Lengthened partials: what they are and what the trials found

A lengthened partial is a rep that stays in the stretched part of the range: the bottom of a curl, the deep bend of a leg extension, the heel drop of a calf raise. You never go through the full movement. "Lengthened partials" is the gym name; in the papers it is partial range of motion training "at long muscle lengths". The reasoning behind it is that the muscle is loaded while it is stretched. The trials below test whether that shows up as more muscle than full reps.

This page covers what the trials compared, who they studied, where they disagree, and a practical way to try the method. It is a training page: if you have pain, an injury or a medical condition, talk to a doctor first. I'm a fitness coach, not a doctor.

What counts as a lengthened partial

Every exercise has a part where the working muscle is long and a part where it is short. In the trials, the lengthened part is the one studied. For example, the calf trial split the ankle's movement into a lengthened part, a shortened part and the full range,¹ and the knee-extension trial split the movement by knee angle.²

Which end is the stretched one depends on the exercise. On the leg extension it is the bent-knee end; on the preacher curl it is the nearly straight arm at the bottom.

What the trials measured

Eight trials and one meta-analysis are described here, with who was studied in each. Seven compared lengthened partials with full reps; the eighth compared the stretched half with the squeezed half. Most of the trials are small.

Three trials in women: more growth in some regions

• Knee extension, 45 untrained women. They were split into a control group and four exercise groups: full range, the bent-knee part, the straighter-knee part, and a varied-range group. The cross-sectional area of two quadriceps muscles (rectus femoris and vastus lateralis) was measured at four points along the thigh bone. The group training the bent-knee (initial) part had a greater relative increase than every other group at 70% of the thigh bone's length, and at 50% and 60% it beat the straighter-knee, full-range and control groups.² The result is regional: it does not say the whole thigh grew more.
• Preacher curls, 19 untrained young women. One arm trained the bottom (first) part of the range and the other the top (final) part, three times a week for 8 weeks. The bottom-part arm had a greater increase in biceps cross-sectional area at 70% of biceps length; this trial had no full-range group.³
• Calf raises, 42 young women. For 8 weeks, three times a week, they did 3 sets of 15 to 20 reps on a machine in the lengthened part, the shortened part or the full range. The medial (inner) calf muscle grew 15.2% with the lengthened part, 6.7% with the full range and 3.4% with the shortened part. The lateral (outer) calf muscle grew more with the lengthened part than with the shortened part (14.9% against 6.2%), but not clearly more than with the full range (7.3%, p = 0.060).¹

Five trials that found mostly similar growth

• Upper body, 30 trained adults (25 finished). One arm of each person was assigned to lengthened partials and the other to full reps. After 8 weeks of two sessions a week, muscle thickness changes in the elbow flexors and extensors were similar. The authors note the study may have recruited too small a sample to detect appreciable changes.⁴
• Preacher curls, 13 trained adults (11 men, 2 women). One arm did partials at long muscle lengths and the other full reps, five sets to failure, twice a week for 8 weeks. At 50% of the way along the upper arm, muscle thickness rose similarly; at 70% the partial arm showed a trivial to small edge. The authors say the small sample and the 8 weeks may have limited the result.⁵
• Leg press, leg extension and leg curl, 16 trained men. One leg trained with partials in the stretched part, the other with full reps, for 8 weeks. The cross-sectional area of the outer thigh muscle (vastus lateralis) on MRI rose by 9.3 cm² on average, with no evidence of a difference between legs. The authors call the study exploratory.⁶
• Knee extension, 45 people (the abstract does not give their training status). After 8 weeks, the thickness of the vastus lateralis (outer thigh) showed no differences between lengthened partials at 55% of the one-rep max and full range at 80% at any of the three sites measured. The authors conclude that lengthened partials at moderate load gave similar muscle growth to full range at high load.⁷
• Arm and thigh, 297 people at 15 sites. At the start, 163 were in the lengthened-partial condition and 134 in the full-range one; after 12 weeks, the authors describe the differences in arm and thigh muscle area as small and practically equivalent. Their formal equivalence tests (p = 0.071 for the arm and 0.019 for the thigh) did not clear the cutoff they had set, so they could not formally rule out an effect outside the smallest effect size of interest (±0.1).⁸

The pooled analysis

A 2023 meta-analysis looked at partial against full range of motion in general, across outcomes. It found a trivial overall difference that favored full range (a standardized difference of 0.12, 95% confidence interval -0.02 to 0.26). A subgroup of partial reps at long muscle lengths pointed the other way for muscle growth (-0.28, interval -0.81 to 0.16), but that interval is wide and includes zero, so it is a hint, not a result.⁹

Where the results disagree

The three trials in women measured more growth in some regions with the stretched part of the range, against the full range in two of them and against the squeezed part in the third.^2,1,3 The three trials in trained people and the knee-extension trial that set moderate-load partials against high-load full range measured mostly similar growth, and the largest trial found small differences the authors called practically equivalent.^4,5,6,7,8 The three trials in women are the ones that found more growth in some regions; the trials of similar growth used trained men, mixed groups, or (in two abstracts) people whose sex and training status are not given. The pooled analysis answers a different question, partial against full range in general: its overall difference was trivial and leaned toward full range, and its long-length growth subgroup leaned the other way with an interval that includes zero.⁹ The studies differ in who they trained, which muscle they measured, how long they ran and what loads they used, so they don't line up into one answer.

A strength trial went the other way: in 50 trained men, a 10-week bench press program at full range gave better neuromuscular results than the two-thirds or one-third range.¹⁰ That trial is about bench press strength, not growth at long muscle lengths, so it doesn't settle the growth question; keeping full reps in the plan is a practical choice.

The American College of Sports Medicine's 2026 position stand, in its review of reviews, says there were insufficient data to determine if muscle hypertrophy was influenced by range of motion. Its Table 4 counts one review with a positive effect on hypertrophy (n = 90) and three that could not determine an effect (n = 276).¹¹

How to try them

None of the trials says how many sets or reps to do, and they used different ones: 3 sets of 15 to 20 in the calf trial,¹ five sets to failure in the curl trial.⁵ The steps below are practical cues, not a prescription from a study.

1. Do the full reps first, through the whole range, as in your normal sets.
2. When full reps run out, keep going with reps in the stretched half of the range only, and stop when the reps stop being clean.
3. Pick exercises where the stretch is easy to load, and where setting the weight down is easy.
4. Start with one exercise and one set a session, and keep the rest of the week as it is.

How close to failure to take the set: reps in reserve. How much to lift as you progress: progressive overload. Slowing the rep down is a different lever: time under tension.

Common mistakes

• Replacing full reps with partials. The trials compared partials with full reps; they didn't test dropping full reps from your week (practical).
• Doing the shortened half instead. In the knee-extension trial, the group that trained the straighter-knee part had changes similar to the control group at 60% and 70% of the thigh bone's length.²
• Bouncing out of the bottom. If the weight bounces, it is too heavy for that range (practical).
• Calling a shallow squat a lengthened partial. A lengthened partial stays in the stretched part of a movement; a squat that stops high is a different thing (practical).
• Training through pain. If a position hurts, stop and ask a doctor or a physical therapist.

Common questions

What are lengthened partials?

Reps done only in the part of an exercise where the working muscle is stretched, such as the bottom half of a curl or a leg extension. Researchers call it partial range of motion training at long muscle lengths.

Do lengthened partials build more muscle than full reps?

The trials disagree. Three in women measured more growth in some regions,^2,1,3 and five in other groups of people measured similar growth.^4,5,6,7,8 The pooled analysis, which looked at partial against full range in general across outcomes, found a trivial overall difference favoring full range.⁹

Should beginners use lengthened partials?

Two trials describe their women as untrained: the 45-person knee-extension trial and the 19-person curl trial (in its methods); both measured regional differences.^2,3 Three trials used trained people,^4,5,6 and the rest don't say in their abstracts. Learn the full range first (practical).

How many sets of lengthened partials should I do?

The trials used different amounts, and none tested which amount is better. Start with one set on one exercise (practical), and count it toward your weekly total on the sets page.

If you'd rather have it built for you

A lengthened partial is one tool inside a week of training. Which exercises get one, and how heavy, are the parts a page can't settle. Coaching is the version where your workouts live in Trainerize, built around the days you actually have, and a weekly call goes over the week you just had and sets the next one. Coaching to build muscle explains how that works, and apply is where you tell me about your week.