as you would do with a typical rep.
That means, for example, that you could use two hands to lift a dumbbell, then one hand to slowly lower it, while sacrificing little in the way of results. Focusing on the lowering – or the “eccentric” contraction – can lead to a more efficient gym session, Japanese researchers say.
In the study, published in the European Journal of Applied Physiology, researchers divided people into three groups of 14 for a 5-week, twice-weekly comparison.
One group performed dumbbell curls from full extension to about one-quarter of the way up, for 2 seconds up and 2 seconds down, in three sets of 10 reps. Another 14 people performed only the lift portion of the movement (a researcher helped them reset the weight after each rep), and another 14 did only the lowering part of the move.
The group that both lifted and lowered the weights increased the maximum force they could produce on a lift by 18% and increased the thickness of the biceps muscle by 11%.
The people who only lowered the weights nearly matched that, increasing their maximum force by 14% and muscle size by 10%. The lifting-only group increased their max force by 11%, while muscle size increase was insignificant.
Your muscle fibers work two ways. When you lift a dumbbell from a straight arm up to your shoulder, your biceps muscle is using a “concentric” contraction. As you lower that dumbbell back down, the biceps muscle is working to put the brakes on the descent – that’s called an “eccentric” contraction.
The lifting-plus-lowering group saw the biggest gains because they were pretty much doing twice the number of reps. The lowering-only group made similar improvements in strength and muscle with only half the work.
Study author Masatoshi Nakamura, PhD, a professor at Nishikyushu University, Japan, believes that eccentric muscle contractions produce greater neurological adaptations in the spine and brain than concentric contractions. In other words, your nerves learn to send more of the “pull harder” signal to your muscles.
At the same time, the spring action of a large protein called “titin” in the muscle fibers produces greater force during eccentric contractions while using less energy, and more titin could account for the increase in muscle size, which is called hypertrophy.
“Titin in the muscle fibers could be the best explanation for muscle hypertrophy,” Dr. Nakamura says. “However, we believe that other factors, such as neurological adaptations, also play a large role in increasing muscle strength.”
The short range of motion used in the dumbbell curls was an important factor. A study, published in the Journal of Strength and Conditioning Research, found that a partial range-of-motion triceps exercise produced greater muscle growth than full range-of-motion movements.
Although the people in this newest study only performed dumbbell curls, “we think the effect is similar in other muscles,” Dr. Nakamura says.
Your muscles are much stronger when lowering than they are lifting, so Dr. Nakamura suggests choosing a heavy weight to perform single-arm dumbbell curls. Use both arms to raise the dumbbell into the 50-degree position, then lower it over a 2-second count. For two-handed bent- or straight-bar curls, you can ask a spotter to help you lift the weights into position between slow lowering moves.
You can also try the same trick with leg curl or leg extension exercise machines, using two legs to lift the weight and allowing one leg to lower it.
In the near future, your gym might contain more equipment that was designed specifically around lowering movements.
“Other machines that can emphasize eccentric contraction are gradually being developed,” Dr. Nakamura says.
A version of this article first appeared on WebMD.com.