Pedaling Efficiency Index (Gross Efficiency) Linked to Carbohydrate Burn Rate: A Quantitative Model of How High-Efficiency Pedaling Saves Muscle Glycogen

1. Introduction and Cutting-Edge Research Background

In the world of professional cycling and triathlon, “Pedaling Efficiency” has always been the holy grail pursued by sports scientists and coaching staff. Traditional training philosophy often focuses on improving maximal oxygen uptake (VO₂max) and Functional Threshold Power (FTP). However, in recent years, the international sports science community has gradually shifted its research focus toward “Metabolic Economy” and “Gross Efficiency” (GE). The reason is straightforward: in long, high-intensity races, the key to victory is often not how many watts you can produce, but rather the “fuel cost” required to sustain that wattage.

Gross Efficiency (GE) is defined as the ratio of mechanical power output to total human energy expenditure, expressed as a percentage. Its mathematical formula is: GE = (Mechanical Power / Metabolic Power) × 100%. Under laboratory conditions, oxygen consumption (VO₂) and carbon dioxide production (VCO₂) are measured using gas analyzers (such as the ParvoMedics TrueOne 2400 or Cortex Metalyzer 3B), allowing calculation of the Respiratory Exchange Ratio (RER), which in turn enables estimation of the oxidation ratios of carbohydrates and fats, yielding precise metabolic power.

The most representative modern research comes from the exercise physiology team at Maastricht University in the Netherlands. Their studies indicate that GE values for long-term trained professional cyclists typically fall between 21% and 24%, while amateur riders generally range between 18% and 20%. This seemingly small difference of just 3 to 4 percentage points can, over prolonged high-intensity riding, result in a difference of several hundred grams of muscle glycogen consumption, directly impacting pacing ability and breakaway power in the latter stages of a race.

Importantly, GE is not an innate physiological trait. In recent years, multiple meta-analyses have confirmed that through specific pedaling technique training, strength training, and bike fit adjustments, GE can be significantly improved by 1.5 to 2.5 percentage points within 8 to 12 weeks. This means GE improvement is one of the few physiological metrics that simultaneously offers both “significant performance gains” and “high trainability.” This article will comprehensively analyze the interrelationship between GE and carbohydrate burning rate from four perspectives—biochemical metabolic pathways, biomechanical models, comparative analysis of measured data, and periodized training plans—and construct a practical quantitative model for muscle glycogen sparing.

2. Core Mechanisms of Exercise Physiology and Biomechanics

2.1 Biochemical Pathways of Energy Metabolism and the Molecular Basis of GE

Human energy supply during cycling relies primarily on three systems: the Phosphocreatine System, the Glycolytic System, and Oxidative Phosphorylation. During sustained power output exceeding 2 minutes, the oxidative phosphorylation system supplies over 95% of adenosine triphosphate (ATP) demand. At this point, carbohydrates (in the form of muscle glycogen and blood glucose) and fats (in the form of free fatty acids) are oxidized through different biochemical pathways to produce ATP.

The complete oxidation of carbohydrates follows this overall reaction: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + approximately 32 ATP. Each gram of carbohydrate completely oxidized yields approximately 4.1 kilocalories (kcal) of energy, but the human body’s actual mechanical energy conversion rate is only about 20% to 24%. The remaining energy is dissipated as heat. Fat oxidation produces approximately 9.3 kcal/g, but because fat oxidation requires a greater amount of oxygen participation, its ATP production efficiency per unit of oxygen is lower than that of carbohydrates. This explains why, during high-intensity exercise, the human body preferentially selects carbohydrates as the primary fuel—because per unit of time, carbohydrate oxidation can provide a higher ATP turnover rate.

2.2 Biomechanical Model: The Mechanical Roots of Pedaling Efficiency

From a biomechanical perspective, individual differences in GE stem from mechanical factors at multiple levels. The first is the “Effective Force” ratio of pedaling technique. Within the 360 degrees of one crank revolution, only a specific angular range around the Bottom Dead Center (BDC) can produce positive torque. Elite riders can maintain high tangential force output during the 0 to 180-degree (downstroke phase) while simultaneously reducing “Negative Torque” generation through active lifting of the contralateral leg during the 180 to 360-degree (upstroke phase).

The mathematical model of force distribution can be expressed as: Torque output T(θ) = F_t(θ) × L, where F_t(θ) is the force in the tangential direction of the crank and L is crank length. The Pedaling Effectiveness Index (PEI) is defined as the ratio of positive work to total work: PEI = W_positive / (W_positive + |W_negative|). Research shows that amateur riders have a PEI of approximately 0.75 to 0.80, while professional riders can reach 0.85 to 0.90. This difference directly affects GE—because the generation of negative torque means the agonist muscles must perform additional work to overcome the resistance of the contralateral leg, resulting in unnecessary energy waste.

2.3 The Mathematical Link Between GE and Carbohydrate Burning Rate

The quantitative relationship between GE and fuel selection can be established through the following derivation. Assume a rider sustains a mechanical power output of 200W for 5 hours. Total mechanical work is: W_total = 200W × 18,000 seconds = 3,600,000 joules = 860 kcal.

When GE = 20%, the total metabolic energy required is: E_metabolic = 860 / 0.20 = 4,300 kcal. If the RER at this intensity is 0.90 (representing approximately 66.7% energy contribution from carbohydrates), then carbohydrate oxidation = 4,300 × 0.667 / 4.1 ≈ 700 grams.

When GE increases to 21%, the total metabolic energy required drops to: E_metabolic = 860 / 0.21 = 4,095 kcal. Under the same RER conditions, carbohydrate oxidation = 4,095 × 0.667 / 4.1 ≈ 666 grams.

The difference between the two is approximately 34 grams. If this difference is extrapolated to longer race durations (such as the 6 to 8 hours of the Wuling Challenge, or the 180-kilometer bike leg of KONA, lasting approximately 4.5 to 5 hours), and considering that increased intensity in the latter stages raises RER above 0.95, a 1% improvement in GE will easily save over 150 grams of muscle glycogen. This is the core argumentative foundation of the quantitative model presented in this article.

3. Key Parameter Measurements and Comparative Analysis

3.1 Laboratory Gas Analysis Measured Data

The following data is compiled from a study involving 20 subjects (10 amateur riders, 10 professional riders) who underwent a Ramp Test and Submaximal Steady-State Test. Test conditions: room temperature 20°C, humidity 50%, using each rider’s personal race bike equipped with a power meter (SRM or Power2Max), cadence maintained at 90±2 rpm.

3.2 Fuel Consumption Simulation for a 5-Hour 200W Ride at Different GE Levels

This simulation assumes RER remains at 0.90 (carbohydrate contribution 66.7%) and riding intensity remains at a steady 200W output. If we consider a real-world scenario where intensity increases to 230W in the latter stages with RER rising to 0.95, the muscle glycogen saved by improving GE from 20% to 21% would expand from 36 grams to over 80 grams; if improving from 19% to 22%, total savings could reach 150 to 180 grams—this is precisely the critical difference determining whether a rider “bonks” in the final 30 kilometers of a race.

4. Periodized Training Plan and Pedaling Technique Adjustment Guide

4.1 Phase 1: Technical Foundation Period (Weeks 1-4)

The goal of this phase is to establish neuromuscular connections for efficient pedaling. Schedule 2 dedicated pedaling technique sessions per week, each lasting 45 to 60 minutes.

• One-Leg Drills: On a trainer, pedal with a single leg for 5 minutes per leg, power maintained at 50 to 60% FTP, cadence 90 to 100 rpm. The focus is on eliminating the “dead zones” at Top Dead Center (TDC) and Bottom Dead Center (BDC) to make force output more uniform.
• Cadence Spin-ups: Progressively accelerate from 90 rpm to 120 rpm, hold for 30 seconds, then recover. Repeat 8 to 10 sets. This training aims to enhance the nervous system’s control over rapid muscle contractions.
• Isometric Force Maintenance Training: With the crank in the horizontal position (3 o’clock direction), apply static pedaling pressure, holding for 10 to 15 seconds, repeating 6 to 8 times per leg. This exercise strengthens force transmission efficiency during the “downstroke propulsion” phase of pedaling.

4.2 Phase 2: Strength Integration Period (Weeks 5-8)

This phase translates foundational strength into pedaling power. Schedule 2 weight training sessions and 2 hill interval sessions per week.

• Weight Training Plan: Back Squat 3 sets × 5 reps (85% 1RM), Single-leg Romanian Deadlift (RDL) 3 sets × 8 reps, Standing Calf Raise 3 sets × 15 reps. Allow at least 48 hours between weight training and high-intensity cycling sessions.
• Hill Interval Training: Choose a 6 to 8% gradient climb (such as the Pingdengli section of Yangmingshan’s Fengzhongjian route), perform 3 to 5-minute climbing repeats at 90 to 105% FTP, recover with easy riding on the descent, repeat 4 to 6 times. This training simultaneously improves muscular force output efficiency and aerobic metabolic capacity.

4.3 Phase 3: Metabolic Economy Conversion Period (Weeks 9-12)

The goal of this phase is to translate improved strength and technique into actual GE gains. Schedule 1 gas analyzer test per week to track GE improvement progress.

• Sweet Spot Long Ride: Once per week, total duration 2.5 to 3.5 hours, power maintained at 85 to 92% FTP. This intensity zone (boundary between Zone 3 and Zone 4) is most effective at stimulating mitochondrial density increases and muscle glycogen-sparing adaptations.
• Tempo Ride with RPE Monitoring: Ride at 75 to 80% FTP for 90 minutes, recording Rating of Perceived Exertion (RPE) and heart rate every 10 minutes. The goal is to maintain power output without decline at the same RPE in later stages.
• Low Cadence Overgear Training: On flat terrain, ride at 60 to 70 rpm and 85 to 90% FTP for 20 minutes, repeating 2 sets. This training strengthens tension adaptation of slow-twitch muscle fibers (Type I), improving force transmission efficiency.

4.4 Pre-Race Tapering and GE Maintenance

Begin progressive tapering 7 to 10 days before race day, reducing training volume to 60%, 40%, and 30% of normal levels, while maintaining 1 to 2 short (20 to 30-minute) high-cadence activation sessions (100 to 110 rpm) to keep neuromuscular pathways active. Two days before the race, perform a 30-minute easy ride with 2 to 3 sets of 15-second sprints to maintain muscular explosive power memory.

5. Race Nutrition, Environmental Adaptation, and Race-Day Strategies

5.1 Quantitative Carbohydrate Supplementation Strategy

Based on the interrelationship between GE and carbohydrate burning rate, race nutrition should adopt a “dynamic adjustment” approach rather than fixed dosages. For a rider with GE=21% at 200W output, the carbohydrate oxidation rate is approximately 60 to 70 grams per hour. To delay muscle glycogen depletion, 60 to 90 grams of carbohydrates should be supplemented per hour (with a 1:0.8 glucose-to-fructose ratio being optimal, as the two utilize different intestinal transport channels, potentially increasing total absorption rate to 90 to 105 grams per hour).

Specific supplementation schedule recommendation: Consume 150 to 225 ml of sports drink (containing 6 to 8% carbohydrates) every 15 minutes, paired with 1 energy gel (approximately 25 grams of carbohydrates) or half an energy bar every 45 minutes. In the latter stages of a race (final 90 minutes), if intensity increases, carbohydrate intake should be raised to 90 to 100 grams per hour, prioritizing liquid nutrition to accelerate gastric emptying.

5.2 Hydration and Electrolyte Balance

Fluid intake should be between 500 and 750 ml per hour, adjusted based on temperature and sweat rate. Electrolyte supplementation should focus primarily on sodium (500 to 700 mg per hour), with potassium and magnesium as secondary. This can be achieved through sodium salt tablets or the electrolyte content in sports drinks. When dehydration reaches 2% of body weight, GE may decline by 3 to 5%, because hemoconcentration leads to decreased cardiac output, reduced muscle blood flow, and consequent deterioration of metabolic efficiency.

5.3 Environmental Adaptation Strategies

• Hot Environments (e.g., KONA’s hot weather): Undergo heat acclimation 7 to 10 days before the race (30 to 60 minutes daily of low-intensity riding in environments above 30°C) to increase plasma volume and sweating efficiency. During the race, a “Pre-cooling” strategy can be employed—consume a slushie or apply ice packs to the neck and thighs 20 minutes before the start to lower core temperature by 0.3 to 0.5°C, helping maintain GE stability in the latter stages.
• High-Altitude Environments (e.g., Wuling’s 2,275 meters): Arrive at Cingjing or Wushe 3 to 5 days before the race for acclimatization. For every 1,000 meters of altitude gain, VO₂max decreases by approximately 6 to 8%, but GE itself is not directly affected by altitude—the key is adjusting pacing based on the reduced VO₂max reserve to avoid pushing intensity too early and causing excessive carbohydrate depletion.
• Low Temperatures and Wind/Rain (e.g., North Coast spring races): Low temperatures increase skeletal muscle shivering thermogenesis, a process that consumes additional carbohydrates. It is recommended to wear windproof/waterproof outerwear to maintain core temperature and increase the carbohydrate proportion in nutrition by 10% to compensate for the extra expenditure.

5.4 Race-Day Pacing Strategy

Using the One-Day Taipei to Kaohsiung (approximately 360 km) or the Twin Towers (520 km) as examples, the entire ride should be primarily “power-paced” with heart rate as a secondary reference. Maintain 65 to 70% FTP for the first third; increase to 72 to 78% FTP for the middle third; in the final third, if perceived exertion allows, increase to 80 to 85% FTP. The key is maintaining stable GE throughout—if heart rate rises more than 5% at the same power output, or RPE increases noticeably, immediately reduce power by 5 to 8% to return the body to its metabolic comfort zone.

6. Common Operational Mistakes and Scientific Myth-Busting

Myth 1: “The Heavier and Harder You Push the Pedals, the Better the Training Effect”

Many riders believe that pushing harder gears provides better strength training, but in reality, excessively low cadence (below 70 rpm) increases the unit tension on muscles, causing premature recruitment of Type II (fast-twitch) muscle fibers. Fast-twitch fibers consume carbohydrates at 3 to 4 times the rate of slow-twitch fibers and are prone to localized fatigue. Scientific research recommends maintaining a cadence of 80 to 100 rpm for general training, which is the range most consistent with human neuromuscular economy.

Myth 2: “GE Is Determined at Birth and Training Has Limited Effect”

This myth has been refuted by multiple long-term longitudinal studies. A 20-week intervention study showed that after performing pedaling technique training 3 times per week for 45 minutes per session, subjects’ GE improved by an average of 2.1 percentage points. The key is that training must incorporate “Deliberate Practice” elements—focusing on movement quality rather than merely pursuing training volume.

Myth 3: “As Long as FTP Is High Enough, GE Doesn’t Matter”

FTP represents “how much power you can produce,” while GE represents “how much fuel it costs to produce that power.” In short-distance events (such as a 10 km time trial), FTP indeed has a greater impact than GE; however, in races exceeding 3 hours, the importance of GE gradually surpasses FTP. This is because muscle glycogen stores are limited (approximately 500 to 600 grams). At GE=20%, a 200W output consumes approximately 92 grams of carbohydrates per hour, depleting all reserves within 5 hours; whereas a rider with GE=23% consumes only about 70 grams per hour, retaining approximately 150 grams of reserve after 5 hours.

Myth 4: “The More Nutrition You Consume, the Better—It Can Completely Offset the Disadvantage of Low GE”

Although consuming carbohydrates during a race can delay muscle glycogen depletion, the human intestinal absorption rate has an upper limit (approximately 90 to 105 grams per hour). Intake exceeding this limit will only accumulate in the gut, causing stomach discomfort, nausea, or even vomiting, which actually reduces riding efficiency. Therefore, nutrition strategies should be viewed as a “supplement” to GE rather than a “substitute.” Improving GE is the fundamental solution.

7. Expert FAQ

Q1: How Do I Measure My GE Value?

Measuring GE requires synchronized use of a gas analyzer and a power meter. In a laboratory setting, you will ride on a power meter-equipped trainer at several different intensities (e.g., 100W, 150W, 200W, 250W) for 6 minutes each at steady state, while wearing a mask to collect expired air. The analyzer calculates per-minute VO₂ and VCO₂, and metabolic power is calculated using the Weir Equation: Metabolic Power (kcal/min) = 3.941 × VO₂(L/min) + 1.106 × VCO₂(L/min). GE is then mechanical power divided by metabolic power. If you cannot access a laboratory, a high-precision power meter combined with heart rate variability (HRV) and RPE can provide rough estimates, though with lower accuracy. It is recommended to test once before the season and once mid-season to track training effectiveness.

Q2: Will Increasing Cadence Always Improve GE?

Not necessarily. The effect of cadence on GE follows an inverted U-shaped curve—too low (<70 rpm) increases muscular tension costs, while too high (>110 rpm) increases cardiorespiratory metabolic costs and neuromuscular fatigue. Most studies show that the optimal cadence for GE falls between 85 and 95 rpm, though individual differences exist. It is recommended to perform a “Cadence Ladder Test”: at the same power output (e.g., 150W), ride sequentially at 70, 80, 90, 100, and 110 rpm for 4 minutes each, measuring RPE and heart rate to identify your personal most economical cadence range.

Q3: How Long Does It Take for GE Improvements to Reflect in Race Performance?

Generally, 6 to 8 weeks of dedicated training can yield a 1 to 1.5 percentage point improvement in GE, which translates to approximately 60 to 100 grams of carbohydrate savings in races lasting over 3 hours. When combined with strength training and body weight management, an improvement of over 2 percentage points can be expected within 8 to 12 weeks. It should be noted that GE improvement is not linear—early progress is faster, while later stages tend to plateau. It is recommended to undergo laboratory testing every 4 to 6 weeks to confirm progress and adjust training stimuli.

Q4: Is Female Riders’ GE Different from Male Riders’?

Research shows that when body weight and training volume are controlled, there is no significant difference in GE between female and male riders. However, women’s muscle glycogen storage capacity and carbohydrate oxidation rates are slightly lower than men’s. Therefore, at the same GE, female riders may face muscle glycogen depletion risk earlier in ultra-endurance events. It is recommended that female riders maintain carbohydrate intake of 70 to 85 grams per hour during races, and pay particular attention to the effects of the menstrual cycle on metabolism—basal metabolic rate is higher during the Luteal Phase, potentially requiring an additional 5 to 10% increase in carbohydrate intake.

Q5: How Can I “Real-Time” Determine If My GE Is Declining During a Race?

GE cannot be directly measured during a race, but it can be monitored through proxy indicators. The most practical method is the “Power-to-Heart Rate Ratio”: if heart rate rises more than 5% at the same power output compared to the early stages of the race, accompanied by increased RPE, it indicates declining metabolic efficiency. Another indicator is “Pedaling Smoothness”—on a trainer, this can be observed through the real-time torque distribution graph from a power meter. If smoothness decreases, it indicates obvious dead zones in force output. At this point, you should slightly reduce power or change riding position to restore smooth pedaling. Conducting a “GE baseline test” before the race and recording personalized indicators can help you more accurately assess metabolic status during competition.

Key Reference Highlights (for further reading): Hopker et al. (2009) “The effects of training on gross efficiency in cycling”; Moseley & Jeukendrup (2001) “The reliability of cycling efficiency”; Louis et al. (2012) “The effects of cadence on gross efficiency in cycling”; and the GE measurement standards recommendation document from the International Cycling Science Consortium.