There is such a thing as lifting too light, though, which can affect just how beneficial your overall workout is. "If you aren't lifting heavy enough weights, your results—AKA your muscle strength and growth—will be suboptimal," says Brad Schoenfeld PhD, associate professor of exercise science at Lehman College in New York. In his research, he actually found that lifting at 20 percent of one repetition maximum (the highest amount of weight you can lift for one rep) produced not-so-great muscle growth when compared to lifting 40 percent and above. "Lighter load training in general, which is less than 70 percent of your one-rep maximum, produces lower increases in strength compared to heavier loads." That said, if you're working with a light load and want to see results, you've gotta up the reps.
Chief running officer of Run-Fit Jason Karp, PhD echoes this idea, stating that getting stronger is all about pushing yourself. "To improve muscular strength, the intensity of your workouts must be high," he says. "You have to work at the maximum or near maximum ability of your muscles to produce force, and that can happen only if your muscles contract against a heavy resistance."
"You have to work at the maximum or near maximum ability of your muscles to produce force, and that can happen only if your muscles contract against a heavy resistance." —Jason Karp, PhD
While there's no set way or a magic number that tells you if you're actually lifting too light, there are things to keep in mind when working with weights. "To improve your muscular strength, you need to either make your muscles bigger, or increase the ability of your central nervous system to 'communicate' with your muscles by increasing the number of muscle fibers it recruits and increasing the frequency of recruiting signals it sends to your fibers," says Dr. Karp.
To make your muscles bigger, you need a strong enough stimulus that leads to muscle protein breakdown, which leads to your muscles then repairing themselves for the better. What does that entail, exactly? "Lift a relatively heavy weight—about 80 to 85 percent of the maximum you can lift just once," he says, adding that you should just be sure to have enough recovery time between sets so that you can continue repeating the same intensity.
As far as improving the neural communication within your muscles, Dr. Karp says to lift weights that are roughly 95 percent of your max, but only do one to three reps per set. "When you train this way, you'll get a lot stronger without getting bigger muscles, because the total number of reps, and therefore the total amount of protein breakdown, is low," he says.
You can also do enough reps with your weights (not your heaviest) until muscle failure, though Dr. Schoenfeld says that from an increase of strength standpoint, "maximizing results requires the use of heavy loads." So... go hard or go home?
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