Lengthened Partials & Training at Long Muscle Lengths

A lengthened partial (LP) is a partial rep done only in the part of the range where the working muscle is stretched: the bottom half of a curl, calf raise or leg extension, or the stretched half of an overhead triceps extension. A shortened partial is the opposite, working only the half near full contraction (the "top half").

What the pooled evidence shows. Wolf et al. 2023 (Int J Strength Cond, 24 studies, Bayesian meta-analysis) compared partial with full range of motion:

• Overall, full ROM came out marginally ahead across outcomes. The difference was trivial to small (about 2.8% on average, 95% CI −1.7% to 7.4%).
• For muscle size overall, the difference was trivial (SMD 0.05).
• How the partial was done mattered. Partials at long muscle lengths showed a small edge over full ROM (SMD −0.28 in favour of partials; 95% CI −0.81 to 0.16, which crosses zero, so it isn't certain). Partials at short muscle lengths were trivially worse than full ROM (SMD 0.08).

The trials behind the hype, and who was in them. The eye-catching "partials beat full reps" results came from untrained participants doing a single exercise:

• Pedrosa et al. 2022 (Eur J Sport Sci): 45 untrained women on the leg extension. The stretched-half group (100°–65° knee flexion) gained more quadriceps cross-sectional area than full ROM at 50–70% of femur length.
• Kassiano et al. 2023 (J Strength Cond Res): 42 untrained young women on calf raises for 8 weeks (training status per the authors' 2026 review table). Stretched-half partials gave +15.2% medial gastrocnemius thickness, vs +6.7% for full ROM and +3.4% for top-half partials.

In trained lifters, it evened out. Wolf et al. 2025 (PeerJ) is a within-participant trial: 25 completers with 4.9 ± 4.1 years of training, one arm on LPs and the other on full ROM. They did an 8-week, 8-exercise upper-body program (chest press, rows, pulldowns, curls, triceps work), 4 sets to failure. Elbow flexor and extensor growth, and lat pulldown 10RM, were similar between arms, with point estimates near zero. Bayes factors of 0.16–0.3 gave moderate support for no difference. The authors' conclusion: emphasise the stretched position, "either by using a full ROM or LPs."

Calves may be a partial exception. Larsen et al. 2025 (Eur J Sport Sci, 23 trained lifters): stretched-half calf partials vs full ROM plus past-failure partials. The difference favoured stretched-half partials (+0.40 mm), but it was uncertain (95% CrI −0.06 to 0.85, BF 1.2, "anecdotal"). The gastrocnemius has repeatedly shown the biggest stretch effect.

The unifying idea. Training at longer muscle lengths tends to favour growth when there is meaningful external load at the stretch (Pedrosa, Pereira & Kassiano 2026 review). This is why exercise choice matters as much as rep range: an overhead triceps extension, a Bayesian cable curl or a deep-stretch calf raise loads the lengthened position, while some machines and exercises go slack there. A full ROM rep already includes the stretch. A lengthened partial isolates it. A top-half partial skips it.

Why it might work (mechanism, still uncertain). Some evidence suggests training at long lengths adds more longitudinal growth (fascicle length). A 2026 systematic review (Wolf et al., 8 studies, n=120) found muscle size and fascicle length increases may be greater with long-length training. But the evidence is "largely mixed", most fascicle estimates used methods of questionable validity, and no study has measured serial sarcomere changes directly (see You Can't 'Lengthen' a Muscle (the Toning Myth)).

Practical use.

• Default: full ROM, controlling the stretch rather than bouncing out of it.
• Lengthened partials are a legitimate alternative or add-on. Examples: when the shortened end of an exercise carries little load anyway, when a joint tolerates the top of a movement poorly, or as extra partial reps past failure in the stretched position.
• Avoid top-half-only partials as your main hypertrophy work. They're the variant the data don't support.
• Strength is specific to the trained range: 1RM gains tend to be biggest in the range you train (Principle of Specificity (SAID)). Lifters who need full-range strength should train full range.

• Lengthened partials ≈ full ROM for muscle growth in trained lifters (Wolf et al. 2025, n=25, BF 0.16–0.3 favouring no difference).
• Across 24 studies, partials at long muscle lengths showed a small, uncertain edge over full ROM (SMD −0.28, CI crossing zero). Partials at short lengths were trivially worse (Wolf et al. 2023).
• The biggest "partials win" results came from untrained women on single exercises (Pedrosa 2022 quads; Kassiano 2023 calves: +15.2% vs +6.7%).
• Calves show the strongest and most consistent stretch effect.
• The rule of thumb: don't skip the stretched part of the rep, and choose exercises that load it.
• Longitudinal growth as the mechanism is plausible but unproven (Wolf et al. 2026 review).