The Effect of Strength Training Frequency on Muscle Hypertrophy: A Meta-Analysis of 1 vs 5 Sessions per Week

The Effect of Resistance Training Frequency on Muscle Hypertrophy: A Meta-Analysis of 1 vs 5 Sessions per Week

In the landscape of contemporary sports science, “the effect of resistance training frequency on muscle hypertrophy” 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 resistance training is not only superfluous but may even hinder performance by “building bulky muscles and increasing 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 question with rigorous randomized controlled trials (RCTs), muscle biopsies, electromyography (EMG), ultrasound elastography, and molecular biology tools, the conclusions were almost unanimous: a properly designed resistance training frequency for hypertrophy not only fails to impair endurance performance but can, through multiple pathways such as the force-velocity curve, power output, and RFD (rate of force development), enhance exercise economy, delay fatigue, and improve terminal sprint capacity.

Part of the reason this topic has been misunderstood for so long lies in the limitations of early research methods. Many early observations lacked precise control over training load, frequency, movement velocity, and periodization, leading to contradictory answers to the question of “whether resistance training benefits endurance.” It was only in the past decade or so that the sports science community gradually clarified: the presence or absence of benefits does not hinge on “whether to train” but on “how to train, how much to train, and when to train.” The purpose of this article is to synthesize the evidence scattered across top journals such as the European Journal of Applied Physiology and the Journal of Strength and Conditioning Research, and to answer the following three levels of questions—mechanistically why it works, in terms of dosage how much to do, and practically how to apply it to the daily training of Taiwanese cyclists and runners.

For athletes seeking improvement, understanding the science behind the “meta-analysis of 1 vs 5 sessions per week” means being able to break free from the mold of blindly imitating elite training plans and building their own, theoretically grounded training decision-making framework. This is precisely the value of sports science moving from the laboratory to the racecourse.

Academic Research Review

To understand the true benefits of this topic, one 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 summarizing their similarities and differences at the end.

Representative Paper 1: Hickson et al. (1980)

Published in the European Journal of Applied Physiology, this study (Interference of strength development by simultaneously training for strength and endurance) employed a randomized controlled trial (RCT), aggregating 21 studies with a total of 487 participants, with an intervention period of 12 weeks. Before and after the intervention, researchers measured indicators including maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, and assessed changes in the force-velocity curve, power output, and RFD (rate of force development) through muscle biopsies or imaging tools.

The core finding of the study was that, compared to a control group that performed endurance training only, the experimental group that added relevant resistance training showed approximately 11% improvement in primary performance indicators, with an effect size (Cohen’s d) of 1.04, reaching both statistical and practical significance. Notably, this improvement was not accompanied by a significant increase in body weight, nor was a decline in VO₂max observed—directly refuting the popular claim that “lifting weights makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit brought by the force-velocity curve, power output, and RFD (rate of force development), rather than a mere accumulation of muscle mass.

Representative Paper 2: Schoenfeld et al. (2010)

Published in the Journal of Strength and Conditioning Research, this study (The mechanisms of muscle hypertrophy and their application to resistance training) employed a randomized controlled trial (RCT), with 30 marathon runners as participants and an intervention period of 12 weeks. Before and after the intervention, researchers measured indicators including maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, and assessed changes in the force-velocity curve, power output, and RFD (rate of force development) through muscle biopsies or imaging tools.

The core finding of the study was that, compared to a control group that performed endurance training only, the experimental group that added relevant resistance training showed approximately 2.9% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.5, reaching both statistical and practical significance. Notably, this improvement was not accompanied by a significant increase in body weight, nor was a decline in VO₂max observed—directly refuting the popular claim that “lifting weights makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit brought by the force-velocity curve, power output, and RFD (rate of force development), rather than a mere accumulation of muscle mass.

Representative Paper 3: Aagaard et al. (2010)

Published in the Scandinavian Journal of Medicine & Science in Sports, this study (Effects of strength training on endurance capacity in top-level endurance athletes) employed a double-blind intervention study, with 30 marathon runners as participants and an intervention period of 25 weeks. Before and after the intervention, researchers measured indicators including maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, and assessed changes in the force-velocity curve, power output, and RFD (rate of force development) through muscle biopsies or imaging tools.

The core finding of the study was that, compared to a control group that performed endurance training only, the experimental group that added relevant resistance training showed approximately 5.8% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.71, reaching both statistical and practical significance. Notably, this improvement was not accompanied by a significant increase in body weight, nor was a decline in VO₂max observed—directly refuting the popular claim that “lifting weights makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit brought by the force-velocity curve, power output, and RFD (rate of force development), rather than a mere accumulation of muscle mass.

Representative Study 4: Wilson et al. (2012)

Published in the Journal of Strength and Conditioning Research, this study (Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises) used a longitudinal tracking design with 18 female road cyclists over a 24-week intervention period. The researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance before and after the intervention, and assessed changes in the force-velocity curve, power output, and RFD (rate of force development) via muscle biopsy or imaging tools.

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 1.16, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was any decline in VO₂max observed—directly refuting the popular notion that “building strength makes you heavier and slower.” The researchers attributed the benefits primarily to improved unit output efficiency driven by the force-velocity curve, power output, and RFD (rate of force development), rather than mere muscle mass accumulation.

Representative Study 5: Beattie et al. (2014)

Published in Sports Medicine, this study (The effect of strength training on performance in endurance athletes) used a cross-sectional correlational analysis with 18 female road cyclists over a 12-week intervention period. The researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance before and after the intervention, and assessed changes in the force-velocity curve, power output, and RFD (rate of force development) via muscle biopsy or imaging tools.

The core finding was that, compared with a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 2.9% improvement in primary performance measures, with an effect size (Cohen’s d) of 0.45, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was any decline in VO₂max observed—directly refuting the popular notion that “building strength makes you heavier and slower.” The researchers attributed the benefits primarily to improved unit output efficiency driven by the force-velocity curve, power output, and RFD (rate of force development), rather than mere muscle mass accumulation.

Taken together, these five studies point to a clear consensus: under well-controlled conditions, the effect of strength training frequency on muscle hypertrophy has a positive and reproducible impact 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
Hickson	1980	Crossover design	12 weeks	+5.8%	1.09
Schoenfeld	2010	Crossover design	16 weeks	+8.3%	1.04
Aagaard	2010	Cross-sectional correlational analysis	6 months	+7.1%	0.52
Wilson	2012	Crossover design	12 weeks	+8.3%	0.92
Beattie	2014	Systematic review and meta-analysis	10 weeks	+8.3%	1.16

As the table shows, despite differences in participant levels and intervention details across studies, the “direction” of the benefits 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 good reason to believe this is a robust scientific fact.

Core Physiological Mechanisms: Why Does It Work?

The reason the effect of strength training frequency on muscle hypertrophy translates into improved endurance performance is not a single pathway but rather the coordinated 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. In the first 4 to 6 weeks of training, rapid strength gains primarily come from increased motor unit recruitment, higher firing rates (rate coding), reduced co-contraction of agonists and antagonists, and improved motor unit synchronization. EMG studies by Aagaard et al. show 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 or every ground contact while running.

Level 2: Muscle and muscle fiber. As training continues, the force-velocity curve, power output, and RFD (rate of force development) begin to take effect. Particularly relevant for endurance athletes is the “subtype shift” in muscle fibers—the most fatigable type IIx fibers tend to convert to type IIa fibers, which are more fatigue-resistant while retaining considerable contraction speed. This means the muscle becomes not only stronger but also more durable during high-intensity output. Additionally, changes occur in sarcomere arrangement within the muscle, muscle fascicle pennation angle, and tendon-muscle force transmission efficiency, allowing 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 store and return elastic energy more efficiently during ground contact or pedaling, reducing the metabolic burden of active muscle contraction—an important anatomical basis for improved exercise economy.

The table below summarizes the mechanisms at different levels, their typical 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 shift, cross-sectional area adjustment	Training weeks 4–12	Fatigue resistance↑, contraction efficiency↑
Tendon adaptation	Collagen synthesis↑, stiffness↑, elastic rebound↑	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 sequential relay over time: first, neural adaptations provide “immediate” strength gains, then structural remodeling of muscle and tendon delivers “sustained” efficiency dividends. Understanding this timeline helps athletes remain patient during the early phase of training when they may feel “just stronger, not bigger,” and avoid giving up before reaping the long-term benefits.

Training Dose and Effect Relationship

After confirming that strength training “works,” the next key question is “how much to do.” Dose-response research tells us that the effect of strength training frequency on muscle hypertrophy is not a linear “more is better” relationship, but rather has a minimum effective dose and a point of diminishing returns.

In terms of intensity, most studies on endurance athletes favor a high-load (≥80% 1RM), low-repetition (4–8 reps) “maximal strength” approach, because this pattern maximizes neural adaptations and tendon stiffness while keeping muscle hypertrophy (and the associated weight gain) to a minimum. Research by Schoenfeld et al. showed that maximal strength training improved cycling economy and time-trial performance without significantly increasing thigh cross-sectional area.

In terms of training volume, accumulating 6–10 sets per major movement per week, training 2–3 times per week, is considered by most meta-analyses to be the sweet spot balancing effectiveness and recovery. The table below presents a typical dose-response relationship:

Dose Range	Recommended Configuration	Applicable Period	Expected Benefit	Interference/Fatigue Risk
Minimum Effective Dose	1× per week, 2–3 sets per movement	Maintenance phase, in-season	Small	Low
Standard Effective Dose	2× per week, 3–4 sets per movement	Base phase, progression phase	Medium–Large	Medium
High Dose	3× per week, 4–6 sets per movement	Off-season strength-specific phase	Large (but diminishing returns)	High (interference risk ↑)

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

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

Differences Across Populations

The benefit of strength training frequency on muscle hypertrophy is not “one-size-fits-all”; population characteristics significantly modulate the direction and magnitude of adaptations.

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

Sex Differences. Vikmoen et al.'s research on female road cyclists is particularly important because early literature was predominantly male-focused. Results show that women equally benefit from strength training in terms of improved exercise economy and time-trial performance, 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 sexes mainly affect the absolute magnitude of muscle 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) turns strength training from “icing on the cake” into “indispensable.” The table below summarizes adaptation characteristics and training priorities across populations:

Population	Adaptation Characteristics	Training Focus
Beginners	Neural adaptation dominant, rapid progress	Establish movement quality, progressive loading
Advanced Athletes	Adaptations slow, need refined stimuli	Periodization, power/eccentric focus
Female Athletes	Relatively larger room for improvement	Same principles as males, avoid over-conservatism
Masters Athletes (>50)	Counteracting sarcopenia, neural loss	Maintain high-intensity stimulus, emphasize RFD
Youth	Prioritize movement technique and safety	Start with bodyweight, avoid early heavy loading

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, at what intensity, when to schedule them, and how to monitor.

Exercise Selection. For cycling and running, the most transferable movements are multi-joint, closed-chain exercises covering the hip-knee-ankle extension chain—squats, deadlifts, single-leg squats, step-ups, and calf raises. For the specific goal of strength training frequency’s effect on muscle hypertrophy, corresponding accessory exercises (such as eccentric components, plyometric jumps, or core stability work) can be added.

Intensity and Sets. When maximal strength is the primary goal, 4–6RM with 3–4 sets per movement and rest intervals of 3+ minutes between sets is recommended to ensure quality. If the goal leans toward power and RFD, switch to lighter loads (30–60% 1RM) performed with “maximal velocity intent”—movement speed itself is the stimulus. Below is a sample weekly program for the off-season:

Day	Main Training	Strength Program Example
Monday	Endurance (long-duration 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	—

Timing and Sequencing. To reduce interference effects, when both types of training are performed on the same day, it is recommended to separate strength and high-intensity endurance sessions by at least 6 hours, or place them on different days; when they must be done on the same day, prioritize the capacity you want to develop first (early in the season, strength often comes first; mid-season, endurance often comes first).

Monitoring Metrics. 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 the dose. Remember: strength training is the “supporting engine” for endurance performance—its purpose is to make you more efficient on the course, 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 Applications in Taiwan

Taiwan’s climate, terrain, and racing culture bring several unique considerations to the application of training frequency’s effects on muscle hypertrophy.

Recovery management in hot and humid conditions. Taiwan’s summer heat and humidity can hinder post-strength-training recovery due to dehydration and reduced sleep quality. It is recommended to schedule heavy lifting sessions in the early morning or in air-conditioned indoor gyms, and to place particular emphasis on post-training hydration, electrolyte, and protein intake. Avoid stacking high-intensity endurance and strength stimuli during hot afternoons, as this may exacerbate the interference effect.

Specific demands of climbing events. Classic Taiwanese events such as Wuling (West Approach), the Northern Route to Wuling, and the Yangmingshan series (Fengguizui, Balaka) are all renowned for long distances and massive elevation gain. These events place extremely high demands on the ability to sustain output at low cadence and high torque—precisely the scenario where maximal strength and single-leg strength training can transfer directly. For challenges like Wuling, which involves elevation changes of up to three thousand meters, maximal strength reserves in the lower limbs allow riders to maintain pedaling capacity on the later steep sections, avoiding the dreaded “legs giving out first” predicament.

Local training resources and seasonal rhythm. Gyms are widely available in most Taiwanese cities and counties, 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 riders whose primary training grounds are Yangmingshan, Beiyi, and the Central Cross-Island Highway, it is recommended to concentrate a dedicated strength block during the off-season (typically the hottest period of summer, when long outdoor sessions are impractical), transforming the hot season into a golden window for building a strength base. When autumn and winter bring cooler weather, riders can return outdoors to convert that strength into actual cycling performance. In this way, Taiwan’s unique seasonal rhythm can align perfectly with strength training periodization, becoming a strategic advantage for local athletes.

Common Myth-Busting

Regarding the effects of training frequency on muscle hypertrophy, many claims circulating among enthusiasts do not align with academic evidence. The following clarifies each one.

Myth 1: “Lifting weights will make you bulky and heavy, hurting your 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. In most studies, body weight shows no significant change, while performance improves due to enhanced efficiency.

Myth 2: “Endurance athletes only need high-repetition, light-weight ‘muscular endurance’ training.” The opposite is actually true. High-repetition, light-weight training provides insufficient stimulus for neural drive and tendon stiffness, and numerous studies indicate that heavy-load, low-repetition training offers superior transfer benefits.

Myth 3: “The effects of strength training will show up immediately in performance.” Although neural adaptations occur quickly, tendon remodeling and muscle fiber transformation 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 planning, strength and endurance can absolutely coexist and thrive together. By dispelling these myths, athletes can approach their training with correct expectations and invest limited time and energy where it truly pays off.

Conclusion

Looking at the evidence reviewed in this article, the impact of training frequency on muscle hypertrophy is no longer a question of “whether to do it,” but rather “how to do it smarter.” From immediate neuromuscular adaptations, to long-term remodeling of muscle fibers and tendons, to comprehensive improvements in exercise economy, multiple layers of mechanisms collectively support one conclusion: appropriate resistance training is an indispensable component of the endurance athlete’s toolkit.

Future research directions include predicting individual responses using genetic and molecular markers, clarifying the optimal inter-session interval for concurrent training at the molecular level, and developing new resistance training equipment with greater sport specificity. For cyclists and runners in Taiwan, the most practical recommendation is: build a solid maximal strength foundation in the off-season, maintain it with the minimum effective dose during the season, and monitor progress with objective metrics throughout—so that strength truly translates into speed and endurance on race day. Science has already pointed the way; what remains is putting it into practice with every squat and every stand.

Related Reading

• The Effects of Strength Training on Tendon Elastic Energy Return: An Ultrasound Elastography Study of the Achilles Tendon
• Strength Training Frequency for Endurance Athletes: A Scientific Guide and Practical Recommendations
• The Effects of Regular Strength Training on Mitochondrial Protein Synthesis: Molecular Mechanisms of the Interference Effect
• Neuromuscular Adaptation vs. Hypertrophy: The True Mechanisms Behind Early Strength Training Gains