When you try to plan how to train a particular muscle group, there are a variety of techniques to choose from. Traditional sets, drop sets, super sets, giant sets, pyramid training, reverse pyramid, DogCrapp training, utilizing the stretch-shortening reflex, etc.
However, one variety that doesn’t get talked about as much is tempo.
Tempo used to be talked about a lot more back with the old school bodybuilders of the 70s and 80s; some would even claim that it was their secret weapon to growth.
Rep Tempo Role
While being a “secret weapon” might be a little bit extreme, tempo can be an important factor to make sure that you keep making progress. An easy example of this is when you observe people in the gym that are relatively new to lifting and do not have anyone to guide them. Far too often they put on a heavy weight on the bench press, barely struggle to get the bar to the top, and then almost nearly let the bar free-fall close to or onto their chest before trying to get another rep.
In essence, they are contracting pretty slowly on the concentric part of the lift (when the bar is going up) and relaxing way to quickly on the eccentric part of the lift (when the bar is going down). If you watch over a few months, you’ll notice that this type of lifter will not be making too much progress on the bench press.
Contrast this with an experienced lifter on the bench press going for a set of 10. You will see that they will lower the bar in a controlled manner (different lifters will use different speeds, but it will always be controlled) until the bar is barely above the chest, and then they will quickly contract and push the bar upwards at a faster speed at which it lowered. This is the first key point before we get into the nitty gritty part of this article:
The concentric phase should always have a faster speed than the eccentric phase.
If it doesn’t, then either the weight is too heavy for you, you need to fix your form, or you need to focus on controlling the weight down.
Eccentric Movement vs Concentric Movement
Now the big question is, why is the eccentric part of the lift so important and why does it matter so much that it be slower than the concentric phase? Furthermore, just how slow should the eccentric phase be?
First off, the eccentric part of the lift is the part where most of the damage occurs during each rep. Since damage is one of the stimuli responsible for muscle hypertrophy, the eccentric part of the lift actually creates a larger signal for muscle growth than the concentric part does given the same volume(1,2). Furthermore, the eccentric part of the lift stimulates loaded-stretch-induced prostaglandin release PGF-2alpha, which increases hypertrophy via multiple mechanisms(3,4,5).
Yet, if you let the weight drop too quickly then you will hardly be putting any force on the bar during the eccentric phase, thus negating an important half of each rep!
How Slow Is Super Slow Weight Training?
OK, so you should control the bar down, but how slowly?
While a recent and good review suggested that it really doesn’t matter how slowly you lower the bar as long as the entire repetition duration is between 0.5 and 8.0 seconds(6), there are a few limitations to this review that are important. The main one is that they did not distinguish between the concentric and eccentric part of the lift. Since the speed of these two phases should be thought of completely separately, this is an important limitation.
Theoretically, the concentric part of the rep should be quick. Actually, no study has ever shown that it should not be as quick as possible while maintaining good form and not using momentum. The more acceleration there is on the weight, the more force you are applying to the bar (remember from high school physics, F = m * a ??).
Thus, to generate a lot of force, and thus stimulate muscle fibers, you need both a heavy weight and a high acceleration.
If you are holding the weight still then you are only getting the acceleration due to gravity, but the faster you accelerate that weight, the more force there will be on your muscle fibers. (For example, if you are on a scale in an elevator, you will weigh just what you weigh due to gravity, but if the elevator accelerates up, then the scale will register that you weigh more because you are actually placing more force on the scale. Same concept.)
Lowering the Weight – Eccentric Phase
OK, so it makes sense to contract as fast as possible during the concentric phase in order to generate the most power and stimulate the most muscle fibers. What about the eccentric phase?
This force concept is almost reversed during the concentric phase. For example, the faster you push during the concentric phase, the more force you generate and the harder the rep is. However, the faster the weight moves during the eccentric phase, the less force you generate and the easier that part of the rep is. For example, if you move the weight as fast as it can (i.e. free fall) then you do not need to use any force until you “catch” it.
Thus, things need to slow down a bit during the eccentric phase.
The slower the lift, the more force on the bar.
If you are holding the bar sill, this is the maximum force that can be generated during the eccentric phase.
Ideal amount of time for super slow training?
However, it seems as though there comes a point of diminishing returns for how slow you can go. Once you get passed about four seconds or so on the eccentric phase of the lift, you start to make less gains. This is because you are fatiguing your muscles to the point where you are cutting in on your total volume. So while each rep does have more force, you will be able to get significantly less reps due to fatigue.
Also, the faster you lower the bar, the more damage occurs to your muscles, and the less quickly you recover back to full strength(7). Think about sprinting. If you are sprinting on a track and contract your hamstring while trying to lengthen it really quickly, you might pull it. That would be excessive damage but it still illustrates the point: the slower the eccentric, the less damage done. Going too fast might cause too much damage with not enough force, while going too slow might not cause enough damage to signal growth.
Yet, as long as you go fast on the concentric phase, you shouldn’t need to worry about lowering the weight too slowly on the eccentric part as long as you are under 4 seconds, which is much longer than what most people use.
In fact, it has recently been shown in rats that repeated bouts of fast eccentric contractions increased molecules related to muscle catabolism and decreased the muscle size (due to over-training – remember, high speed eccentrics increase damage and lengthen recovery) while the slow eccentric contractions did not increase these molecules but instead increased phosphorylated p70s6k by 227%, a marker related to muscle anabolism8. The fast speed was 180 degrees a second (about 0.83 seconds for the lowering portion of a bicep curl) while the slow was 30 degrees a second (about 5 seconds).
Tale of the Tape
However, with the data we have from human studies, 5 seconds would likely be too long for an eccentric contraction. With the data we currently have, stick with an eccentric speed of around 2-3 seconds. If you are not training very frequently and can thus utilize the extra muscle damage to build up more muscle, go ahead and make that speed a little faster, like 1 second.
If you are at an over-reaching phase or are training very frequently and need to recover soon, you would be better off sticking with a 3-4 second eccentric so that your strength does not decrease as much for the next session. It is very likely that using a mix of both methods would be superior to using only one of them exclusively. Also, as always, keep the concentric as fast as you can while maintaining proper form.