Slow lifting methods have been around since the early 1980's. Even today people are "rediscovering" the idea or trying to reinvent it using a slightly different format. But for the most part, this training strategy sucks. It sucked in 1983 and it sucks now.
Super slow training means performing a lift using a very slow movement speed on both the concentric and eccentric phase. Proponents generally recommend a tempo of 5 seconds for the concentric (lifting) and 5 seconds for the eccentric (lowering) phase, but some super slow coaches even recommend taking as much as 10 seconds to complete a single phase of the movement on each rep. And they recommend using this speed to take each set to failure.
Now, this training method has major drawbacks and I do NOT recommend it. But here's what fans of this method will tell you:
- When going to failure it doesn't matter what weight you're using. Even if you're using baby weights it doesn't matter since loading is irrelevant as long as you go to failure using the super-slow lifting speed.
- When lifting slowly during the concentric phase, you're minimizing momentum or even negating it completely. So muscle contraction must do all the work on every inch of every rep. Whereas when you try to accelerate the weight, momentum can reduce the muscle activity in later portions of the range of motion (since the load has momentum you don't need as much force to keep it moving up).
- When lowering the weight slowly, you activate mTor to a greater extent, which can be a potent activator of protein synthesis (muscle building).
- Very slow movements are safer because there's less force produced.
If the super slow method was effective, we'd see the results. By now it would've produced numbers of muscular and strong people. But we haven't heard from any of them because they don't exist. We simply don't see any very muscular or strong people who built their physique only using super slow training – at least nothing compared to what more traditional methods have produced. That said, in theory and if you look at lab studies, super slow training sounds promising. Yet it doesn't pan out in the real world.
1. It doesn't make you much stronger.
The same study showing that going to failure led to the same muscle mass increase regardless of the load also showed that strength gains with the lighter load were much lower. Now, call me old school but to become a lot bigger you need to also become a lot stronger. Of course, people on the low end of the muscular development scale might not need to increase strength a lot to gain some muscle, but to get really big you will have to move big weights.
I don't know any very muscular person who's not also strong. They might not be powerlifting strong, but they can move a good amount of weight. Once you already have a lot of muscle you might not need to keep training as heavy, but to go from small muscle mass to large muscle mass you will have to get a lot stronger.
Even when big strong guys back off the weight and opt for higher reps and more isolation work, their "lighter" weights are still pretty damn heavy. Recently, Paul Carter said he was doing just that. His definition of lighter weights? Over 400 pounds for barbell rows and 585 on the deadlift for fairly high reps.
Super slow proponents say that when you reach failure, regardless of the load used or speed of movement, you end up recruiting the fast-twitch (stronger) fibers too. So they argue that heavy lifting isn't more effective at making a muscle stronger since it doesn't recruit more muscle fibers.
In reality, fiber recruitment is only half of the battle, if that. The firing rate of muscle fibers is actually more important when trying to produce force. Firing rate means how frequently a muscle fiber "twitches" or contracts to produce force in a specific timeframe. And to train the capacity to have a high firing rate, you need to lift heavy or explosively – two things you don't find in slow training.
2. It minimizes force production.
Super slow means making acceleration as low as possible. And because you're moving so slowly, you're prevented from using heavy weights, which means low mass factor. So both the mass and acceleration factors are low, giving you quite possibly the lowest force output possible when lifting weights. It could be called "low force training" instead of super slow training.
What's the problem with low force? It means not recruiting the fast twitch, growth-prone fibers. But wait a minute. The super slow proponents say that when you reach failure you have full muscle fiber recruitment at the end of the set because your body must recruit more muscle fibers to compensate for the fatigued ones. And this is true. But for most of the set, until you've fatigued the fibers enough to be forced to recruit the fast-twitch fibers, you won't recruit these motor units that are the most prone to hypertrophy and getting you stronger.
Doing super slow reps to failure might allow you to recruit the fast twitch fibers for 1 or 2 reps out of your set, but when you're lifting heavier weights and focusing more on acceleration you're producing a lot more force, and will thus recruit those fast twitch fibers on pretty much all the reps.
And again, super slow will not improve firing rate. It might actually train you to use a low firing rate to do the job, which could make you weaker when trying to lift maximal weights or move explosively.
3. It will deplete muscle glycogen more than other types of lifting.
Glycogen begins to be used after about 12 seconds of intense effort. The longer a muscle must produce force, the more glycogen you use up. A slow set to failure might take you as much as two minutes to complete (although most of the time it is about 75-90 seconds). This will burn a boatload more glycogen than regular lifting.
Why is that important? Glycogen use and depletion raises AMPK which itself can inhibit mTor activation. MTor is basically the light switch that turns on protein synthesis. The more you deplete muscle glycogen, the more you risk inhibiting protein synthesis.
4. It's a mental battle on every set.
This form of training is hard to sustain in the long run. I like hard work as much as the next guy, but super slow reps to failure are excruciating. Trying to tolerate that pain can actually make you hate training. Loving your training and being motivated to do it is very important to get maximum results.
Many will fake themselves into hitting failure after a few weeks of super slow training, neglecting any results this method might give. Listen, a training session is not a test of mental toughness. There aren't points awarded for enduring the most discomfort. Only results matter. And it's hard to maintain a good focus for 90 seconds (or more) when doing one set of an exercise.
5. It's not really doable on the big lifts.
In fact, it's not doable on most free-weight movements. (It was originally designed to be used on machines.) Doing a super slow set of leg extensions to failure is one thing. It's uncomfortable but it's doable. Doing a super slow set of squats or deadlift to failure, well, that's not only two or three notches higher on the pain scale, it can actually be dangerous.
On these big lifts your posture is likely to fail way before the prime movers. You'll begin to lose body tightness and proper form on squats and deadlifts many reps before the legs and glutes are approaching failure.
This both makes these movements less effective because now you're forced to use light weights, but when you hit failure it's not even the failure of the muscles you're trying to build. So you have all the drawbacks with none of the theoretical benefits. And the fact that you're losing your tightness or proper lifting form can obviously lead to injuries.
Here's one instance in which you can use slow training effectively: when trying to improve mind-muscle connection with one specific muscle on an isolation exercise. In this case, it would be a temporary use because once you can feel the muscle working it wouldn't be necessary anymore.
It's dumb to purposefully try to lift weights while minimizing force production. There's no doubt that you can build a strong case for super slow training by quoting certain studies. But I trust real-world results more than isolated studies.