Lengthened partials grew the quads just as well as full range of motion
In short
Sixteen men with about eight years of training trained twice a week for eight weeks, using lengthened partials on one leg and full range of motion on the other across leg press, leg extension and lying leg curl. Vastus lateralis cross-sectional area (summed over five MRI slices) rose by 9.3 cm² on average, and the difference between methods was -1.4 cm², which was not significant. Partials did not cost any growth, but squat and bench 1RMs still have to be tested through full competition range.
Lengthened partials, where you only work the stretched half of a movement, are often sold as superior to full reps. In this exploratory study of trained men, eight weeks of each method produced the same quad growth and the same fiber-level and cellular responses.
How was the study set up?
- Experiment 1: eight men averaging 5.6 years of training did leg extensions with each method. Vastus lateralis biopsies taken before, right after, and 3 and 24 hours later tracked gene expression and mTORC1 and Hippo signaling.
- Experiment 2: sixteen men averaging 8 years of training lifted twice a week for 8 weeks, one leg using full range of motion and the other lengthened partials, on leg press, leg extension and lying leg curl.
- Outcomes: vastus lateralis area summed across five MRI slices, plus fiber size, myonuclei, satellite cells and total RNA before and after.
Do partials build less muscle?
No. Vastus lateralis area grew by 9.3 cm² on average, and the partial-minus-full difference was -1.4 cm² (95% CI -6.1 to 3.8). Type I and II fiber size, myonuclei and satellite cell counts showed no meaningful differences either, and post-workout signaling changed over time with almost no difference between protocols. The flip side matters too: this study found no advantage for partials.
What does this mean for Big 3 training?
The trial covered machine lifts and one quad muscle. Treat lengthened partials as an option for accessories, or for working around a cranky joint. fairlift's Muscle Index is built on squat, bench press and deadlift 1RMs, so only log full-range lifts with legal depth and a chest touch as maxes, and keep partial sets out of estimated 1RM math. Check your score with the Muscle Index calculator.
The main experiment had only 16 men, and the authors describe it as exploratory. Whether women, beginners or upper-body muscles respond the same way is still unknown.
Frequently asked questions
What are lengthened partials?
Reps that only cover the part of the range where the muscle is most stretched. On a leg extension, that means moving through the deep-knee-bend half of the motion.
Do lengthened partials build more muscle than full range of motion?
In a study of 16 trained men over 8 weeks, vastus lateralis growth was the same with both methods. The difference was -1.4 cm² and not statistically significant.
Can a partial-range lift count toward a 1RM?
No. Squat, bench press and deadlift 1RMs used for the Muscle Index are only comparable when they meet a fixed depth and range of motion.
Which exercises did the study use?
Leg press, leg extension and lying leg curl, twice a week for 8 weeks. Barbell squats and bench presses were not included.
Source: PubMed