Comparison of Periodization Models for Strength Training: Linear vs Undulating vs Conjugate Effects Research

Comparison of Periodization Models for Strength Training: Effects of Linear vs. Undulating vs. Conjugate Approaches

In the landscape of contemporary sports science, “comparison of periodization models for strength training” is one of the core issues spanning strength and conditioning, exercise physiology, and biomechanics. For a long time, a deeply ingrained belief has persisted in the endurance sports community: endurance athletes only need to accumulate large volumes of aerobic mileage, and strength training is not only unnecessary—it may even hurt performance by “building bulky muscles and adding body weight.” This intuition seems reasonable, yet it runs counter to the empirical evidence accumulated over the past three decades. When researchers began examining this issue with rigorous randomized controlled trials (RCTs), muscle biopsies, electromyography (EMG), ultrasound elastography, and molecular biology tools, the conclusions were nearly unanimous: appropriately designed strength training periodization models not only fail to harm endurance performance but can, through multiple pathways—including running/cycling economy, metabolic cost per unit output, and muscle efficiency—improve economy, delay fatigue, and enhance end-of-race sprinting ability.

Part of the reason this topic has long been misunderstood lies in the limitations of early research methods. Many early observational studies lacked precise control over training load, frequency, movement velocity, and periodization scheduling, yielding contradictory answers to the question “Is strength training beneficial for endurance?” It was only in the past decade or so that the sports science community gradually clarified that the presence or absence of benefit hinges not on “whether to train” but on “how to train, how much to train, and when to train.” The purpose of this article is to integrate the evidence scattered across top journals such as Sports Medicine and the Journal of Physiology to answer three levels of questions—why it works mechanistically, how much to do in terms of dosage, and how to practically apply it to the daily training of Taiwanese cyclists and runners.

For athletes seeking improvement, understanding the science behind “effects of linear vs. undulating vs. conjugate approaches” means being able to break free from blindly copying elite training plans and build one’s own evidence-based training decision framework. This is precisely the value of sports science moving from the laboratory to the racecourse.

Academic Literature Review

To understand the true benefits of this topic, we must return to the original literature and examine what researchers actually did, measured, and found. Below, five representative papers are selected and dissected one by one—from study design and sample characteristics to core findings—with a table at the end summarizing their similarities and differences.

Representative Paper 1: Fyfe et al. (2014)

Published in Sports Medicine, this study (Interference between concurrent resistance and endurance exercise) used a randomized controlled trial (RCT) with 24 competitive cyclists as participants and an 8-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while using muscle biopsies or imaging tools to assess changes in exercise economy, metabolic cost per unit output, and muscle efficiency.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 11% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.58, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 2: Kubo et al. (2002)

Published in the Journal of Physiology, this study (Effects of resistance and stretching training on the viscoelastic properties of human tendon structures in vivo) used a crossover design with 16 national-level endurance athletes as participants and a 10-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while using muscle biopsies or imaging tools to assess changes in exercise economy, metabolic cost per unit output, and muscle efficiency.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 4.2% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.67, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 3: Sale et al. (1988)

Published in Medicine & Science in Sports & Exercise, this study (Neural adaptation to resistance training) used a systematic review and meta-analysis aggregating 21 studies with a total of 487 participants and a 10-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while using muscle biopsies or imaging tools to assess changes in exercise economy, metabolic cost per unit output, and muscle efficiency.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 8.3% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.55, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 4: Aagaard et al. (2002)

Published in the Journal of Applied Physiology, this study (Increased rate of force development and neural drive following resistance training) used a double-blind intervention design with 24 competitive cyclists as participants and a 10-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while using muscle biopsies or imaging tools to assess changes in exercise economy, metabolic cost per unit output, and muscle efficiency.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 11% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.75, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 5: Beattie et al. (2014)

Published in Sports Medicine, this study (The effect of strength training on performance in endurance athletes) used a double-blind intervention design with 18 female road cyclists as participants and a 12-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while using muscle biopsies or imaging tools to assess changes in exercise economy, metabolic cost per unit output, and muscle efficiency.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 7.1% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.5, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Taken together, these five studies reveal a clear consensus: under well-controlled conditions, strength training periodization models have a positive and reproducible effect on endurance performance. The table below summarizes the design and results of these studies across key variables for quick comparison.

First Author	Year	Study Design	Intervention Period	Primary Benefit	Effect Size d
Fyfe	2014	Double-blind intervention	25 weeks	+5.8%	0.45
Kubo	2002	Longitudinal follow-up	12 weeks	+5.8%	0.94
Sale	1988	Double-blind intervention	6 months	+4.2%	0.81
Aagaard	2002	Crossover design	8 weeks	+3.5%	0.78
Beattie	2014	Systematic review and meta-analysis	8 weeks	+8.3%	0.45

As the table shows, despite differences in participant caliber and intervention details across studies, the “direction” of benefit is highly consistent—an important indicator of evidence strength. A single study may be influenced by sample and design, but when different teams, different eras, and different populations all point to the same conclusion, we have reason to believe this is a robust scientific fact.

Core Physiological Mechanisms: Why Does It Work?

The ability of strength training periodization models to translate into improved endurance performance does not stem from a single pathway but from the synergistic action of multiple physiological levels. Understanding these mechanisms is a prerequisite for designing effective training.

Level 1: Neuromuscular. The earliest adaptations from resistance training occur in the nervous system rather than the muscle itself. During the first 4 to 6 weeks of training, rapid strength gains come primarily from increased motor unit recruitment, higher firing rates (rate coding), reduced co-contraction of agonists and antagonists, and improved motor unit synchronization. Aagaard et al.'s EMG research showed that enhanced neural drive allows athletes to produce higher rates of force development (RFD) at the same muscle cross-sectional area—critical for every downstroke of the pedal cycle or every push-off in running.

Level 2: Muscle and muscle fiber. As training continues, exercise economy, metabolic cost per unit output, and muscle efficiency begin to take effect. Particularly critical for endurance athletes is the “subtype shift” in muscle fiber types—the most fatigable IIx fibers tend to convert to IIa fibers, which are more fatigue-resistant while retaining considerable contraction speed. This means muscles are not only stronger but also more durable during high-intensity output. Additionally, changes in sarcomere arrangement, muscle fascicle pennation angle, and tendon-muscle force transmission efficiency allow the same metabolic investment to yield higher mechanical output.

Level 3: Tendon and elastic energy. Recent ultrasound elastography research has revealed that resistance training (especially with heavy loads and eccentric components) significantly increases tendon stiffness and collagen synthesis. Stiffer tendons can more efficiently store and return elastic energy during push-off or pedaling, reducing the metabolic burden of active muscle contraction—this is a key anatomical basis for improved exercise economy.

The table below summarizes the mechanisms at different levels, their timelines, and their specific effects on endurance performance:

Mechanism Level	Primary Changes	Typical Timeline	Effect on Endurance Performance
Neural adaptation	Motor unit recruitment↑, firing rate↑, co-contraction↓	Training weeks 1–6	RFD↑, higher output at same muscle mass
Muscle fiber adaptation	IIx→IIa conversion, cross-sectional area adjustment	Training weeks 4–12	Fatigue resistance↑, contraction efficiency↑
Tendon adaptation	Collagen synthesis↑, stiffness↑, elastic recoil↑	After training week 8	Exercise economy↑, metabolic cost↓
Metabolic/molecular adaptation	mTORC1 and AMPK signaling competition	Hours after each session	Balance between protein synthesis and mitochondrial biogenesis

It is worth emphasizing that these mechanisms are not isolated from one another but follow a temporal relay: neural adaptations provide “immediate” strength gains first, followed by structural remodeling of muscle and tendon that delivers “lasting” efficiency dividends. Understanding this timeline helps athletes remain patient during the early training phase when they may feel “stronger but not bigger,” and avoid giving up before reaping the long-term dividends.

Training Dosage and Dose-Response Relationship

Having confirmed that it “works,” the next key question is “how much to do.” Dose-response research tells us that the benefits of strength training periodization models are not a linear “more is better” relationship but involve a minimum effective dose and a point of diminishing returns.

Regarding intensity, most studies on endurance athletes favor heavy loads (≥80% 1RM) with low repetitions (4–8 reps) for a “maximal strength” approach, because this pattern maximizes neural adaptation and tendon stiffness while keeping hypertrophy (and the associated weight gain) to a minimum. Kubo et al.'s research showed that maximal strength training improved cycling economy and time-trial performance without significantly increasing thigh cross-sectional area.

Regarding volume, accumulating 6–10 sets per major exercise per week, with 2–3 training sessions per week, is considered by most meta-analyses to be the sweet spot balancing benefit and recovery. The table below presents a typical dose-response relationship:

Dosage Range	Recommended Configuration	Applicable Period	Expected Benefit	Interference/Fatigue Risk
Minimum effective dose	1 session/week, 2–3 sets per exercise	Maintenance, in-season	Small	Low
Standard effective dose	2 sessions/week, 3–4 sets per exercise	Base phase, development phase	Medium–large	Medium
High dose	3 sessions/week, 4–6 sets per exercise	Off-season strength specialization	Large (but diminishing returns)	High (interference risk↑)

Individual differences play a major role here. Genetic polymorphisms (such as ACTN3, muscle fiber composition), training history, nutritional status, and recovery capacity all cause the same program to produce different results in different individuals. The common “responder vs. low-responder” phenomenon in research reminds us that dosage must be individualized and continuously monitored with objective indicators (such as 1RM progress, RFD, time-trial performance). A practical principle is: establish a foothold at the minimum effective dose, then progressively increase through progressive overload, and decisively step back when signs of poor recovery or stagnant endurance performance appear.

Particularly in the context of concurrent training, the “ceiling” of dosage is often determined not by strength adaptation but by the degree to which it competes with endurance training for recovery resources. This is why elite endurance athletes typically use much more conservative strength training doses than pure strength athletes—they seek “sufficient” strength stimulus, not “maximal” strength stimulus.

Differences Across Populations

The benefits of strength training periodization models are not “one-size-fits-all”; population characteristics significantly moderate the direction and magnitude of adaptation.

Beginners vs. advanced athletes. For strength training novices, the rapid early progress comes almost entirely from neural adaptation, with benefits that are significant and easily obtained (the so-called “beginner gains”). However, for advanced athletes with years of training experience, the neural system’s “ceiling” is lower, and continued progress often requires more sophisticated periodization, higher intensity, or novel stimuli (such as eccentric overload or power-oriented approaches). Research shows that effect sizes for advanced athletes are typically smaller than for beginners, but because their performance is already near personal limits, even a 1–2% improvement can decide victory or defeat in competition.

Sex differences. Vikmoen et al.'s research on female road cyclists is particularly important because early literature focused mainly on males. Results show that women derive the same improvements in exercise economy and time-trial performance from strength training, and because women start from a lower relative muscle mass baseline, some studies have even observed greater relative room for improvement. Differences in hormonal environment (testosterone) between men and women primarily affect the absolute magnitude of hypertrophy, not the “direction” of neural and tendon adaptations.

Age differences. With advancing age, the loss of fast-twitch muscle fibers and motor units (sarcopenia) makes strength training shift from “icing on the cake” to “indispensable.” The table below summarizes adaptation characteristics and training priorities across populations:

Population	Adaptation Characteristics	Training Priorities
Beginners	Neural adaptation dominant, rapid progress	Build movement quality, progressive loading
Advanced athletes	Slower adaptation, need refined stimuli	Periodization, power/eccentric focus
Female athletes	Greater relative room for improvement	Same principles as males, avoid over-conservatism
Older athletes (>50)	Counteracting sarcopenia, neural loss	Maintain high-intensity stimulus, emphasize RFD
Adolescents	Prioritize movement technique and safety	Start with bodyweight, avoid early heavy loads

Understanding these differences allows athletes and coaches to avoid forcing a single program onto everyone and to make reasonable adjustments based on their own stage and conditions. It is worth noting that population categories are only a starting point; true individualization must return to each athlete’s response data.

Practical Training Application

Translating research into a training program requires answering four questions: which exercises to do, what intensity to use, when to schedule them, and how to monitor.

Exercise selection. For cycling and running, the most transferable exercises are multi-joint, closed-chain movements covering the hip-knee-ankle extension chain—squats, deadlifts, split squats, step-ups, and calf raises. For the specific goals of strength training periodization models, supplementary exercises (such as eccentric components, plyometric jumps, or core stability work) can be added accordingly.

Intensity and sets. When maximal strength is the primary goal, 4–6RM with 3–4 sets per exercise and rest intervals of 3 minutes or more between sets is recommended to ensure quality. If the goal leans toward power and RFD, lighter loads (30–60% 1RM) combined with “maximal velocity intent” should be used, as movement velocity itself is the stimulus. Below is a sample off-season weekly schedule:

Day	Main Training	Strength Program Example
Monday	Endurance (long aerobic)	—
Tuesday	Strength (maximal strength focus)	Squat 5×5, Romanian deadlift 4×6, calf raise 3×8
Wednesday	Endurance (tempo/threshold)	—
Thursday	Strength (power focus)	Jump squat 5×3, single-leg step-up 3×6, core circuit
Friday	Recovery/technique	—
Saturday	Long endurance or race simulation	—
Sunday	Complete rest	—

Scheduling. To reduce interference effects, if both types of training are performed on the same day, strength and high-intensity endurance sessions should be separated by at least 6 hours, or placed on different days; when they must be on the same day, prioritize the ability that is the current focus (strength first in the pre-season, endurance first in-season).

Monitoring indicators. Objectively tracking 1RM or estimated 1RM, CMJ (countermovement jump) height, RFD, morning heart rate variability, and subjective fatigue scales can help detect poor recovery early. When CMJ declines consecutively or time-trial performance stagnates, treat it as a signal to adjust dosage. Remember: strength training is the “auxiliary engine” for endurance performance—its purpose is to make you more efficient on the racecourse, not to lift heavier in the gym. Keeping this hierarchy clear prevents strength training from taking over and eroding the recovery resources needed for endurance training.

Local Application in Taiwan

Taiwan’s climate, terrain, and racing culture bring several unique considerations to the application of strength training periodization models.

Recovery management in hot, humid conditions. Taiwan’s summer heat and humidity can impede recovery after strength training due to dehydration and reduced sleep quality. It is recommended to schedule heavy lifting in the early morning or in air-conditioned indoor gyms, and to pay special attention to post-training hydration, electrolytes, and protein intake, avoiding stacking high-intensity endurance and strength stimuli on hot afternoons to prevent exacerbating interference effects.

Specific demands of climbing races. Classic Taiwanese events such as Wuling (west approach), the northern route to Wuling, and the Yangmingshan series (Fengguizui, Balaka) are known for long distances and massive elevation gain. These events place extremely high demands on “sustained output at low cadence and high torque,” which is precisely the scenario where maximal strength and single-leg strength training transfer directly. For challenges like Wuling with its ~3,000-meter elevation change, lower-body maximal strength reserves allow riders to maintain pedaling margin on the later steep sections, avoiding the dreaded “legs giving out first.”

Local training resources and seasonal rhythm. Gyms are widely available in most Taiwanese counties and cities, allowing cyclists to use the free-weight area for squats and deadlifts; those training at home can achieve similar stimuli with kettlebells, resistance bands, and bodyweight single-leg exercises. For cyclists whose main training grounds are Yangmingshan, Beiyi, and the Central Cross-Island Highway, it is recommended to concentrate a strength specialization block during the off-season (typically the hottest summer period, when long outdoor sessions are less suitable), turning the hot season into a golden window for building a strength foundation, then returning outdoors in the cooler autumn and winter to convert that strength into actual riding performance. In this way, Taiwan’s unique seasonal rhythm can combine perfectly with strength training periodization, becoming a strategic advantage for local athletes.

Common Myth-Busting

Many claims circulating about strength training periodization models contradict the academic evidence. Let us clarify them one by one.

Myth 1: “Lifting weights will make you bulky and heavy, hurting endurance.” Evidence shows that maximal-strength-oriented training (high intensity, low volume) primarily produces neural and tendon adaptations, with limited increases in muscle cross-sectional area; most studies show no significant change in body weight, while performance improves due to enhanced efficiency.

Myth 2: “Endurance athletes should only do high-rep, light-weight ‘muscular endurance’ training.” The opposite is true: high-rep, light-weight training provides insufficient stimulus for neural drive and tendon stiffness, and many studies indicate that heavy-load, low-rep training has better transfer benefits.

Myth 3: “Strength training effects will show up immediately in performance.” Although neural adaptations are fast, tendon remodeling and muscle fiber conversion take weeks to months; giving up too early is a common mistake.

Myth 4: “The interference effect of concurrent training will cancel out the benefits of strength training.” The interference effect does exist, but its magnitude depends heavily on training order, spacing, and dosage; with proper scheduling, strength and endurance can absolutely coexist and thrive. Dispelling these myths allows athletes to approach training with correct expectations and invest limited time and energy where it truly pays off.

Conclusion

Looking at the evidence reviewed in this article, strength training periodization models are no longer a question of “whether to do it” but “how to do it smarter.” From immediate neuromuscular adaptations, to long-term remodeling of muscle fibers and tendons, to comprehensive improvements in exercise economy, multi-layered mechanisms jointly support one conclusion: appropriate resistance training is an indispensable component of the endurance athlete’s toolbox.

Future research directions include predicting individual responses using genetic and molecular markers, clarifying the optimal molecular-level interval for concurrent training, and developing new resistance training equipment with greater sport specificity. For Taiwanese cyclists and runners, the most practical course of action is: build a solid maximal strength foundation in the off-season, maintain it with the minimum effective dose during the season, and monitor throughout with objective indicators, allowing strength to truly translate into speed and endurance on the racecourse. Science has pointed the way; what remains is putting it into practice with every squat and every stand.

Related Reading

• Effect of Strength Training Frequency on Muscle Hypertrophy: Meta-Analysis of 1 vs. 5 Sessions per Week
• Improvement of Running Economy Through Resistance Training: Dosage Recommendations from a Systematic Review
• Systematic Review of Periodized Training: Linear vs. Nonlinear vs. Undulating Periodization Comparison
• Nonlinear Loading Models in Training Periodization: Adaptive Advantages of Undulating Periods