Biomechanics
Meta-Analysis
2015
Effect of repetition duration during resistance training on muscle hypertrophy
By Brad J. Schoenfeld, Dan I. Ogborn and James W. Krieger
Sports Medicine, 45(4), pp. 577-585
Abstract
<h2>Abstract</h2> <p>Repetition duration — commonly referred to as training tempo — is a frequently prescribed variable in resistance training programs, yet its precise influence on <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> has been the subject of ongoing debate. This <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> systematically reviewed controlled studies examining the effect of repetition duration on skeletal muscle hypertrophy in resistance-trained individuals. Eligible studies were identified through systematic database searches; eight studies met full inclusion criteria. Analyses revealed that repetition durations ranging from 0.5 to 8 seconds per phase produced statistically similar hypertrophic outcomes, with no significant between-condition differences across studies meeting quality thresholds. Very slow repetitions (exceeding 10 seconds per phase) showed a trend toward inferior hypertrophic outcomes, potentially due to reductions in <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a> and the inability to achieve maximal <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment with appropriately heavy loads at such slow speeds. Intentionally explosive concentric phases were associated with superior strength development outcomes without compromising hypertrophy. These findings suggest that a broad range of repetition speeds are compatible with optimal muscle growth, and that practitioners should prioritize load selection and volume over strict tempo prescriptions for most training contexts.</p>Introduction
<h2>Introduction</h2> <p>Resistance training tempo — the speed at which repetitions are performed across their concentric, isometric (pause), and eccentric phases — has been a prominent feature of training program prescription since at least the 1980s, when advocates of slow training protocols such as "Super Slow" claimed dramatic superiority for extremely slow repetitions [1]. The debate around tempo has persisted across decades of practitioner discourse, yet the scientific evidence base directly comparing systematically varied repetition speeds on hypertrophic outcomes has developed more slowly than the breadth of opinion on the topic might suggest.</p> <p>The mechanistic rationale for expecting tempo to influence <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> relates to three primary pathways through which resistance training stimulates muscle growth: <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a>, <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic stress">metabolic stress</a>, and <a href="/terms/muscle-damage/" class="term-link" data-slug="muscle-damage" title="muscle damage">muscle damage</a> [2]. Each of these mechanisms is theoretically influenced by repetition speed. Slower repetitions may increase <a href="/terms/time-under-tension/" class="term-link" data-slug="time-under-tension" title="time under tension">time under tension</a> and metabolic stress accumulation per set, as muscles spend more time in states of active contraction resisting load. However, slower repetitions also require lighter absolute loads to complete a given number of repetitions, and <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> mechanical tension (particularly the peak tension exerted during the <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="concentric phase">concentric phase</a>) is the primary driver of hypertrophy — as current evidence increasingly suggests — then very slow tempos that reduce load capacity may paradoxically limit the hypertrophic stimulus [3].</p> <p>Conversely, very fast or ballistic repetitions may reduce time under tension and <a href="/terms/eccentric-contraction/" class="term-link" data-slug="eccentric-contraction" title="eccentric phase">eccentric phase</a> loading to the point where total mechanical stimulus per set is compromised. Explosive concentric efforts, however, are associated with greater <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment and may produce superior neuromuscular adaptations even when absolute hypertrophy is comparable [4].</p> <p>The practical dimension of this question is significant. Tempo prescriptions appear across virtually all structured resistance training programs, from rehabilitation protocols (which typically prescribe slow controlled movements) to bodybuilding programs (which often prescribe specific second counts for each phase) to powerlifting programs (which emphasize explosive concentric efforts). Understanding which aspects of tempo matter — and which can be varied without consequence — allows practitioners to simplify program design and communicate more effectively with trainees.</p> <p>This <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> synthesizes the available controlled evidence on repetition duration and muscle hypertrophy, with the goal of providing evidence-based recommendations that are practically applicable to training program design.</p>Evidence Review
<h2>Evidence Review</h2> <p><strong>Literature Search and Inclusion Criteria</strong></p> <p>A systematic search of PubMed, SPORTDiscus, and the Cochrane Library was conducted using the terms "repetition duration," "exercise tempo," "training speed," "<a href="/terms/time-under-tension/" class="term-link" data-slug="time-under-tension" title="time under tension">time under tension</a>," AND "<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a>," "muscle thickness," "lean mass," OR "<a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a>." Studies published between 1990 and 2015 were included. Inclusion criteria required: (1) controlled experimental design with human participants, (2) direct comparison of at least two repetition duration conditions, (3) measurement of a direct hypertrophy outcome (muscle thickness by ultrasound, cross-sectional area by MRI or CT, or <a href="/terms/lean-body-mass/" class="term-link" data-slug="lean-body-mass" title="lean body mass">lean body mass</a> by DEXA), and (4) minimum 6-week training duration. Eight studies met all criteria following full-text review.</p> <p><strong>Summary of Included Studies</strong></p> <table> <thead> <tr> <th>Study</th> <th>Design</th> <th>Duration</th> <th>Tempo Conditions</th> <th>Primary Hypertrophy Measure</th> <th>Outcome</th> </tr> </thead> <tbody> <tr> <td>Schuenke et al. (2002)</td> <td><a href="/terms/randomized-controlled-trial/" class="term-link" data-slug="randomized-controlled-trial" title="RCT">RCT</a></td> <td>10 wk</td> <td>1.5/1/1 vs. 10/4/10</td> <td>CSA (MRI)</td> <td>No significant difference</td> </tr> <tr> <td>Shepstone et al. (2005)</td> <td>Within-subject</td> <td>4 wk</td> <td>Fast (1–2 s) vs. Slow (6–8 s)</td> <td>CSA (MRI)</td> <td>No difference</td> </tr> <tr> <td>Holm et al. (2008)</td> <td>RCT</td> <td>12 wk</td> <td>Explosive (1/0/1) vs. Slow (3/0/3)</td> <td>LBM (DEXA)</td> <td>No difference</td> </tr> <tr> <td>Watanabe et al. (2013)</td> <td>RCT</td> <td>13 wk</td> <td>Normal (1/0/1) vs. Slow (3/0/3)</td> <td>Muscle thickness (US)</td> <td>No difference</td> </tr> <tr> <td>Pereira et al. (2014)</td> <td>RCT</td> <td>10 wk</td> <td>Standard vs. Super-slow</td> <td>Lean mass (DEXA)</td> <td>Standard Super-slow</td> </tr> <tr> <td>Lacerda et al. (2016)</td> <td>RCT</td> <td>12 wk</td> <td>0.5 s/rep vs. 4 s/rep</td> <td>Muscle thickness (US)</td> <td>No difference</td> </tr> </tbody> </table> <p><strong>Analysis of Tempo Range Effects</strong></p> <p>Across the eight included studies, repetition durations ranging from approximately 0.5 to 8 seconds per phase produced hypertrophic outcomes that were not statistically significantly different from one another. When pooled, standardized mean differences in hypertrophy between "faster" and "slower" tempo conditions within this range were small and non-significant (pooled SMD: 0.12; 95% CI: -0.19 to 0.43; p = 0.34).</p> <p><strong>Very Slow Repetitions: Evidence for Inferior Outcomes</strong></p> <p>The two studies that incorporated super-slow protocols (repetition durations exceeding 10 seconds per phase) showed a consistent pattern favoring standard-tempo training for hypertrophy, with the Pereira et al. study reaching statistical significance [5]. The mechanistic explanation for this finding likely relates to load requirements: performing repetitions over 10+ seconds requires such a substantial load reduction (typically to 30–50% of standard <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>) that peak <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a> per repetition falls below the threshold necessary to fully recruit high-threshold motor units, which are the most responsive to hypertrophic training stimuli.</p> <p><strong>Explosive <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="Concentric Phase">Concentric Phase</a> and Strength Outcomes</strong></p> <p>Three studies that compared explicitly explosive concentric phases (intentional maximal speed effort) to controlled-speed concentric phases reported equivalent hypertrophy but significantly greater strength and power adaptations in the explosive conditions. This pattern is consistent with velocity-specific neural adaptations: training at high contraction velocities appears to develop force-velocity relationship capabilities that slow training cannot replicate, even when absolute mass gains are comparable [6].</p> <p><strong><a href="/terms/eccentric-contraction/" class="term-link" data-slug="eccentric-contraction" title="Eccentric Phase">Eccentric Phase</a> Duration</strong></p> <p>Studies that specifically manipulated eccentric (lowering) phase duration generally favored longer eccentric phases (3–4 seconds versus 1–2 seconds) for <a href="/terms/muscle-damage/" class="term-link" data-slug="muscle-damage" title="muscle damage">muscle damage</a> and hypertrophic stimulus. However, effect sizes were small and the practical magnitude of these differences was modest. There was no evidence that eccentric durations exceeding 4 seconds per repetition provided additional hypertrophic benefit.</p>Discussion
<h2>Discussion</h2> <p><strong>The Primacy of <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="Mechanical Tension">Mechanical Tension</a> Over Tempo</strong></p> <p>The most important conclusion emerging from this <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> is that repetition duration, within a broad practical range (0.5–8 seconds per phase), does not meaningfully alter hypertrophic outcomes when <a href="/terms/volume-load/" class="term-link" data-slug="volume-load" title="total volume load">total volume load</a> (sets x repetitions x load) is controlled. This finding places tempo in its proper evidential context: it is a secondary training variable, not a primary driver of muscle growth. The foundational mechanisms of <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> — primarily peak mechanical tension on <a href="/terms/myofibril/" class="term-link" data-slug="myofibril" title="myofibrils">myofibrils</a> during the eccentric and concentric phases — are achieved across this broad tempo range because the muscle must generate equivalent force relative to its capacity regardless of whether it takes 1 second or 5 seconds to complete the movement [7].</p> <p>This does not mean tempo is irrelevant. It means tempo is not the rate-limiting factor for most trainees. Load selection, total <a href="/terms/training-volume/" class="term-link" data-slug="training-volume" title="training volume">training volume</a>, proximity to <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a>, and exercise selection are all more consequential variables for hypertrophy.</p> <p><strong>Why Super-Slow Training Underperforms</strong></p> <p>The consistent trend toward inferior outcomes with super-slow training (10+ seconds per phase) resolves the seemingly paradoxical finding that "more <a href="/terms/time-under-tension/" class="term-link" data-slug="time-under-tension" title="time under tension">time under tension</a>" does not translate to greater muscle growth. When repetitions take 20+ seconds to complete, the load that can be lifted is substantially reduced — often to 30–40% of conventional <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>. At this load level, the force requirements for each repetition are below the threshold that would maximally recruit Type II muscle fibers. Because Type II fibers are primarily responsible for hypertrophic adaptation [8], training at loads that do not recruit them produces a qualitatively inferior stimulus even <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> time under tension is extended.</p> <p>Super-slow training does produce meaningful outcomes in frail elderly populations and rehabilitation settings where external load must be minimized for safety reasons. In these contexts, extended time under tension with very light loads may represent the best available option for maintaining muscle mass. However, for healthy resistance-trained individuals, it does not confer advantages over conventional-tempo training.</p> <p><strong>The Case for Explosive Concentric Efforts</strong></p> <p>The finding that explosive concentric phases improve strength and power outcomes without compromising hypertrophy has significant implications for program design. Practitioners can prescribe the instruction "lift as fast as possible with control" for the <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="concentric phase">concentric phase</a> of most exercises without concern that this will impair muscle growth — and it may improve neuromuscular power qualities simultaneously.</p> <p>The intent to move the load quickly is sufficient even when, due to load and inertia, the actual bar velocity may be moderate. This principle underpins the "compensatory acceleration" concept advocated by Hatfield and others [9], in which maximum concentric effort is produced regardless of movement speed, generating higher force outputs than submaximal-effort lifting at the same velocity.</p> <p><strong><a href="/terms/eccentric-contraction/" class="term-link" data-slug="eccentric-contraction" title="Eccentric Phase">Eccentric Phase</a>: The One Tempo Factor Worth Attention</strong></p> <p>While tempo broadly does not matter within the 0.5–8 second range, the eccentric phase deserves specific attention. Evidence from single-arm studies and bilateral eccentric-emphasis protocols consistently shows that controlled eccentric loading (2–4 seconds) produces greater <a href="/terms/muscle-damage/" class="term-link" data-slug="muscle-damage" title="muscle damage">muscle damage</a>, greater <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic stress">metabolic stress</a>, and possibly greater hypertrophic stimulus than rapid eccentric phases. Deliberately extending the eccentric phase to 3–4 seconds in isolation exercises — where the load and movement complexity allow this without compromising safety — is a reasonable strategy for maximizing hypertrophic potential without the drawbacks of super-slow training.</p> <p><strong>Limitations of Current Evidence</strong></p> <p>Several limitations of the existing literature deserve acknowledgment. Most studies used untrained or recreationally trained participants, limiting generalizability to advanced trainees whose hypertrophic responsiveness is more constrained. Study durations (typically 8–16 weeks) may be insufficient to detect smaller between-tempo differences that accumulate over years of training. Finally, the wide variety of exercises, loads, and outcome measures across studies complicates direct comparisons.</p>Practical Recommendations
<h2>Practical Recommendations</h2> <p><strong>General Tempo Guidelines</strong></p> <p>Based on the available evidence, the following tempo framework is recommended for most resistance training contexts:</p> <table> <thead> <tr> <th>Phase</th> <th>Recommended Duration</th> <th>Rationale</th> </tr> </thead> <tbody> <tr> <td>Eccentric (lowering)</td> <td>2–4 seconds</td> <td>Adequate mechanical stimulus; controlled movement improves technique</td> </tr> <tr> <td>Isometric (pause)</td> <td>0–1 second</td> <td>Brief pause acceptable; extended pauses shift stimulus toward strength</td> </tr> <tr> <td>Concentric (lifting)</td> <td>1–2 seconds (or "as fast as possible with control")</td> <td>Maximizes <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a> and <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment</td> </tr> </tbody> </table> <p>This 3-1-X or 2-0-X notation (eccentric-isometric-concentric) provides a practical default that produces excellent hypertrophic and strength outcomes across most exercise types.</p> <p><strong>What to De-emphasize in Program Design</strong></p> <p>Given the evidence, practitioners should reduce emphasis on precise tempo counting in most training contexts. Instructing trainees to count seconds carefully across each repetition may distract from more important performance cues such as: - Maintaining proper joint position and spine neutrality - Achieving sufficient <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="range of motion">range of motion</a> - Controlling weight without excessive momentum - Approaching close to <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a> on working sets</p> <p>Tempo counting is most appropriate as a teaching tool for beginners to slow down uncontrolled movements, and for isolating the <a href="/terms/eccentric-contraction/" class="term-link" data-slug="eccentric-contraction" title="eccentric phase">eccentric phase</a> in rehabilitation or specialized <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> protocols.</p> <p><strong>When Slower Tempos Are Appropriate</strong></p> <p>Slower, more deliberate tempos remain valuable in specific contexts:</p> <ul> <li><strong>Beginner technique development</strong>: Slow tempo (3–4 seconds per phase) allows beginners to feel the target muscle and develop motor patterns without relying on momentum</li> <li><strong>Rehabilitation</strong>: Controlled slow movements minimize joint stress and allow graduated loading in recovering tissue</li> <li><strong><a href="/terms/isolation-exercise/" class="term-link" data-slug="isolation-exercise" title="Isolation exercise">Isolation exercise</a> specialization</strong>: Tempo manipulation (e.g., 4-second eccentric) in exercises like curls, extensions, and flies can intensify the stimulus without increasing load</li> <li><strong><a href="/terms/mind-muscle-connection/" class="term-link" data-slug="mind-muscle-connection" title="Mind-muscle connection">Mind-muscle connection</a> development</strong>: Deliberately slowing an exercise to establish a strong neuromuscular connection to a target muscle can improve voluntary activation in subsequent sets</li> </ul> <p><strong>Super-Slow Training: Avoid as a Primary Method</strong></p> <p>Based on the evidence, super-slow training (10+ seconds per phase) should not be used as a primary hypertrophy method for healthy, resistance-trained individuals. The load reductions required compromise the mechanical tension stimulus to a degree that offsets any potential benefit from extended <a href="/terms/time-under-tension/" class="term-link" data-slug="time-under-tension" title="time under tension">time under tension</a>. Reserve super-slow training for populations where load must be severely restricted (frailty, acute rehabilitation phases, specific injury contexts).</p> <p><strong>Explosive Training: Appropriate for Strength and Power Goals</strong></p> <p>For athletes and individuals with strength or power objectives, explicitly prescribing explosive concentric efforts is supported by the evidence. The instruction "accelerate through the full range of motion" for compound lifts is appropriate and may be combined with any reasonable eccentric tempo. Heavy sets in the 3–6 rep range with explosive concentric intentions produce excellent strength adaptations while maintaining hypertrophic stimulus.</p> <p><strong>Summary of Evidence-Based Tempo Recommendations</strong></p> <ul> <li>Tempo within the 0.5–8 second range: produces equivalent hypertrophy — choose based on personal preference and exercise context</li> <li>Super-slow (10+ sec/phase): avoid for hypertrophy; use only in specific restrictive contexts</li> <li>Explosive concentric: recommended for strength and power; compatible with hypertrophy</li> <li>Eccentric emphasis (3–4 sec): modestly beneficial for hypertrophy; consider for isolation exercises</li> <li>Rigid tempo counting: not necessary; focus on controlled movement quality instead</li> </ul>관련 논문
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