What You Really Need to Understand About Lengthened Partials for Building Muscle

IF YOUR MEDIA diet puts you into certain corners of the muscle-obsessed fitness internet, you know about lengthened partials. If you don’t immediately recognize the term, we’ll get you up to speed: Lengthened partials are fractional reps performed with the target muscle in its stretched position. Good examples of this include the lower half of a pullup or biceps curl. Rather than raising the weight (or your body, in the case of the pullup) up through the exercise’s full range of motion, you’ll only go to about halfway to the top. Why? Muscle researchers have found that in many cases, those half-reps can still yield growth.

Anyone plugged-in enough to be familiar with the concept has also likely heard all kinds of wild theories about the protocol: Lengthened partials should be used for any and all exercises, no one should ever do a full rep ever again, your gains will jump by exponential degrees by using this one magic trick—the list goes on. There’s a lot of noise out there about this approach, and MH experts are trying to cut through it in our recent Strong Talk discussion.

“The problems with [the conversation around lengthened partials] right now is everyone’s trying to research every muscle,” said exercise physiologist and strength and conditioning coach Dr. Pat Davidson. Davidson was dismissive of some of the studies surrounding the protocol, as researchers seem to be approaching the topic both broadly in, terms of the muscle groups being tested, and with a limited scope of focus for the experiments. “They don’t give enough time and the stimulus is just kind of weird in some of these things. It’s going completely overboard.”

Does that mean that you should ignore everything you hear about lengthened partials and muscle building? Not quite, according to Davidson. There’s still solid research backing the use of the protocol in basic cases, and it’s not worth disregarding because the hype cycle is spinning out of control.

“There are some really good take-home points. When you stretch a muscle and challenge it, that’s probably the greatest threat you can put on it,” he said, calling back to another salient point in the conversation. “Most of the staple exercises that have been around for the test of time that everybody goes back to feature that naturally.”

Along with the isolation exercises mentioned above, he’s talking about compound movements like squats and bench presses, which apply heavy stimulus to the target muscles when they’re in the stretched position (the bottom of the squat and the bottom of the bench press, for example).

The real misread of the protocol would be performing your partials in the wrong place. If you’re hitting half-reps when the muscle is in the shortened position, you’re not coming close to doing enough to reap the benefits of your workout. “The things that most people do that never makes progress is they just do quarter squats at the top,” Davidson said. “They use too much weight, and they never go low enough… That’s not doing anything.” That applies to the other big compound movements, too; performing limited-ROM bench or leg press reps won’t get you anything but an empty ego boost.

The most important thing to remember is that the “lengthened” aspect is what’s important, not the “partial.” Davidson was clear about what it takes to really make this type of work useful: the hard stuff, i.e. taking the weight to that bottom portion of the movement, with the muscle in the lengthened position. You can’t completely skip out on ROM and expect muscle growth. “Versus somebody for real where it’s like boom, they bury that thing deep, they hold that stretch, and they drive out of that stretch,” he said, motioning through a bench press rep. “That’s the real deal.”

For more important lessons for growth, check out the MH Definitive Guide to Building More Muscle.