For decades, exercise science held one dogma as sacred: full range of motion (ROM) is always superior. Anyone doing half reps was considered lazy or uninformed. But studies from 2023-2025 are fundamentally challenging this assumption — at least for a specific type of partial rep.
Lengthened partials — partial reps performed exclusively in the stretched phase of the range of motion — show comparable or even superior hypertrophy results compared to full ROM in recent research.
In a full ROM bicep curl, you move from a fully extended arm to complete flexion and back. In a lengthened partial, you only move from the extended position to the midpoint — the bottom half where the bicep is maximally stretched.
This technique builds on the concept of stretch-mediated hypertrophy: muscles grow particularly effectively when loaded in a stretched position. The mechanical tension in the lengthened position activates specific signaling pathways (mTOR, titin-mediated mechanoreception) that stimulate muscle growth.
The most comprehensive analysis comes from Wolf et al. (2023). This meta-analysis pooled multiple RCTs and reached a surprising conclusion: training in the stretched portion of ROM produces comparable or superior hypertrophy versus training through full ROM or in the shortened ROM.
Critically: exercises performed only in the shortened position (e.g., the top half of a curl) showed significantly less muscle growth. Where you train within the ROM makes the decisive difference.
The latest confirmation comes from a 2025 PeerJ study: in trained subjects, lengthened partial reps produced similar muscular adaptations to full ROM training. This is important because these results apply to experienced lifters, not just beginners.
One of the most influential individual studies: Pedrosa et al. (2022) compared training in the lower vs. upper ROM during preacher curls. The group training only in the stretched position showed greater bicep hypertrophy than the full-ROM group — despite using a smaller range of motion.
| Exercise | Lengthened Partial = Bottom Half | Effectiveness |
|---|---|---|
| Incline Dumbbell Curls | Extended arm to 90° flexion | Very high — biceps maximally stretched |
| Cable / DB Flyes | Wide position to midpoint | Very high — chest in stretch |
| Overhead Tricep Extension | Full stretch to 90° flexion | High — tricep long head stretched |
| Leg Extension (deep) | Bent knee to ~90° | High — rectus femoris stretched |
| Romanian Deadlift | Full stretch to half ascent | High — hamstrings maximally stretched |
Heavy compound movements like squats, bench press, and deadlifts are less ideal for lengthened partials because the stretched position is simultaneously the weakest and most injury-prone. Full ROM remains the safer and more effective choice here.
MUSCLE TECHNICS automatically prioritizes exercises with high tension in the stretched position — based on Pedrosa 2022 and Kassiano 2023. The AI coach selects the best exercises for your recovery status and equipment.
Try Free for 14 Days →Partial reps performed only in the stretched (bottom) phase of the range of motion. Recent studies show similar hypertrophy results to full ROM with less joint stress.
Not better, but comparable. Wolf et al. (2023) and the 2025 PeerJ study show similar muscle hypertrophy. Benefits: less joint stress and often less systemic fatigue.
Isolation exercises with high stretch tension: incline curls, flyes, overhead tricep extensions, deep leg extensions. Less suitable for heavy compounds like squats or deadlifts.
Master full ROM first. Then lengthened partials can be used as an advanced technique for breaking plateaus or managing joint issues.