We must first differentiate between slow eccentrics as a training tool/method and slow eccentric as a “style of lifting” for competitive performance.
Slow(er) eccentrics as a training method, which means that it isn’t the only style of lifting used and it is not the one used in competition, has many benefits.
In fact, with athletes that I train (and powerlifters) it typically represents around 1/3rd of their lifting volume.
For example, we might use my omni-contraction training system in which we have 3 whole-body workouts/week (only bg compound movements) and a 4th workout per week which is more bodybuilding/single joint exercises.
Of those three weekly workouts, one uses exclusively either slow eccentrics or eccentric overloads. A second workout use paused lifting (stato-dynamic) where you include 1-3 pauses during the eccentric phase of the lift and the third workout is regular lifting.
The benefits of a slow eccentric are mostly in the motor learning/injury prevention categories. A slower eccentric leads to a greater activation of the motor cortex, which favors motor learning and movement precision. But each repetition indeed becomes more neurologically demanding.
A slower eccentric (if it’s done with a high force production) also favors the development of the tendons as well as the distal parts of the muscle tissue (the portion of the muscles closer to the tendons), reducing the risk of tendon/muscle injuries.
On the downside, it does lead to more fatigue than a “normal” and “fast” eccentric, which can negatively affect concentric/lifting performance.
However, what I find is that this higher level of peripheral (muscle) fatigue will only affect lifting strength when the reps are higher than 3. For sets of 1 and 2 (maybe up to 3) as in typical max effort work, the impact of fatigue from the slow eccentric isn’t significant. YES, each slow eccentric is a bit more tiring, but it takes several reps to build up to a level significant enough to make a difference.
This reminds me of an IFBB pro bodybuilder that I trained; he would do his bench press sets with 180kg+ (for 6-8 reps), his first rep always used a slow eccentric and all of his reps after the first one used a normal-fast eccentric. This is just something he instinctively did… he thought the slow eccentric on the firs rep put him in the proper groove and he was able to speed up his eccentric after that.
Now, one drawback of a slow eccentric is that there will be a less powerful stretch reflex at the bottom of the repetition. Louie Simmons (RIP) had is lifters test various eccentric lowering speeds and he found that the faster the lifter went down, the faster they were able to lift the weight. That’s because a faster eccentric has an effect similar to plyometrics in that it builds more kinetic energy and activates a stronger stretch reflex. Both increase strength potential in the concentric (lifting) phase of the lift.
When top powerlifters were analyzed during competition, it was found that the best bench presser tended to lower the bar faster.
That doesn’t mean that switching to a fast eccentric will automatically make you lift more weight.
For one thing, a faster eccentric phase does increase the amount of force needed when you make the turnaround (switching from lowering to lifting the bar) as you must not only produce the force needed to lift the bar but also suddenly stop its descent.
There is also the danger of releasing muscle tension too much: when you lower the bar fast, you reduce intramuscular tension. If you release it too much, it can be harder to bring it back up. You might also decrease the tension in supportive muscles making you less stable, which will obviously make it harder to apply maximal force.
We can draw a parallel with depth jumps. Depth jumps work via the same mechanism as fast eccentrics: by increasing kinetic energy accumulation and the strength of the stretch reflex. (By the way depth jumps refer to standing on a box around 75cm high, stepping off and upon landing on the floor, jumping back up as high as possible).
Research has found that athletes who are highly trained in jumping exercises were POTENTIATED by the drop whereas athletes with less experience with jump training were INHIBITED.
It’s the same thing with fast eccentrics: if you are not well prepared and experienced with gradually faster eccentrics, doing fast eccentrics will. REDUCE your lifting performance, not increase it.
Also, when it comes to powerlifting performance we must consider two elements:
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A fast eccentric might be more beneficial for the squat than bench. Why? Because in the competition you must pause your bench press on the chest for 1-2 seconds (sometimes more depending on the judge), this pretty much nullifies the stretch reflex. This going down faster to create a stronger stretch reflex might be a wasted effort. There is no such rule on the squat where you can use a rebound in the bottom.
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A fast eccentric might be more beneficial/easier to use for those competing in “geared” (bench shirt and squat suit/tight knee wraps) divisions than those lifting “raw”.
Sorry for giving you such a complex answer, I wanted to be as thorough as possible.
But the take-home messages are:
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There is value in keeping some slow eccentric work in your program, but I wouldn’t do it on every single exercise or all the time.
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Using more of a “normal” eccentric speed on your bench and squat might be beneficial over going very slow. But going to a fast eccentric right away will surely be detrimental. So you might want to include some normal eccentric speeds (something like 2 seconds down) on your squats and bench. Maybe do the warm-ups and early sets with a slow eccentric and the rest with the normal speed.
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Even switching to a “normal” speed might be less effective at first, because your body is not used to that style of lifting. Give it 4 weeks then assess is you see a performance improvement from it.
