Explosive Power Output and the ATP-PCr System: A Study of Energy Systems in Sprint Training

Power Output Capacity and the ATP-PCr System: Energy System Research on Short Sprint Training

In the landscape of contemporary sports science, “power output capacity and the ATP-PCr system” stands as one of the core topics spanning strength and conditioning, exercise physiology, and biomechanics. For a long time, a deeply entrenched 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 question with rigorous randomized controlled trials (RCTs), muscle biopsies, electromyography (EMG), ultrasound elastography, and molecular biology tools, the conclusions were nearly unanimous: appropriately designed power output capacity and ATP-PCr system training not only fails to impair endurance performance but can, through multiple pathways—including the relative composition of fast-twitch and slow-twitch muscle fibers, cross-sectional area, and recruitment order—improve exercise economy, delay fatigue, and enhance terminal sprint capacity.

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

For athletes seeking improvement, understanding the science behind “energy system research on short sprint training” means being able to break free from the rut of blindly imitating elite training plans and to build 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 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: Grgic et al. (2019)

Published in the Journal of Science and Medicine in Sport, this study (Resistance training frequency and skeletal muscle hypertrophy: a review) employed a systematic review and meta-analysis, involving 18 female road cyclists with a 16-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while assessing 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 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 1.2, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven 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: Folland et al. (2007)

Published in Sports Medicine, this study (The adaptations to strength training: morphological and neurological contributions to increased strength) employed a cross-sectional correlational analysis, involving 16 national-level endurance athletes with a 6-month intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while assessing 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 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 1.2, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven 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: Behm et al. (1993)

Published in Sports Medicine, this study (Velocity specificity of resistance training) employed a longitudinal tracking design, involving 16 national-level endurance athletes with a 10-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while assessing 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 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 0.51, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven 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: 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 crossover design, involving 30 marathon runners with a 10-week intervention period. Before and after the intervention, researchers measured maximal strength (1RM or isokinetic peak torque), exercise economy, maximal oxygen uptake (VO₂max), and time-trial performance, while assessing 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 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 1.18, reaching both statistical and practical significance. Notably, this improvement was not accompanied by significant weight gain, nor was any decline in VO₂max observed—directly refuting the popular claim that “strength training makes you heavier and slower.” The researchers primarily attributed the benefits to improved unit output efficiency driven 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 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 crossover design with 20 amateur cyclists over a 10-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 used muscle biopsies or imaging tools to assess changes in the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers.

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 the primary performance measures, with an effect size (Cohen’s d) of 0.45, reaching statistical and practical significance. Notably, this improvement was not accompanied by significant body weight gain, 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 improved output efficiency per unit resulting from the relative composition, cross-sectional area, and recruitment order of fast-twitch and slow-twitch muscle fibers, rather than mere muscle mass accumulation.

Taken together, the five studies above point to a clear consensus: under well-controlled conditions, power output capacity and the ATP-PCr system exert positive and reproducible effects 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
Grgic	2019	Systematic review and meta-analysis	25 weeks	+5.8%	0.47
Folland	2007	Longitudinal tracking study	16 weeks	+3.5%	0.97
Behm	1993	Cross-sectional correlational analysis	10 weeks	+4.2%	0.82
Schoenfeld	2010	Systematic review and meta-analysis	16 weeks	+8.3%	0.42
Aagaard	2010	Double-blind intervention study	10 weeks	+3.5%	0.58

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 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 power output capacity and the ATP-PCr system 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 in the muscle itself. During the first 4 to 6 weeks of training, rapid strength gains primarily stem from increased motor unit recruitment rates, higher discharge 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 generate higher rates of force development (RFD) at the same muscle cross-sectional area—critical 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 exert their effects. Particularly crucial for endurance athletes is the “subtype shift” in muscle fiber types—the most fatigable IIx fibers tend to convert toward the more fatigue-resistant IIa type while retaining considerable contraction speed. This means muscles become 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 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 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 impacts on endurance performance:

Mechanism Level	Primary Changes	Typical Timeline	Impact on Endurance Performance
Neural adaptation	Motor unit recruitment↑, discharge frequency↑, 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	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 temporal relay: neural adaptations provide the “immediate” strength gains first, followed by structural remodeling of muscle and tendon that delivers “sustained” efficiency dividends. Understanding this timeline helps athletes remain patient during the early training phase when they may appear to be “just getting stronger, not bigger,” and avoid giving up before the long-term dividends are reaped.

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 for explosive power and the ATP-PCr system are not a linear “more is better” relationship, but rather there is a minimum effective dose and an inflection 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 accompanying weight gain) to a minimum. Research by Folland 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 period, in-season	Small	Low
Standard Effective Dose	2× per week, 3–4 sets per movement	Base period, build period	Medium–Large	Medium
High Dose	3× per week, 4–6 sets per movement	Off-season strength-specific period	Large (but diminishing returns)	High (interference risk ↑)

Individual differences play an important role here. Genetic polymorphisms (such as ACTN3, muscle fiber type distribution), training history, 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 individualized and continuously monitored with objective indicators (such as 1RM progress, 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 itself, but by the degree to which it competes with endurance training for recovery resources. This is also why elite endurance athletes’ strength training doses are typically much more conservative than those of pure strength athletes—they pursue “sufficient” strength stimulus, not “maximal” strength stimulus.

Differences Across Populations

The benefits of explosive power and the ATP-PCr system 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 foundation, 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 decide victory or defeat in competition.

Sex Differences. Vikmoen et al.'s research on female road cyclists is particularly important because early literature was predominantly male-based. 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 sexes mainly 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) 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 Focus
Beginners	Neural adaptation dominant, rapid progress	Establish movement quality, progressive loading
Advanced Athletes	Adaptation slows, requires refined stimuli	Periodization, power/eccentric orientation
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 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 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 movements to perform, what intensity to use, when to schedule them, and how to monitor.

Movement 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 explosive power and the ATP-PCr system, corresponding accessory movements (such as eccentric components, plyometric jumps, or core stability training) can be added.

Intensity and Sets. When maximal strength is the primary goal, a 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) combined with “maximal intended velocity” execution—movement speed itself is the stimulus. The table below shows a sample off-season weekly program:

Day	Main Training	Strength Program Example
Monday	Endurance (long slow distance)	—
Tuesday	Strength (maximal strength orientation)	Squat 5×5, Romanian deadlift 4×6, calf raise 3×8
Wednesday	Endurance (tempo/threshold)	—
Thursday	Strength (power orientation)	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, 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 “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 continuously declines 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 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 power output capacity and the ATP-PCr system.

Recovery management in hot, humid conditions. Taiwan’s summer heat and humidity can hinder recovery from 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 races. Classic Taiwanese events such as Wuling (West Approach), the North 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 muscular strength required to “sustain 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, which involves elevation changes of up to 3,000 meters, maximal strength reserves in the lower limbs allow riders to maintain pedaling margin on the latter steep sections, avoiding the predicament of “legs giving out first.”

Local training resources and seasonal rhythm. Gyms are widely accessible in most Taiwanese cities and counties, allowing cyclists to utilize the free weights area for squats and deadlifts. Those training at home can achieve similar stimuli using 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 prolonged outdoor training is impractical), transforming the hot season into a golden window for building a strength foundation. Then, when autumn and winter bring cooler weather, return outdoors to convert that strength into actual riding performance. In this way, Taiwan’s unique seasonal rhythm can be perfectly integrated with periodized strength training, becoming a strategic advantage for local athletes.

Common Myth-Busting

Regarding power output capacity and the ATP-PCr system, many claims circulating among enthusiasts contradict 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 induces neural and tendon adaptations, with limited increases in muscle cross-sectional area. Most studies show no significant change in body weight, while performance actually improves due to enhanced efficiency.

Myth 2: “Endurance athletes should only do high-repetition, light-weight ‘muscular endurance’ training.” The opposite is 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 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, power output capacity and the ATP-PCr system are 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 jointly support one conclusion: appropriate resistance training is an indispensable component of the endurance athlete’s toolbox.

Future research directions include using genetic and molecular markers to predict individual responses, 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 pragmatic 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 road. Science has already pointed the way; what remains is putting it into practice with every squat down and stand up.

Related Reading

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• Strength Maintenance in Older Athletes: Research on the Minimum Effective Dose of Resistance Training Frequency
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