, it may actually be very beneficial to have that stretch reflex because it may enhance stretch mediated hypertrophy. For example, let’s take a lateral raise or a lean-in lateral raise that I recently posted a video about. It’s when you’re performing a lateral race like this so that there’s still tension in the bottom position. Now, when you are lowering the weight relatively fast in the bottom position, if you are not letting the weight hit your legs, which you shouldn’t, because then you lose muscle tension you have to actively decelerate the weight and that requires high forces. So when you are lowering the weight faster compared to very slowly, you actually have extra emphasis on the bottom position. Because then in the bottom position, you have to fully decelerate the weight, re-accelerate it to initiate the next concentric action. So not only do you get a potentiating effect from the stretch reflex, you also get the benefit of having very high forces in the bottom position, which might enhance stretch mediated hypertrophy. So in the end, the seemingly obvious benefit of lowering the weight more slowly and emphasizing the concentric actually doesn’t translate into greater tension on the muscle, and it might actually reduce the amount of tension in the most important position, which is typically the bottom position when the muscle is most stretched and lengthened. Now this is all nice theoretically.
However, what does the actual empirical data say? We have a lot of studies on repetition tempo. Most of them don’t find significant differences between groups. For example, here’s a review of 26 studies. A recent review. They concluded the following: Completing eccentric tempos below 2 seconds increased subsequent concentric 1RM performance, velocity and power compared with greater than 4 seconds tempos. This is basically what I’ve been explaining. When you lower the weight more slowly, you lose out on a stretch reflex and generally performance goes down further. They concluded, quote: tempos above 4 second duration, increased time under tension, whereas reduced tempos allowed for greater volume to be completed. So this is what I was explaining, that there’s a trade off between – Yes, you are emphasizing time under tension with the slower eccentric, but this comes at the expense of lower total volume that is completed. They go on: Overall, evidence supports eccentric actions below 2 seconds duration to improve subsequent concentric performance. There is no clear difference between using eccentric tempos of 2 to 6 seconds. If the aim is to increase hypertrophic response and strength. So, they actually recommend decreasing the eccentric tempo to less than 2 seconds because research finds no significant differences in the vast majority of studies between different tempos with different eccentric durations. and we do know that you improve performance by not slowing down the eccentric too much. overall I think there is probably some benefit of slowing down the eccentric phase of the movement. It will increase time under tension during the most beneficial phase of the movement.
However, the benefit is probably very, very small because you’re not actually increasing how much weight there is. So there is no true eccentric overloading taking place. And in research we find that you need a lot of eccentric overloading. Minimum 20%, often 50% or so to actually get differences in muscle hypertrophy. This very small minor benefit is probably completely counteracted by the fact that you can produce fewer repetitions and you lose out on a stretch reflex. Possibly also losing out on some of the stretch mediated hypertrophy from decelerating the weight in a stretched lengthened position. So overall, you probably get a neutral effect, and indeed that is what we see in most studies. After this review was published, another recent paper came out, a randomized controlled trial by Pearson et al., and they confirmed the findings. They had strength trained men perform leg extensions with either a one or a three second eccentric duration. The researchers overall concluded: our results indicate that both repetition tempos produced similar muscular adaptations. So this again confirms that most research simply does not find significant differences, neither in strength development nor in muscle growth of different eccentric tempos. So overall, my conclusion for the eccentric is that it is important to retain muscular control. And if you’re doing an exercise like a lateral raise or a dumbbell curl, where there is otherwise no tension in the bottom position, it’s important to fully decelerate the weight using your muscles, not letting the weight freefall.
But then after the deceleration, quickly accelerating, going into the concentric. So it is very important to retain muscular control, but you don’t have to actively slow down the eccentric phase of the movement. Just make sure that your muscles are doing the work and you’re not letting the weights freefall. As for the concentric phase of movement, I think there is pretty much universal consensus that a fast explosive concentric or at least with the intent to be explosive and to push the weight up as fast as you can, as fast as it goes, because heavy weights will never go fast, even if you intend it to go fast, is best. It’s definitely best for strength development. Most of the research on that is very clear and in turn that might in the long run have a slightly beneficial effect on muscle hypertrophy, even though most studies, again don’t find significant differences between groups. Neither for the eccentric nor for the concentric duration, but we do know it’s better for strength development. We do know you can lift more weight and perform more volume when you do a faster concentric aiming to perform as many repetitions as possible. And if you’re aiming for strength development, even aiming to be very explosive to maximize muscle activity and really fully engage the nervous system which is beneficial to improve muscle coordination and improve the neural development that will make you stronger.
So retain control during your eccentric phases of movement. Generally don’t pause because you want to take advantage of the stretch reflex. Go straight into the concentric phase of movement. If your goal is muscle hypertrophy, just aim to complete as many repetitions as possible. If your goal is strength development, really aim to be explosive and maximize muscle activity during every concentric repetition. I think that summarizes the optimum repetition tempo for strength development and muscle hypertrophy.
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