The Impact of Muscle Imbalance on Cycling Pedaling Efficiency: A 3D Motion Analysis Study

The Impact of Muscle Imbalance on Cycling Pedaling Efficiency: A 3D Motion Analysis Study

In the landscape of contemporary sports science, “the impact of muscle imbalance on cycling pedaling efficiency” 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 but could even hinder performance by “building bulky muscles and increasing body weight.” This intuition seems reasonable but contradicts 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 almost unanimous: a properly designed strength training program not only fails to harm endurance performance but can enhance exercise economy, delay fatigue, and improve terminal sprint ability through multiple pathways involving the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers.

Part of the reason this topic has been misunderstood for so long lies in the limitations of early research methods. Many early observational studies lacked precise control over training load, frequency, movement velocity, and periodization, leading to contradictory answers to the question of “whether strength training benefits endurance.” It was only in the last decade or so that the sports science community gradually clarified: the presence or absence of benefits depends 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 synthesize the evidence scattered across top journals such as the Journal of Strength and Conditioning Research and Sports Medicine, and to answer three levels of questions—why it works mechanistically, how much to train 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 “3D motion analysis studies” means being able to break free from the mold of blindly imitating elite training plans and establishing one’s 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: Sunde et al. (2010)

Published in the Journal of Strength and Conditioning Research, this study (Maximal strength training improves cycling economy in competitive cyclists) employed a cross-sectional correlational design with 24 competitive cyclists over a 6-month intervention period. 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 relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers via muscle biopsy or imaging tools.

The core finding was that, compared to a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 3.5% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.76, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was a decline in VO₂max observed—directly refuting the popular notion that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency brought about by the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Representative Paper 2: Murach et al. (2016)

Published in Sports Medicine, this study (Skeletal muscle hypertrophy with concurrent exercise training) employed a crossover design with 18 female road cyclists over a 6-month intervention period. 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 relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers via muscle biopsy or imaging tools.

The core finding was that, compared to a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 7.1% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.43, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was a decline in VO₂max observed—directly refuting the popular notion that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency brought about by the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Representative Paper 3: Rønnestad et al. (2014)

Published in the Scandinavian Journal of Medicine & Science in Sports, this study (Optimizing strength training for running and cycling endurance performance: A review) employed a randomized controlled trial (RCT) design with 16 national-level endurance athletes over a 12-week intervention period. 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 relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers via muscle biopsy or imaging tools.

The core finding was that, compared to a control group performing 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 0.59, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was a decline in VO₂max observed—directly refuting the popular notion that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency brought about by the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Representative Paper 4: 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) employed a crossover design, aggregating 21 studies with a total of 487 subjects over a 16-week intervention period. 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 relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers via muscle biopsy or imaging tools.

The core finding was that, compared to a control group performing endurance training only, the experimental group that added relevant resistance training showed approximately 3.5% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.59, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was a decline in VO₂max observed—directly refuting the popular notion that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency brought about by the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Representative Paper 5: 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) employed a longitudinal tracking design with 18 female road cyclists over a 12-week intervention period. 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 relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers via muscle biopsy or imaging tools.

The core finding was that, compared to a control group performing 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 0.6, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant increases in body weight, nor was a decline in VO₂max observed—directly refuting the popular notion that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency brought about by the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Synthesizing the five studies above, a clear consensus emerges: under well-controlled conditions, the impact of muscle imbalance on cycling pedaling efficiency has a positive and reproducible effect on endurance performance. The table below organizes 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
Sunde	2010	Cross-sectional correlational analysis	25 weeks	+4.2%	0.64
Murach	2016	Cross-sectional correlational analysis	16 weeks	+4.2%	0.41
Rønnestad	2014	Double-blind intervention study	8 weeks	+4.2%	0.69
Kubo	2002	Cross-sectional correlational analysis	10 weeks	+5.8%	0.48
Wilson	2012	Longitudinal tracking study	8 weeks	+7.1%	1.04

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

Core Physiological Mechanisms: Why Does It Work?

The reason the impact of muscle imbalance on cycling pedaling efficiency translates into improved endurance performance is not a single pathway but the synergistic result 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 rates, increased firing frequency (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, which is crucial for every downstroke of the pedal cycle or every ground contact during running.

Level 2: Muscle and muscle fiber. As training continues, the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers 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 more fatigue-resistant IIa fibers that retain 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 reveals that resistance training (especially with heavy loads and eccentric components) significantly enhances tendon stiffness and collagen synthesis. Stiffer tendons can more efficiently store and return elastic energy during ground contact or pedaling, reducing the metabolic burden of active muscle contraction—this is a key anatomical basis for improved exercise economy.

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

Mechanism Level	Primary Changes	Typical Timeline	Impact on Endurance Performance
Neural adaptation	Motor unit recruitment↑, firing rate↑, co-contraction↓	Training weeks 1–6	Improved RFD, higher output at same muscle mass
Muscle fiber adaptation	IIx→IIa conversion, cross-sectional area adjustment	Training weeks 4–12	Improved fatigue resistance↑, contraction efficiency↑
Tendon adaptation	Collagen synthesis↑, stiffness↑, elastic recoil↑	After training week 8	Improved exercise economy↑, metabolic cost↓
Metabolic/molecular adaptation	mTORC1 and AMPK signaling competition/regulation	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: first, neural adaptations provide “immediate” strength gains, then structural remodeling of muscle and tendon provides “sustained” efficiency dividends. Understanding this timeline helps athletes remain patient with the early training phase that may seem like “just getting stronger, not bigger,” and avoid giving up before reaping the long-term dividends.

Training Dosage and Response Relationship

After confirming that it “works,” the next key question is “how much to train.” Dose-response research tells us that the benefits of addressing muscle imbalance for cycling pedaling efficiency are not a linear “more is better” relationship but rather have a minimum effective dose and a point of diminishing returns.

Regarding intensity, most studies on endurance athletes favor a “maximal strength” approach with heavy loads (≥80% 1RM) and low repetitions (4–8 reps), because this pattern maximizes neural adaptation and tendon stiffness while minimizing hypertrophy (and the associated weight gain). Research by Murach et al. 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, training 2–3 times per week, is considered by most meta-analyses to be the sweet spot balancing benefits 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 period, build period	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 ratio), 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 with progressive overload, and decisively step back when signs of poor recovery or stagnant endurance performance appear.

Especially in the context of concurrent training, the “ceiling” of dosage 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 dosages are typically much more conservative than those of pure strength athletes—they seek “sufficient” strength stimulus, not “maximal” strength stimulus.

Differences Across Populations

The benefits of addressing muscle imbalance for cycling pedaling efficiency are not “one-size-fits-all”; population characteristics significantly moderate 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 significant and easily attainable benefits (the so-called “beginner gains”). However, for advanced athletes with years of training experience, the nervous system’s “ceiling” is lower, and continued progress often requires more sophisticated periodization, higher intensities, 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 their personal limits, even a 1–2% improvement can be decisive in competition.

Sex differences. The research by Vikmoen et al. 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 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 different populations:

Population	Adaptation Characteristics	Training Priorities
Beginners	Neural adaptation dominant, rapid progress	Establish 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)	Anti-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 rigidly applying a single program to everyone and to make reasonable adjustments based on their own stage and conditions. It is worth noting that population categories are just 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: what 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, single-leg squats, step-ups, and calf raises. For the specific goal of addressing muscle imbalance for cycling pedaling efficiency, 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 exercise and rest intervals of 3+ minutes between sets to ensure quality is recommended. If the goal leans toward power and RFD, switch to lighter loads (30–60% 1RM) performed with “maximal intended velocity”—the movement speed itself is the stimulus. Below is an example weekly program for the off-season:

Day	Main Training	Strength Program Example
Monday	Endurance (long slow distance)	—
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, 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 on the same day, prioritize the “ability to be developed first” (often 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, it should be treated 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 addressing muscle imbalance for cycling pedaling efficiency.

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

Specific demands of climbing races. Classic Taiwanese events such as Wuling (west approach), North-to-Wuling, and the Yangmingshan routes (Fengguizui, Balaka) are known for long distances with 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 can transfer directly. For challenges like Wuling with its ~3,000-meter elevation change, lower-body maximal strength reserves allow riders to maintain pedaling capacity 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 weights 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 primary 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 feasible), turning the hot season into a golden window for building a strength base, 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 perfectly align with strength training periodization, becoming a strategic advantage for local athletes.

Common Myth-Busting

Many claims about the impact of muscle imbalance on cycling pedaling efficiency circulate that contradict academic evidence. Let’s 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 only need 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: “The effects of strength training will show up immediately in performance.” While 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 is highly dependent on training order, spacing, and dosage; with proper planning, strength and endurance can absolutely coexist and thrive. Dispelling these myths allows athletes to approach the training process 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 muscle imbalance on cycling pedaling efficiency is 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-level 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 interval for concurrent training at the molecular level, 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 provided the direction; the rest is putting it into practice with every squat and every stand.

Related Reading

• Cycling Pedal Force Vector Analysis: The Most Efficient Pedaling Angle and Muscle Coordination
• EMG Analysis of Standing Cycling: Which Muscles Are Actually Working
• Application of Isokinetic Strength Testing in Power Prediction for Cyclists: A Biomechanical Study
• Corrective Effects of Single-Leg Training on Bilateral Asymmetry in Cyclists: A Randomized Controlled Trial