The Impact of Strength Training on Running Ground Reaction Forces: A Biomechanical Adaptation Study

The Impact of Strength Training on Running Ground Reaction Forces: A Biomechanical Adaptation Study

In the landscape of contemporary sports science, “the impact of strength training on running ground reaction forces” 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 may even hinder performance by “building bulky muscles and increasing body weight.” This intuition seems reasonable on the surface, 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 does not harm endurance performance in terms of its impact on running ground reaction forces. Instead, through multiple pathways—including tendon collagen synthesis, stiffness, and elastic energy storage and return—it can improve exercise economy, delay fatigue, and enhance end-stage sprinting ability.

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 not until the past decade or so that the sports science community gradually clarified: whether benefits exist does not hinge on “whether to train” but on “how to train, how much, and when.” The purpose of this article is to synthesize the evidence scattered across top journals such as the Scandinavian Journal of Medicine & Science in Sports and the Journal of Strength and Conditioning Research, 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 “biomechanical adaptation studies” means being able to break free from the trap of blindly imitating elite training plans and to build 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 at the end summarizing their similarities and differences.

Representative Paper 1: 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 systematic review and meta-analysis, aggregating 21 studies with a total of 487 participants, with an intervention period of 12 weeks. Before and after the intervention, the 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 tendon collagen synthesis, stiffness, and elastic energy storage and return.

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 indicators, with an effect size (Cohen’s d) of 0.43, 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 “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit from tendon collagen synthesis, stiffness, and elastic energy storage and return, rather than a mere accumulation of muscle mass.

Representative Paper 2: 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 longitudinal tracking design with 20 amateur cyclists as participants and an intervention period of 8 weeks. Before and after the intervention, the 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 tendon collagen synthesis, stiffness, and elastic energy storage and return.

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 indicators, with an effect size (Cohen’s d) of 0.42, 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 “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit from tendon collagen synthesis, stiffness, and elastic energy storage and return, rather than a mere accumulation of muscle mass.

Representative Paper 3: 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 cross-sectional correlational analysis with 24 categorized cyclists as participants and an intervention period of 16 weeks. Before and after the intervention, the 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 tendon collagen synthesis, stiffness, and elastic energy storage and return.

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 indicators, with an effect size (Cohen’s d) of 1.02, 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 “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved output efficiency per unit from tendon collagen synthesis, stiffness, and elastic energy storage and return, rather than a mere accumulation of muscle mass.

Representative Study 4: Hawley et al. (2009)

Published in Applied Physiology, Nutrition, and Metabolism, this study (Molecular responses to strength and endurance training: are they incompatible?) employed a cross-sectional correlational analysis involving 24 graded cyclists 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, while also assessing changes in tendon collagen synthesis, stiffness, and elastic energy storage and return 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 5.8% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.84, achieving 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 primarily attributed the benefits to improved output efficiency from tendon collagen synthesis, stiffness, and elastic energy storage and return, rather than mere muscle mass accumulation.

Representative Study 5: 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 systematic review and meta-analysis, aggregating 21 studies with a total of 487 participants over a 25-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, while also assessing changes in tendon collagen synthesis, stiffness, and elastic energy storage and return 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 5.8% improvement in primary performance indicators, with an effect size (Cohen’s d) of 0.44, achieving 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 primarily attributed the benefits to improved output efficiency from tendon collagen synthesis, stiffness, and elastic energy storage and return, rather than mere muscle mass accumulation.

Taken together, the five studies above converge on a clear consensus: under well-controlled conditions, the effect of strength training on ground reaction forces in running 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
Rønnestad	2014	Crossover design	12 weeks	+4.2%	0.74
Sunde	2010	Double-blind intervention study	10 weeks	+8.3%	1.15
Schoenfeld	2010	Systematic review and meta-analysis	6 months	+7.1%	0.65
Hawley	2009	Randomized controlled trial (RCT)	16 weeks	+8.3%	0.54
Aagaard	2010	Crossover design	16 weeks	+5.8%	1.18

As the table shows, despite differences in participant levels and intervention details across studies, the “direction” of the benefits is highly consistent—a key indicator of evidence strength. A single study may be influenced by sample and design factors, 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 translation of strength training’s effect on ground reaction forces in running into improved endurance performance does not follow a single pathway but results 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 primarily stem 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 cycle or every push-off in running.

Level 2: Muscle and muscle fiber. As training continues, tendon collagen synthesis, stiffness, and elastic energy storage and return begin to take effect. Particularly crucial 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 occur in sarcomere arrangement, 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 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 push-off or pedaling, reducing the metabolic burden of active muscle contraction—this is the key anatomical basis for improved exercise economy.

The table below summarizes the mechanisms at different levels, their typical 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 adjustments	Training weeks 4–12	Improved fatigue resistance↑, contraction efficiency↑
Tendon adaptation	Collagen synthesis↑, stiffness↑, elastic return↑	After training week 8	Improved exercise economy↑, lower metabolic cost↓
Metabolic/molecular adaptation	mTORC1 and AMPK signaling competition and 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 operate in a temporal relay: first, neural adaptations provide “immediate” strength gains, followed by structural remodeling of muscle and tendon that delivers “lasting” efficiency dividends. Understanding this timeline helps athletes remain patient with the early-training phenomenon of “just getting stronger, not bigger,” and avoid giving up before reaping the long-term dividends.

Training Dose and Effect Relationship

After confirming “effectiveness,” the next key question is “how much to train.” Dose-response research tells us that the benefits of strength training are not a linear “more is better” relationship, but rather there is a minimum effective dose and a point of diminishing returns.

In terms of intensity, most studies targeting endurance athletes favor a “maximal strength” approach with high loads (≥80% 1RM) and low repetitions (4–8 reps), because this pattern maximizes neural adaptation and tendon stiffness while keeping hypertrophy (and the associated weight gain) to a minimum. Research by Sunde 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, with 2–3 sessions 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:

Dose Range	Recommended Configuration	Applicable Phase	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, build 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 a major 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: dosage must be individually adjusted and continuously monitored with objective metrics (such as 1RM progression, RFD, time-trial performance). A practical principle is: after establishing a solid footing at the minimum effective dose, progressively increase with 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 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’ 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 benefits of strength training are not “one-size-fits-all”; population characteristics significantly modulate 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 “newbie gains”). However, for advanced athletes with years of training background, the neural system’s “ceiling” is lower, and continued progress often requires more sophisticated 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. The research by Vikmoen et al. on female road cyclists is particularly important because earlier literature was predominantly male-focused. Results show that women similarly achieve improvements in exercise economy and time-trial performance from strength training, and because women’s relative muscle mass starts from a lower baseline, some studies even observe 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 adaptation.

Age Differences. With advancing age, the loss of fast-twitch muscle fibers and motor units (sarcopenia) transforms strength training 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	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)	Counteract sarcopenia, neural loss	Maintain high-intensity stimulus, emphasize RFD
Adolescents	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 individual stage and conditions. It is worth noting that population classification is only a starting point; true individualization must still return to each athlete’s response data.

Practical Training Application

Translating research into a 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 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 specific goals, additional auxiliary exercises (such as eccentric components, plyometric jumps, or core stability training) can be incorporated.

Intensity and Sets. When maximal strength is the primary goal, 4–6RM with 3–4 sets per movement and rest intervals of 3 minutes or more 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”—the movement speed itself is the stimulus. Below is an example 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, when performing both types of training on the same day, 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 to be developed first” (often strength first in the pre-season, endurance first in-season).

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 dosage. Remember: strength training is the “auxiliary 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 strength training’s effects on running ground reaction forces.

Recovery management in hot, humid conditions. Taiwan’s summer heat and humidity can hinder recovery after strength training 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 can 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 roughly 3,000 meters of elevation change, 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” situation.

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 part 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 distinctive seasonal rhythm can be perfectly integrated with strength training periodization, becoming a strategic advantage for local athletes.

Common Myth-Busting

Many claims circulating about strength training’s effects on running ground reaction forces do not align with the academic evidence. The following clarifies each one.

Myth 1: “Lifting weights will make you bulky and heavy, dragging down 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 truth is the opposite. 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 effects.

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. 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 question of strength training’s effects on running ground reaction forces is no longer “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 toolkit.

Future research directions include using genetic and molecular markers to predict individual responses, clarifying the optimal molecular-level spacing for concurrent training, and developing new resistance training equipment with greater sport specificity. For cyclists and runners in Taiwan, 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 metrics—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

• Improvements in Running Economy from Resistance Training: Dosage Recommendations from a Systematic Review
• Insufficient Gluteal Activation in Running: Research on Gluteal Training for Running Injury Prevention
• The Effect of Strength Training on Tendon Elastic Energy Return: An Ultrasound Elastography Study of the Achilles Tendon
• The Influence of Maximal Strength on Endurance Performance: A Correlational Study of Peak Force and Cycling Efficiency