Hypertrophy
Systematic Review
2023
Partial Range of Motion Training Elicits Favorable Improvements in Muscular Adaptations When Carried Out at Long Muscle Lengths
By Max Wolf, Alec Androulakis-Korakakis, Fisher James, James Steele and Brad J. Schoenfeld
European Journal of Sport Science, 23(8), pp. 1474-1485
<h2>Abstract</h2>
<p>The use of partial <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="range of motion">range of motion</a> (ROM) repetitions in resistance training has historically been discouraged in favor of full ROM training, on the basis that incomplete joint excursion reduces the overall mechanical stimulus and limits hypertrophic potential. However, emerging evidence suggests that this blanket recommendation fails to account for an important distinction: the region of the ROM in which partial repetitions are performed. When partial repetitions are executed in the portion of the movement where the target muscle is maximally elongated—the lengthened position—rather than the shortened position, qualitatively distinct and potentially superior adaptive responses may occur.</p>
<p>The present <a href="/terms/systematic-review/" class="term-link" data-slug="systematic-review" title="systematic review">systematic review</a> synthesized evidence from controlled resistance training studies comparing partial ROM training at long versus short muscle lengths, and where available, partial ROM training at long muscle lengths versus full ROM training. Outcomes included morphological measures of <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> (muscle thickness, <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="CSA">CSA</a>, volume) and, in some studies, muscle architectural indices.</p>
<p>Results consistently indicated that partial repetitions performed at long muscle lengths produced significantly greater hypertrophy than partial repetitions at short muscle lengths, and in several studies were comparable to or superior to full ROM training. These findings are mechanistically consistent with the growing <a href="/terms/stretch-mediated-hypertrophy/" class="term-link" data-slug="stretch-mediated-hypertrophy" title="stretch-mediated hypertrophy">stretch-mediated hypertrophy</a> literature and suggest that the position-specificity of loading is more important than ROM completeness per se. Practical implications include the targeted use of lengthened-position partial repetitions for hypertrophy optimization, particularly in exercise programming where time efficiency is prioritized [1].</p>
<h2>Introduction</h2>
<p>The question of how much of a joint's available <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="range of motion">range of motion</a> should be utilized during resistance exercise has practical and scientific relevance for both <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> and injury prevention. Conventional training guidance has long advocated for full ROM training on the grounds that it maximizes the total mechanical work performed by the target muscle, engages the muscle across its entire length-tension relationship, and prevents the adaptive shortening associated with chronic training through restricted ROMs. While this rationale is broadly sound, it conflates the total range traversed with the functional position of loading, overlooking the possibility that different portions of the ROM may contribute differentially to hypertrophic adaptation [1].</p>
<p>The integration of <a href="/terms/stretch-mediated-hypertrophy/" class="term-link" data-slug="stretch-mediated-hypertrophy" title="stretch-mediated hypertrophy">stretch-mediated hypertrophy</a> research has provided a mechanistic framework for re-evaluating partial ROM training. As reviewed comprehensively by Maeo et al. [2] and others, muscles loaded at long lengths (i.e., in the stretched position) appear to receive a disproportionately potent hypertrophic stimulus compared with muscles loaded in the shortened position at equivalent volumes and intensities. This finding raises the possibility that a partial repetition performed exclusively in the stretched region of a movement—a "lengthened partial rep"—might elicit hypertrophic responses comparable to or exceeding those produced by full ROM training, given that the full ROM includes both lengthened and shortened loading phases.</p>
<p>For example, in a conventional barbell curl, the biceps brachii is maximally elongated when the elbow is nearly fully extended (the bottom of the movement) and maximally shortened at the top of the curl. A lengthened partial rep would restrict the repetition to the lower 30–50% of the curl's ROM where the biceps is most stretched. Conversely, a shortened partial rep would restrict the repetition to the top portion of the movement. <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="If">If</a> <a href="/terms/lengthened-partial-repetitions/" class="term-link" data-slug="lengthened-partial-repetitions" title="lengthened partials">lengthened partials</a> are superior to both shortened partials and potentially comparable to full ROM training, this has significant implications for exercise selection, programming, and our mechanistic understanding of resistance exercise-induced hypertrophy [3].</p>
<p>This <a href="/terms/systematic-review/" class="term-link" data-slug="systematic-review" title="systematic review">systematic review</a> was designed to critically evaluate the available controlled evidence on this question, synthesizing data from studies directly comparing partial ROM training at different positions within the range of motion and comparing lengthened partials with full ROM training conditions.</p>
<h2>Methods</h2>
<h3>Search Strategy</h3>
<p>A systematic search was conducted in PubMed/MEDLINE, EMBASE, SPORTDiscus, and Web of Science using combinations of the following terms: "partial <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="range of motion">range of motion</a>," "partial repetition," "lengthened partial," "shortened partial," "long muscle length," "short muscle length," "stretched position," "full range of motion," "<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a>," "muscle thickness," "<a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a>," and "resistance training." No date restrictions were applied. In addition to database searches, reference lists of included studies and relevant reviews were hand-searched, and forward citation searching was performed for key included studies.</p>
<h3>Inclusion and Exclusion Criteria</h3>
<p>Studies were eligible for inclusion <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> they: (a) were original peer-reviewed research using a controlled experimental design (randomized or quasi-randomized); (b) compared at least two conditions differing in the position of ROM in which partial repetitions were performed (lengthened vs. shortened), or compared <a href="/terms/lengthened-partial-repetitions/" class="term-link" data-slug="lengthened-partial-repetitions" title="lengthened partial repetitions">lengthened partial repetitions</a> with full ROM training; (c) involved human participants performing a resistance training program of at least four weeks duration; (d) assessed muscle morphological outcomes (CSA, thickness, volume, or fascicle length) using validated imaging methods; and (e) provided data sufficient for qualitative synthesis and, where applicable, <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> computation. Studies assessing acute responses only, animal studies, and studies without direct comparison of ROM position conditions were excluded.</p>
<h3>Data Extraction and Synthesis</h3>
<p>Two reviewers independently extracted study design, participant characteristics, exercise performed, ROM condition descriptions (quantified in degrees where available), muscle group assessed, measurement modality, training duration, and outcome values. Given the heterogeneity in outcome measurement methods across studies, a narrative synthesis approach was adopted as the primary mode of evidence synthesis, supplemented by effect size calculations where comparable outcomes were available.</p>
<h3>Muscle Length Determination</h3>
<p>For each study, the muscle length in each partial ROM condition was assessed based on the reported joint angle range and the anatomical relationship between joint position and muscle length. Studies were classified as examining "lengthened partials" if the ROM was restricted to the portion of movement associated with the greatest muscle elongation, and "shortened partials" if restricted to the region of least muscle elongation, based on established musculoskeletal geometry [4].</p>
<h2>Results</h2>
<h3>Study Selection</h3>
<p>The systematic search identified 1,284 records. After deduplication and screening, 12 studies were identified that met inclusion criteria. These studies investigated muscles including the elbow flexors (n = 5), plantar flexors (n = 3), knee extensors (n = 3), and hamstrings (n = 1). Training durations ranged from 4 to 16 weeks, and sample sizes ranged from 16 to 40 participants per study [1].</p>
<h3>Lengthened vs. Shortened Partial Repetitions</h3>
<p>Every study directly comparing lengthened versus shortened partial <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="ROM">ROM</a> training reported superior <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> in the lengthened-position training group. Across five such studies examining the elbow flexors and knee extensors, the advantage for <a href="/terms/lengthened-partial-repetitions/" class="term-link" data-slug="lengthened-partial-repetitions" title="lengthened partials">lengthened partials</a> was moderate to large, with Hedges' g values ranging from 0.48 to 0.91. Notably, in three of these studies, the advantage was statistically significant despite relatively small sample sizes, indicating robust effect magnitudes [2].</p>
<p>For the elbow flexors specifically (examined using preacher curl, incline dumbbell curl, or isokinetic conditions), lengthened partial training at or near full elbow extension produced 1.5- to 2.5-fold greater muscle thickness gains compared with shortened partial training at or near full elbow flexion. Similar patterns were observed for the vastus lateralis during knee extension partial ROM conditions.</p>
<h3>Lengthened Partials vs. Full ROM Training</h3>
<p>Three studies compared lengthened partial repetitions directly with full ROM training. Results were notably heterogeneous. Two studies found no significant difference between lengthened partials and full ROM training, with point estimates slightly favoring lengthened partials (g = 0.12 and g = 0.18 respectively, both non-significant). One study reported significantly greater hypertrophy in the lengthened partials condition (g = 0.44, p = 0.03). No study reported significantly greater hypertrophy in the full ROM condition compared with lengthened partials [3].</p>
<h3>Fascicle Length Outcomes</h3>
<p>In four studies reporting fascicle length, the pattern was consistent with the broader <a href="/terms/stretch-mediated-hypertrophy/" class="term-link" data-slug="stretch-mediated-hypertrophy" title="stretch-mediated hypertrophy">stretch-mediated hypertrophy</a> literature: lengthened partial training produced greater fascicle length increases than either shortened partial or full ROM training in two of four studies, with equivalent effects in the remaining two.</p>
<h2>Discussion</h2>
<h3>Position Matters More Than <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="ROM">ROM</a> Completeness</h3>
<p>The consistent finding across included studies that <a href="/terms/lengthened-partial-repetitions/" class="term-link" data-slug="lengthened-partial-repetitions" title="lengthened partial repetitions">lengthened partial repetitions</a> produce superior <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> compared with shortened partial repetitions, and potentially comparable hypertrophy to full ROM training, represents a paradigm-shifting implication for exercise science. The traditional directive to always train through a full range of motion—while useful as a general heuristic—obscures the more nuanced reality that the position within the ROM is the critical determinant of hypertrophic stimulus quality, not the completeness of joint excursion per se [1].</p>
<p>This conclusion aligns mechanistically with the broader <a href="/terms/stretch-mediated-hypertrophy/" class="term-link" data-slug="stretch-mediated-hypertrophy" title="stretch-mediated hypertrophy">stretch-mediated hypertrophy</a> literature [2]. The passive and active tension experienced by a muscle at long lengths—arising from titin-mediated passive stiffness, extracellular matrix contributions, and greater cross-bridge engagement at optimal <a href="/terms/sarcomere/" class="term-link" data-slug="sarcomere" title="sarcomere">sarcomere</a> operating lengths—appears to constitute a uniquely potent hypertrophic signal. By contrast, the shortened portion of the ROM, where these elongation-related forces are minimal, provides a comparatively attenuated stimulus for the same volume of work performed.</p>
<h3>Implications for Exercise Programming</h3>
<p>These findings support several practical programming strategies. First, when time constraints limit the total number of sets that can be performed, prioritizing lengthened-position partial repetitions over full ROM training may be an efficient strategy—achieving comparable hypertrophy with potentially less fatigue from the shortened portion of the movement, which also carries greater injury risk at high loads for some exercises [3].</p>
<p>Second, lengthened partial repetitions can be strategically added to existing full ROM training as supplementary work, particularly as "extended set" techniques following full ROM performance to failure. Performing additional partial repetitions in the stretched position after reaching failure on full ROM reps—a technique sometimes called "lengthened partials" or "bottom-end partials"—may provide additional mechanical stimulus at long muscle lengths after the shortened-position capacity is exhausted.</p>
<p>Third, exercise selection criteria should be reconsidered in light of these findings. Exercises providing high resistance at long muscle lengths (preacher curls, incline dumbbell curls, overhead cable triceps extensions, Romanian deadlifts, hack squats) may be preferentially effective for hypertrophy compared with exercises providing peak resistance in the shortened position (concentration curls at the top, prone leg curls in the shortened position) [4].</p>
<h3>Limitations and Future Research</h3>
<p>The current literature base is limited in several respects. Sample sizes in individual studies are small, training durations are typically short (4–12 weeks), and the muscle groups examined are limited. Long-term studies (24 weeks) examining whether the lengthened-partial advantage persists, and studies in trained populations where performance plateaus are common, are needed. Mechanistic studies examining molecular signaling differences between lengthened and shortened partial ROM training conditions in humans would substantially advance the theoretical understanding of these phenomena.</p>