Switch up the speed of your reps to build muscle, functional fitness, and mind-body connection.
Time is a precious resource. When you have just one hour to spare, max, for your workout, it’s tempting to fly through the moves in your program.
In theory, it makes sense: You polish off more reps in less time, your heart rate spikes, and you might even tackle more exercises than you initially thought was doable. It has to be an efficient, effective method, right?
Not exactly. With every rep, your tempo matters more than you think, says Colin McGeen, the Personal Training Manager at Equinox Bloomfield Hills.
To understand why, you first need to know the three types of muscle contractions. There are concentric contractions, during which your working muscle is shortening to actively fight against and overcome a force. In an eccentric contraction, the working muscle is “lengthening” (read: returning to its resting length after shortening during the concentric phase) while contracting, and it's still producing force to slow down the load. There’s also an isometric contraction, during which the working muscle is neither visibly shortening nor lengthening. The force the muscle is producing matches the force it’s placed under, so there’s no joint action.
It’s easy to picture this during a biceps curl: You curl the dumbbells from your sides to your shoulders (the concentric phase), pause momentarily at the top (the isometric phase), and slowly lower the dumbbells back to the starting position (the eccentric phase).
For general muscle health, a moderate tempo is best practice; spend one to two seconds in the concentric phase and one to two seconds in the eccentric phase, with a slight pause in between the two, McGeen suggests. But intentionally adjusting movement tempo, slowing down or speeding up the eccentric and/or concentric phases, does have its benefits.
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Performing your reps in slow motion gives you the opportunity to ensure you’re activating the correct muscles and have the right movement mechanics, says McGeen. It allows you to establish better mind-muscle connection, whether you’re new to exercise as a whole or you’re new to a particular movement. “Once you've established that foundation, then it's a little bit more safe to start going into the faster movements,” says McGeen. “It's a great starting point to make sure we feel confident and comfortable in the movement. We're getting the right activation that we want to go for and actually connecting to the muscles working, versus just being, ‘Yeah, I feel something working. I don't know what it is.’”
Switching up your speed could also impact muscle growth. Research suggests that slowing down the eccentric phase of movement and speeding up the concentric phase is most ideal for muscle hypertrophy (with the caveat of requiring proper recovery), according to a 2021 Sports Medicine review. Although slowing down your eccentric tempo will likely reduce the number of reps you’re able to complete and potentially affect the maximum load you’re able to lift, it will also increase the amount of time your muscles are spending under tension. So long as you’re repping until you hit failure, that longer time under tension could provide enough stimulus to induce muscle growth — even with lighter loads, the researchers say.
This eccentric phase is where the magic happens, affirms McGeen. Eccentric contractions require less motor unit (a single motor neuron and the muscle fibers it stimulates) activation and use up less oxygen and energy to create the same force as concentric contractions, research suggests. And over time, eccentric contractions have been found to promote greater gains in strength, muscle mass, and neural adaptations. “If I'm doing 10 reps with an eccentric focus, it's almost the equivalency of doing 20 total reps with that exercise,” he explains. “So there is this really cool mechanical advantage that you can get out of it.” (Just know that eccentric exercise generates greater mechanical stress and tends to create more muscle damage, so recovery is key.)
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Still, there is a time and place for rapid-fire reps, says McGeen. Athletes, for instance, might do some of their training with lighter weights, focusing on moving it as quickly as possible to train speed and agility, he says. While there isn’t any specific tempo that’s studied to be more effective for building strength, faster resistance training is thought to provide a better stimulus for neural adaptations, which could ultimately lead to greater strength gains, according to the Sports Medicine review.
There’s a functional element, too, adds McGeen. “So if we’re looking at, ‘How quickly can I go from a dead stop to rapidly moving?’ you're going to really get a lot of nervous system activation,” he says. “You're going to train a lot more of your actual tendons and ligaments along the way. Training your tendons and ligaments in that fashion is also really, really good for more stability.” If you train your body to be able to move and react quickly, you’re better equipped to quickly activate the correct muscles when you, say, slip on an ice patch or stumble climbing up stairs. (Of course, you’ll need to pair this speed training with strength training so you’re physically strong enough to control your body’s momentum, he says.)
Switching up your training variables — whether it’s tempo, load, or volume — can be complicated, so chat with a Coach at your Club for personalized guidance. Regardless of your tempo, what matters most is moving with intention and control, truly focusing on mind-muscle connection. That, says McGeen, will have the biggest payoff.