Hypertrophy
Systematic Review
2021
Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum
By Brad J. Schoenfeld, Jozo Grgic, Derrick W. Van Every and Daniel L. Plotkin
Sports, 9(2), pp. 32
Abstract
<h2>Abstract</h2> <p>The traditional repetition continuum model of resistance training posits that distinct repetition ranges correspond to distinct physiological adaptations: low repetitions (1–5) with heavy loads favor maximal strength and neural adaptations, moderate repetitions (8–12) with moderate loads favor <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>, and high repetitions (15+) with light loads favor muscular endurance. While this heuristic model has been widely adopted in both academic and practitioner contexts, accumulating experimental evidence has substantially challenged its validity—particularly with respect to the hypertrophy component. The present paper re-examines the evidence underpinning the repetition continuum model and proposes a revised, evidence-based framework for loading recommendations.</p> <p>A review of available literature comparing hypertrophic outcomes across low, moderate, and high repetition ranges reveals that muscle hypertrophy is achievable across a broad spectrum of repetition ranges—from as few as 6 to as many as 35 repetitions per set—provided that sets are performed with sufficient effort (proximity to <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a>). The critical driver of hypertrophy appears to be the achievement of a high degree of <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment and <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic fatigue">metabolic fatigue</a> within the working set, which can be accomplished across a wide load range when effort is appropriately regulated.</p> <p>In contrast, the superiority of high-load training for maximal strength development appears more consistent in the literature, likely reflecting the importance of training specificity and neural adaptations at loads approaching <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>. These findings motivate revised loading recommendations that prioritize effort over specific load ranges for hypertrophy goals, while maintaining higher-load training recommendations for maximal strength objectives. Individual preferences, joint health, and exercise-specific load-<a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="ROM">ROM</a> characteristics should additionally guide loading selection in practice [1].</p>Introduction
<h2>Introduction</h2> <p>The concept of a repetition continuum—also termed the "rep range" or "loading zone" continuum—is among the most widely disseminated models in both academic exercise science curricula and practitioner-facing fitness education. In its conventional formulation, the model describes a spectrum from very heavy loads performed for few repetitions (1–5 reps at ≥85–90% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>) at one extreme, through moderate loads for moderate repetitions (8–12 reps at approximately 67–80% 1RM) in the middle, to light loads with high repetitions (≥15 reps at ≤67% 1RM) at the other extreme. Each zone is associated with a dominant physiological adaptation: maximal neuromuscular strength, <a href="/terms/myofibrillar-<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>/" class="term-link" data-slug="myofibrillar-hypertrophy" title="myofibrillar hypertrophy">myofibrillar hypertrophy</a>, and muscular endurance, respectively [1].</p> <p>The practical appeal of this model is considerable. It provides practitioners with a simple, memorable framework for exercise prescription aligned with training objectives, and it is broadly consistent with classical exercise physiology principles regarding the load-adaptation relationship. However, as evidence from controlled resistance training experiments has accumulated—particularly in the decade spanning roughly 2012–2022—the empirical foundations of the middle component of this continuum (the purported hypertrophy-specific zone of 8–12 reps) have been progressively undermined.</p> <p>A series of investigations by Schoenfeld, Mitchell, Morton, and colleagues demonstrated that training with loads as light as 30–35% 1RM (typically permitting 25–35+ repetitions before failure) produced hypertrophic gains statistically equivalent to those achieved with conventional moderate loads (8–12 reps), provided that sets were carried to volitional failure [2]. Similarly, high-load training (3–5 reps at 80–90% 1RM) produced comparable hypertrophy to moderate-load training in multiple studies, despite the markedly different loading context. These findings collectively suggest that the moderate-rep "hypertrophy zone" is neither uniquely nor optimally hypertrophic—any rep range with sufficient <a href="/terms/proximity-to-failure/" class="term-link" data-slug="proximity-to-failure" title="proximity to failure">proximity to failure</a> appears capable of eliciting comparable hypertrophic adaptations.</p> <p>At the same time, the evidence for the superiority of high-load training for maximal strength development has remained more robust, consistent with the principle of training specificity: neuromuscular adaptations supporting 1RM performance (improved intermuscular and intramuscular coordination, enhanced rate coding, reduced co-contraction) are most efficiently developed through training conditions that replicate 1RM testing demands [3]. This differential response in strength versus hypertrophy outcomes across the rep continuum motivates a re-examination and updating of the traditional model.</p>The Repetition Continuum Revisited
<h2>The Repetition Continuum Revisited</h2> <h3><a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="Hypertrophy">Hypertrophy</a> Across the Load Spectrum</h3> <p>The claim that hypertrophy is optimally produced within a specific moderate rep range is not supported by the accumulated evidence from controlled training studies. Multiple randomized controlled trials have directly compared hypertrophic outcomes across disparate loading conditions under volume-equated and effort-equated conditions.</p> <p>Mitchell et al. (2012) compared 3 sets of 30-repetition training at 30% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> with 3 sets of 10 repetitions at 80% 1RM in young men performing unilateral leg extension <a href="/terms/training-to-failure/" class="term-link" data-slug="training-to-failure" title="training to failure">training to failure</a>. Both conditions produced equivalent gains in type I and <a href="/terms/type-ii-muscle-fiber/" class="term-link" data-slug="type-ii-muscle-fiber" title="type II fiber">type II fiber</a> <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a> after 10 weeks, challenging the notion that low-load training was insufficient for hypertrophy [1]. Schoenfeld et al. (2017) similarly found comparable muscle thickness gains between groups training at 25–35 reps to failure versus 8–12 reps to failure with equated volume-loads. The consistency of these null differences across multiple studies and muscles has generated sufficient evidence to conclude that rep range per se—absent differences in effort—does not meaningfully differentiate hypertrophic outcomes.</p> <h3>The Critical Role of Effort</h3> <p>The mechanism underlying the apparent rep-range independence of hypertrophy likely involves the concept of <a href="/terms/proximity-to-failure/" class="term-link" data-slug="proximity-to-failure" title="proximity to failure">proximity to failure</a> and the <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment dynamics that accompany it. As a set approaches <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a>—regardless of the load used—the nervous system is compelled to progressively increase motor unit recruitment and firing rates to maintain force output against the declining capacity of fatigued fibers. By the final repetitions of any set taken to or near failure, high-threshold (fast-twitch, Type II) motor units are maximally recruited [2].</p> <p>This "failure-mediated recruitment" mechanism means that even very light loads, when taken to the point where no further repetitions can be completed, engage the entire spectrum of motor units—including those of highest hypertrophic potential. By contrast, sets terminated far from failure at any load will leave high-threshold motor units under-recruited and provide a submaximal stimulus. This framework implies that effort (measured as proximity to failure in repetitions-in-reserve, or <a href="/terms/repetitions-in-reserve/" class="term-link" data-slug="repetitions-in-reserve" title="RIR">RIR</a>) is a more important determinant of hypertrophic stimulus quality than the absolute load or rep count per se.</p> <h3>Differential Strength Response</h3> <p>While hypertrophy appears relatively load-agnostic when effort is matched, the same cannot be said for maximal strength. High-load training (≥80% 1RM) consistently produces superior improvements in 1RM performance compared with low-load training in meta-analytic data. This discrepancy is attributable to training specificity: the neural adaptations that support 1RM performance—including enhanced inter-muscular coordination, improved motor pattern efficiency, and psychological familiarity with handling near-maximal loads—are specifically developed through practice at near-maximal intensities [3]. Moderate and low-load training, even when producing equivalent hypertrophy, does not fully develop these neural adaptations.</p> <h3>Practical Implications of the Revised Model</h3> <p>The revised repetition continuum model therefore distinguishes between hypertrophy and maximal strength as distinct goals requiring partially different loading strategies. For pure hypertrophy goals, any rep range (roughly 6–35+ reps) taken close to failure is viable, enabling practitioners to select rep ranges based on practical considerations including joint comfort, exercise type, individual preference, and time efficiency [1,3].</p>Practical Recommendations
<h2>Practical Recommendations</h2> <h3>Loading for Maximal Strength</h3> <p>For individuals whose primary goal is the development of maximal muscular strength—as measured by performance on <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> tests or competitive powerlifting/weightlifting tasks—the evidence supports a predominance of high-load training within the 1–6 repetition range at intensities of 80–100% 1RM. This recommendation aligns with the principle of training specificity and is supported by multiple meta-analyses demonstrating superior 1RM performance outcomes with high-load protocols [1]. Volume for strength development should include regular practice of competition-specific or assessment-specific movements at near-maximal intensities, supplemented by submaximal volumes in the moderate-rep range for hypertrophic mass development that supports the structural basis for strength expression.</p> <h3>Loading for <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="Muscle Hypertrophy">Muscle Hypertrophy</a></h3> <p>For individuals whose primary goal is maximizing skeletal muscle <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a> and volume, the evidence supports a flexible approach across the 6–35 repetition range, provided that sets are performed within 0–4 repetitions of volitional <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a> (0–4 <a href="/terms/repetitions-in-reserve/" class="term-link" data-slug="repetitions-in-reserve" title="RIR">RIR</a>). Rather than rigidly adhering to a specific "hypertrophy zone," practitioners may select rep ranges based on the following considerations:</p> <p><strong>Moderate rep ranges (8–15 reps)</strong> represent a practical "sweet spot" for most exercises and muscle groups: the loads used are heavy enough to provide meaningful <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a>, while the higher rep count relative to pure strength training generates significant <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic stress">metabolic stress</a>. The familiar moderate-rep range remains a valid and effective choice, even <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> it is no longer uniquely optimal.</p> <p><strong>Lower rep ranges (6–8 reps)</strong> are appropriate for compound movements (squats, deadlifts, rows, bench press) where biomechanical demands may limit the ability to perform high-rep sets safely, or where the practitioner wishes to simultaneously develop strength and hypertrophy. High-load training produces equivalent hypertrophy with potentially greater strength carryover [2].</p> <p><strong>Higher rep ranges (15–30+ reps)</strong> are advantageous when joint discomfort, injury rehabilitation requirements, or exercise characteristics (e.g., cable exercises, bodyweight exercises) favor lower absolute loads. They are also effective for certain isolation exercises where the lighter weight used reduces injury risk while still driving meaningful hypertrophy when taken to failure.</p> <h3>Rep Range Variation</h3> <p>Incorporating varied rep ranges across a training program—either within the same session or across different training blocks (<a href="/terms/periodization/" class="term-link" data-slug="periodization" title="periodization">periodization</a>)—offers practical advantages. Different rep ranges may emphasize different hypertrophic mechanisms (mechanical tension at lower reps, metabolic stress at higher reps) to a varying degree, and variety may enhance long-term adherence and prevent accommodation [3].</p>Conclusions
<h2>Conclusions</h2> <p>The traditional repetition continuum model, while historically useful as an introductory teaching framework, requires substantial revision in light of contemporary evidence. The most important revision concerns the <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> component: skeletal muscle hypertrophy is not uniquely or optimally produced within a narrow moderate rep range, but is achievable across a broad spectrum from approximately 6 to 35+ repetitions per set when effort is matched and sets are taken to or near volitional failure [1].</p> <p>This conclusion has meaningful implications for clinical exercise prescription, athletic training program design, and basic exercise science pedagogy. It liberates practitioners from unnecessary prescriptive rigidity and permits individualized loading strategies tailored to the specific constraints, preferences, and goals of each individual. An older adult with knee osteoarthritis may perform high-rep, low-load <a href="/terms/training-to-failure/" class="term-link" data-slug="training-to-failure" title="training to failure">training to failure</a> and achieve comparable hypertrophy to a younger athlete training with heavy loads. An advanced powerlifter may include high-rep accessory work in their program without sacrificing hypertrophic benefit. This flexibility represents a significant practical advance.</p> <p>The qualification that effort—specifically proximity to <a href="/terms/momentary-muscular-failure/" class="term-link" data-slug="momentary-muscular-failure" title="muscular failure">muscular failure</a>—is the critical governing variable for hypertrophy regardless of load is perhaps the most actionable single takeaway from this revised model. Practitioners should ensure that training sets are performed with sufficiently high effort to recruit high-threshold motor units and generate robust <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic stress">metabolic stress</a>, and should prioritize this over rigid adherence to specific load or rep count targets [2].</p> <p>For maximal strength development, high-load training (≥80% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>) retains its primacy. The neural adaptations supporting 1RM performance are load-specific and are most effectively developed through practice at near-maximal intensities. Strength-focused trainees therefore benefit from maintaining a foundation of high-load training even <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> they supplement with broader rep ranges for hypertrophic volume.</p> <p>Future research should continue to examine the long-term <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a> of different loading strategies, the specific mechanisms by which low-load training to failure produces hypertrophy equivalent to high-load training, and whether specific populations or individual characteristics predict differential responses to different loading approaches. The repetition continuum model, in its revised form, offers a more nuanced and empirically grounded foundation for evidence-based resistance training program design [3].</p>관련 논문
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