Strength
Meta-Analysis
2017
The Effect of Training Strategies to Improve Muscle Strength and Endurance: A Meta-Analysis of Periodized vs. Non-Periodized Programs
By Tyler D. Williams, David V. Tolusso, Michael V. Fedewa and Michael R. Esco
Sports Medicine, 47(10), pp. 2083-2100
<h2>Abstract</h2>
<p><a href="/terms/periodization/" class="term-link" data-slug="periodization" title="Periodization">Periodization</a>—the systematic manipulation of training variables (volume, intensity, frequency, exercise selection, and rest) across structured time periods to optimize adaptation and performance—is considered a foundational principle of elite athletic preparation and has gained increasing attention in the broader resistance training literature. Despite widespread endorsement of periodized training approaches in professional guidelines, the quantitative evidence base comparing periodized with non-periodized resistance training programs for strength and endurance outcomes has been inconsistent in both scope and conclusions. The present <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> synthesized data from available controlled studies to estimate the effect of periodization on muscular strength and endurance adaptations relative to non-periodized training, and to compare the relative efficacy of distinct periodization models.</p>
<p>A systematic search identified 33 eligible controlled studies enrolling 1,102 participants. Random-effects meta-analyses were conducted for maximal strength (<a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>), muscle endurance, and composite performance outcomes. Subgroup analyses compared linear periodization (LP), daily undulating periodization (DUP), and weekly undulating periodization (WUP) against non-periodized (constant load) training conditions.</p>
<p>Periodized training programs produced significantly greater improvements in maximal strength compared with non-periodized programs, with a moderate pooled <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a>. Daily undulating periodization demonstrated a marginal but consistent advantage over linear periodization when directly compared. The benefit of periodization was more pronounced in individuals with greater training experience, suggesting that planned variation is particularly important as adaptations to any single training stimulus plateau. These findings support the systematic implementation of periodization principles in resistance training program design, particularly for intermediate and advanced trainees [1].</p>
<h2>Introduction</h2>
<p><a href="/terms/periodization/" class="term-link" data-slug="periodization" title="Periodization">Periodization</a> theory has its intellectual origins in the work of Hans Selye, whose General Adaptation Syndrome (GAS) model described the organism's adaptive response to stressors as progressing through stages of alarm, resistance, and exhaustion [1]. Applied to athletic training, this model implied that training stimuli must be progressively varied to prevent accommodation (where repeated exposure to an identical stimulus yields diminishing adaptive returns) and <a href="/terms/overtraining/" class="term-link" data-slug="overtraining" title="overtraining">overtraining</a> (where accumulated stress exceeds the organism's recovery capacity). Soviet sport scientists in the mid-20th century, notably Lev Matveyev, formalized these concepts into structured training planning models—what became known as classical or linear periodization—in which <a href="/terms/training-volume/" class="term-link" data-slug="training-volume" title="training volume">training volume</a> decreases and intensity increases systematically over months or years of preparation.</p>
<p>The classical linear periodization model dominated elite sports preparation for decades and was later adapted for recreational resistance training by exercise scientists including Tudor Bompa. In this model, training proceeds through distinct mesocycles (typically 3–6 weeks each) with progressively increasing intensity and decreasing volume: an initial <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> phase with high volume and moderate intensity transitions to a strength phase with moderate volume and high intensity, then to a power or peaking phase with low volume and very high intensity [2].</p>
<p>Critiques of classical linear periodization in the 1990s and 2000s pointed out that maintaining the same training emphasis for 3–6 weeks potentially led to <a href="/terms/detraining/" class="term-link" data-slug="detraining" title="detraining">detraining</a> in qualities not being emphasized (e.g., strength during hypertrophy blocks). This concern motivated the development of non-linear or undulating periodization models, in which training variables are varied more frequently—on a weekly (weekly undulating periodization, WUP) or daily (daily undulating periodization, DUP) basis. DUP, for example, might involve performing heavy strength-focused training on Monday (5 sets × 5 reps at 85% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>), moderate hypertrophy-focused training on Wednesday (4 sets × 10 reps at 70% 1RM), and lighter endurance-focused training on Friday (3 sets × 15 reps at 60% 1RM) within the same weekly cycle [3].</p>
<p>The proliferation of periodization models, each with theoretical justifications and practical advocates, has created uncertainty among practitioners and coaches about which approach is most effective. The present <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> was designed to systematically address this question by pooling the available evidence comparing periodized and non-periodized approaches, and by examining differences among periodization models, to provide evidence-based guidance for resistance training program design.</p>
<h2>Methods</h2>
<h3>Search Strategy</h3>
<p>A comprehensive search was performed in PubMed/MEDLINE, EMBASE, SPORTDiscus, CINAHL, and PsycINFO databases from their inception through the search date. Key search terms included "<a href="/terms/periodization/" class="term-link" data-slug="periodization" title="periodization">periodization</a>," "periodized training," "undulating periodization," "linear periodization," "daily undulating periodization," "non-linear periodization," "resistance training," "strength training," "muscular strength," "1 <a href="/terms/repetition-maximum/" class="term-link" data-slug="repetition-maximum" title="repetition maximum">repetition maximum</a>," and "muscular endurance" in various Boolean combinations. No language restrictions were applied. Reference lists of included studies and relevant reviews were hand-searched, and forward citation tracking was performed for landmark periodization studies.</p>
<h3>Eligibility Criteria</h3>
<p>Studies were included <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> they: (a) were peer-reviewed controlled experimental studies (RCTs or controlled trials) with human participants; (b) compared a periodized resistance training group with either (i) a non-periodized (constant load) resistance training control group or (ii) another periodized model (e.g., DUP vs. LP); (c) assessed maximal strength (<a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> or isokinetic peak torque) and/or muscular endurance at pre- and post-intervention time points; (d) had a training duration of at least eight weeks; and (e) provided sufficient data for <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> computation. Studies comparing periodized resistance training with no exercise, aerobic exercise, or other non-resistance exercise were excluded. Studies involving clinical populations with conditions directly affecting neuromuscular function (e.g., stroke, MS) were excluded.</p>
<h3>Classification of Periodization Models</h3>
<p>Periodization models were classified as: (1) Linear periodization (LP): systematic increase in intensity with concomitant decrease in volume across consecutive mesocycles of ≥3 weeks each; (2) Weekly undulating periodization (WUP): variation in training loads and volume on a weekly basis; (3) Daily undulating periodization (DUP): variation in training loads and volume across different sessions within the same week; and (4) Non-periodized (NP): constant load and volume maintained throughout the training period with only <a href="/terms/progressive-overload/" class="term-link" data-slug="progressive-overload" title="progressive overload">progressive overload</a> adjustments.</p>
<h3>Statistical Analysis</h3>
<p>Effect sizes (Hedges' g) were computed for each relevant comparison. <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="Positive">Positive</a> values indicated superiority of periodized (or DUP over LP) conditions. Random-effects models were applied throughout. Subgroup analyses compared LP, WUP, and DUP separately against NP conditions. Direct comparisons between periodization models were analyzed separately. Meta-regression examined training experience and program duration as moderators [4].</p>
<h2>Results</h2>
<h3>Study Inclusion and Sample Characteristics</h3>
<p>The database search identified 5,891 records. After deduplication and screening, 33 studies met all inclusion criteria. These studies enrolled 1,102 participants (mean age 24.7 years; 68% male). Training experience ranged from untrained to competitive athletes, and program durations ranged from 8 to 24 weeks. The breakdown of <a href="/terms/periodization/" class="term-link" data-slug="periodization" title="periodization">periodization</a> models compared was: LP vs. NP (n = 14 studies), DUP vs. NP (n = 11), WUP vs. NP (n = 5), and direct model-vs.-model comparisons (n = 12, including multiple studies with more than two conditions) [1].</p>
<h3>Periodized vs. Non-Periodized Training (Overall Effect)</h3>
<p>Pooling all periodized versus non-periodized comparisons, periodized training produced significantly greater maximal strength improvements than non-periodized training (Hedges' g = 0.43, 95% CI: 0.28–0.58, p 0.001; I² = 36%). This moderate and statistically robust effect indicates that systematic variation in training variables provides meaningful benefits over maintaining a constant training stimulus, even when total volume is equated.</p>
<h3>Periodization Model Subgroups</h3>
<p><strong>Linear periodization vs. NP</strong>: LP produced greater strength gains than NP (g = 0.37, 95% CI: 0.18–0.56, p 0.001), confirming the utility of systematic intensity-progression frameworks even in their most basic form.</p>
<p><strong>Daily undulating periodization vs. NP</strong>: DUP showed the largest advantage over NP in the strength comparison (g = 0.54, 95% CI: 0.31–0.77, p 0.001), with relatively low heterogeneity (I² = 21%) [2].</p>
<p><strong>DUP vs. LP direct comparisons</strong>: Among 12 studies directly comparing DUP and LP, DUP demonstrated a consistent but modest advantage for maximal strength development (g = 0.24, 95% CI: 0.08–0.40, p = 0.004). This finding suggests that more frequent variation in training stimuli produces superior adaptation compared with longer-duration, single-focus mesocycles.</p>
<h3>Effect of Training Experience</h3>
<p>Meta-regression identified training experience as a significant moderator (β = 0.18 per year of training experience, p = 0.01). Trained individuals showed larger periodization advantages (g = 0.55) compared with untrained individuals (g = 0.27), consistent with the hypothesis that accommodation to a fixed training stimulus develops more rapidly and more completely in more experienced trainees, making variety progressively more important [3].</p>
<h3>Muscular Endurance Outcomes</h3>
<p>For muscular endurance outcomes (available in 12 studies), periodized training showed a smaller but still statistically significant advantage over NP (g = 0.29, 95% CI: 0.11–0.47, p = 0.002).</p>
<h2>Discussion</h2>
<h3><a href="/terms/periodization/" class="term-link" data-slug="periodization" title="Periodization">Periodization</a> as a Superior Training Strategy</h3>
<p>The meta-analytic evidence presented here confirms that periodized resistance training programs produce meaningfully greater strength adaptations compared with non-periodized, constant-load training. The moderate pooled effect (g = 0.43) is practically significant and translates to meaningful real-world performance differences over training periods of 8–24 weeks. The consistency of this advantage across multiple periodization models (LP, WUP, DUP) and across studies of varying quality provides a robust empirical foundation for recommending periodized training as the standard approach for resistance training program design [1].</p>
<p>The biological rationale for the periodization advantage is grounded in accommodation theory. The neuromuscular and musculoskeletal systems adapt most rapidly to novel stimuli, with the rate of adaptation declining as any given stimulus becomes familiar. Repeated exposure to identical training loads, volumes, and exercise selections produces progressively smaller incremental gains—a phenomenon known as the repeated bout effect at the acute level and as accommodation or diminishing returns at the chronic level [2]. Periodization counters this by systematically introducing novel stimuli (through changes in load, volume, rep ranges, or exercise selection) before the adaptation to the current stimulus is fully exhausted, maintaining a chronically elevated adaptive response.</p>
<h3>Daily Undulating Periodization: Mechanistic Advantage</h3>
<p>The consistent advantage of DUP over both NP training and, to a lesser degree, LP may reflect the particularly effective manner in which DUP maintains concurrent development of multiple neuromuscular qualities. By varying training from heavy (strength-focused) to moderate (<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>-focused) to lighter (endurance-focused) within the same week, DUP potentially prevents the relative <a href="/terms/detraining/" class="term-link" data-slug="detraining" title="detraining">detraining</a> of strength qualities during hypertrophy-focused weeks (a potential limitation of LP) and vice versa [3]. This more frequent variation may better match the biological rhythms of <a href="/terms/supercompensation/" class="term-link" data-slug="supercompensation" title="supercompensation">supercompensation</a>, which operate on shorter timescales than traditional LP mesocycles allow.</p>
<h3>Training Experience as a Moderator</h3>
<p>The significantly larger periodization advantage in trained compared with untrained individuals has important prescription implications. Novice and early-intermediate trainees may achieve excellent results with relatively simple <a href="/terms/progressive-overload/" class="term-link" data-slug="progressive-overload" title="progressive overload">progressive overload</a> approaches without sophisticated periodization, as the "newbie gains" period features broad, non-specific adaptation to any form of progressive resistance training. As training experience accumulates and the organism becomes specifically adapted to the training stimuli employed, the introduction of systematic variation—in the form of structured periodization—becomes increasingly important to prevent stagnation and maintain progressive adaptation [4].</p>
<h3>Practical Periodization Implementation</h3>
<p>For practitioners implementing periodization in resistance training programs, the evidence supports the following practical approach: novice trainees (0–1 year experience) can begin with simple linear progression (adding small amounts of load or reps each session) without complex mesocycle planning. Intermediate trainees (1–3 years) benefit from introducing weekly undulating variation through different training focuses across sessions or sequential mesocycles of 4–6 weeks. Advanced trainees (3 years) are most likely to benefit from true DUP structures with daily variation in training focus within each week, combined with longer-term planned variation in emphasis across 12–16 week macrocycles.</p>
<p>In all cases, the foundational periodization principles—progressive overload, planned variation, and systematic incorporation of adequate recovery periods (<a href="/terms/deload/" class="term-link" data-slug="deload" title="deload">deload</a> weeks or reduced-volume phases every 4–8 weeks)—should be maintained regardless of the specific model employed. The goal is to balance accumulating fatigue with adaptation, preventing both chronic underload (insufficient stimulus) and <a href="/terms/overtraining/" class="term-link" data-slug="overtraining" title="overreaching">overreaching</a> (excessive cumulative fatigue) [1,3].</p>