Time-Course Study of mTORC1 Activation Following a Single Heavy Resistance Training Session

Temporal Study of Single-Session Heavy-Load Training on mTORC1 Activation

In the landscape of contemporary exercise science, the “temporal study of single-session heavy-load training on mTORC1 activation” is one of the core issues spanning strength and conditioning, exercise physiology, and biomechanics. For a long time, a deeply ingrained belief has prevailed 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, 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: a properly designed single-session heavy-load training protocol for studying mTORC1 activation not only fails to impair endurance performance but can, through multiple pathways such as exercise economy, metabolic cost per unit output, and muscle efficiency, improve exercise economy, delay fatigue, and enhance 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 strength training benefits endurance performance.” It was not until the past decade or so that the exercise science community gradually clarified: whether benefits exist 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 integrate the evidence scattered across top journals such as the Journal of Strength and Conditioning Research and the Journal of Physiology 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 the “temporal study of single-session heavy-load training on mTORC1 activation” means being able to break free from the mold of blindly imitating elite training plans and to build their own, theoretically grounded training decision-making framework. This is precisely the value of exercise science moving from the laboratory to the racecourse.

Academic Literature 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 broken down 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: 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 systematic review and meta-analysis, involving 20 amateur cyclists as participants, with an intervention period of 10 weeks. 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 assessing changes in exercise economy, metabolic cost per unit output, and muscle efficiency through muscle biopsies or imaging tools.

The core finding of the study 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 indicators, with an effect size (Cohen’s d) of 0.62, 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 claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved 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) employed a cross-sectional correlational analysis, aggregating 21 studies with a total of 487 participants, with an intervention period of 8 weeks. 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 assessing changes in exercise economy, metabolic cost per unit output, and muscle efficiency through muscle biopsies or imaging tools.

The core finding of the study 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 0.7, 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 claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 3: Mujika et al. (2016)

Published in the International Journal of Sports Physiology and Performance, this study (Effects of increased muscle strength and muscle mass on endurance-cycling performance) employed a longitudinal follow-up design, involving 30 marathon runners as participants, with an intervention period of 16 weeks. 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 assessing changes in exercise economy, metabolic cost per unit output, and muscle efficiency through muscle biopsies or imaging tools.

The core finding of the study 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 indicators, with an effect size (Cohen’s d) of 0.62, 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 claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Paper 4: Coffey et al. (2007)

Published in Sports Medicine, this study (The molecular bases of training adaptation) employed a systematic review and meta-analysis, involving 18 female road cyclists as participants, with an intervention period of 8 weeks. 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 assessing changes in exercise economy, metabolic cost per unit output, and muscle efficiency through muscle biopsies or imaging tools.

The core finding of the study was that, compared with 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 1.0, 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 claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven by exercise economy, metabolic cost per unit output, and muscle efficiency, rather than mere muscle mass accumulation.

Representative Study 5: Andersen et al. (2005)

Published in the Journal of Applied Physiology, this study (Changes in the human muscle force-velocity relationship in response to resistance training and detraining) employed a longitudinal tracking design with 24 competitive cyclists as participants, and an intervention period of 16 weeks. 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 exercise economy, metabolic cost per unit output, and muscle efficiency through muscle biopsies or imaging tools.

The core finding of the study was that, compared with 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 0.57, 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 claim that “building strength makes you heavier and slower.” The researchers attributed the benefits primarily to improvements in exercise economy, metabolic cost per unit output, and muscle efficiency leading to enhanced output efficiency per unit, rather than mere accumulation of muscle mass.

Synthesizing the five studies above, a clear consensus emerges: under well-controlled conditions, the time-course research on single-session heavy-load training’s activation of mTORC1 shows a positive and reproducible effect on endurance performance. The table below summarizes the design and results of these studies across key variables, allowing readers to quickly compare their similarities and differences.

First Author	Year	Study Design	Intervention Period	Primary Benefit	Effect Size d
Sunde	2010	Double-blind intervention study	8 weeks	+7.1%	0.77
Kubo	2002	Double-blind intervention study	10 weeks	+5.8%	0.51
Mujika	2016	Double-blind intervention study	12 weeks	+7.1%	0.95
Coffey	2007	Longitudinal tracking study	8 weeks	+5.8%	0.74
Andersen	2005	Double-blind intervention study	12 weeks	+3.5%	0.84

As can be seen from the table, although the studies differ in participant level and intervention details, 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 reason to believe this is a robust scientific fact.

Core Physiological Mechanisms: Why Does It Work?

The reason the time-course research on single-session heavy-load training’s activation of mTORC1 translates into improved endurance performance is not a single pathway, but rather the synergistic result of multiple physiological levels. Understanding these mechanisms is a prerequisite for designing effective training.

Level 1: Neuromuscular level. The earliest adaptations from resistance training occur in the nervous system rather than in the muscle itself. During the first 4 to 6 weeks of training, rapid strength gains primarily stem from increased motor unit recruitment, increased firing frequency (rate coding), reduced co-contraction of agonists and antagonists, and improved motor unit synchronization. EMG studies by Aagaard et al. 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 phase of pedaling or every push-off in running.

Level 2: Muscle and muscle fiber level. As training continues, exercise economy, metabolic cost per unit output, and muscle efficiency begin to take effect. Particularly crucial for endurance athletes is the “subtype shift” of 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 become not only stronger but also more durable during high-intensity output. Additionally, changes occur in the arrangement of sarcomeres within muscles, muscle fascicle pennation angle, and tendon-muscle force transmission efficiency, allowing the same metabolic input 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 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 an important anatomical basis for improved exercise economy.

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

Mechanism Level	Primary Changes	Typical Time Course	Effect on Endurance Performance
Neural adaptation	Motor unit recruitment↑, firing frequency↑, co-contraction↓	Training weeks 1–6	RFD improved, 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 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 follow a relay relationship in temporal sequence: first, neural adaptations provide “immediate” strength gains, followed by structural remodeling of muscle and tendon delivering “sustained” 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 that it “works,” 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 on endurance athletes favor a high-load (≥80% 1RM), low-repetition (4–8 reps) “maximal strength” approach, because this pattern maximizes neural adaptation and tendon stiffness while keeping hypertrophy (and the associated weight gain) to a minimum. Research by Kubo 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 benefit 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, 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 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 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 foothold at the minimum effective dose, progressively increase with progressive overload, and decisively step back when poor recovery or stagnation in endurance performance appears.

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 “beginner gains”). However, for advanced athletes with years of training foundation, 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 early literature focused predominantly on males. 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 sexes 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) 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 dominates, rapid progress	Establish movement quality, progressive loading
Advanced Athletes	Adaptation slows, requires 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 categories are only a starting point; true individualization must still 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 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 accessory exercises can be incorporated (such as eccentric components, plyometric jumps, or core stability training).

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) combined with “maximal intended velocity” execution—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 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 of endurance training.

Local Applications in Taiwan

Taiwan’s climate, terrain, and racing culture bring several unique considerations to the application of research on the time course of mTORC1 activation following a single heavy resistance training session.

Recovery management in hot, humid conditions. Taiwan’s summers are characterized by high heat and humidity, and recovery after strength training can be hindered by dehydration and impaired sleep quality. It is recommended to schedule heavy training sessions in the early morning or in air-conditioned indoor gyms, with particular attention to 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 renowned for their 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 predicament of “legs giving out first.”

Local training resources and seasonal rhythm. Gyms are widely accessible 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 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 prolonged outdoor training is less feasible), transforming the hot season into a golden window for building a strength foundation. 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 aligns perfectly with periodized strength training, becoming a strategic advantage for local athletes.

Debunking Common Myths

Regarding research on the time course of mTORC1 activation following a single heavy resistance training session, many claims circulating outside academia contradict the scientific evidence. The following clarifies each one.

Myth 1: “Lifting weights will make you bulky and heavy, dragging down your endurance.” Evidence shows that maximal-strength-oriented training (high intensity, low volume) primarily induces 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 true. High-repetition, light-load training provides insufficient stimulus for neural drive and tendon stiffness, and numerous studies indicate that heavy-load, low-repetition training yields 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 require 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, research on the time course of mTORC1 activation following a single heavy resistance training session 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, multi-layered 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 molecular-level interval 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 progress with objective metrics throughout, so that strength truly translates into speed and endurance on the course. Science has already pointed the way—what remains is putting it into practice with every squat down and stand up.

Related Reading

• Strength Maintenance in Older Athletes: Research on the Minimum Effective Dose of Resistance Training Frequency
• Specific Benefits of Resistance Training on Bone Density: A Site-Specific Longitudinal Study
• Differences in Effectiveness Between Bodyweight and Machine Training: Functional Transfer of Open Chain vs. Closed Chain
• Aerobic Training Conversion of Fast-Twitch Muscle Fibers: Research on Muscle Fiber Type Transition in Long-Duration Endurance Training