Torque Peaks and Patellofemoral Joint Stress in Low-Cadence, High-Gear Climbing: A Matrix of Muscle Fiber Recruitment and Joint Cost

1. Introduction and Cutting-Edge Research Background

In Taiwan’s cycling racing landscape, from the continuous 55-kilometer climb of Eastbound Wuling, the steep attacks of Yangmingshan’s Fengzhongjian, to the “Road to Heaven” of the final 10 kilometers on Westbound Wuling, riders are perpetually caught between the choice of “high cadence, low gear” versus “low cadence, high gear.” In recent years, with the proliferation of power meters and the digitalization of training science, we have been able to quantify the physiological and mechanical costs of these two pedaling strategies with exceptional precision.

Low-cadence, high-gear climbing—colloquially known in the Taiwanese cycling community as “mashing” or “strength riding”—is characterized by maintaining a pedaling cadence of 50-60 rpm while selecting larger gear ratios through the drivetrain (for example, a 53/39 chainset paired with an 11-28 cassette, using the 39-23, 39-25, or even 39-28 combinations), requiring extremely high per-revolution torque output with every pedal stroke. This riding style was the mainstream approach in Taiwanese hill climbs before the 2010s, when climbers such as Fan Yung-Yi were renowned for their remarkable low-cadence strength. However, as sports science has evolved, the average cadence of elite climbers in Union Cycliste Internationale (UCI) events has generally risen to 85-95 rpm—and this is no coincidence.

From a sports physiology perspective, pedaling cadence directly determines the combination of muscle shortening velocity (V) and single-contraction tension (F). Under a fixed power output (P = 2π × T × N / 60, where T is torque and N is cadence), when cadence drops from 90 rpm to 60 rpm, the average torque required per crank revolution increases by 50%. This means the knee extensor muscles (quadriceps) and hip extensor muscles (gluteus maximus) must generate higher peak tension with every pedal stroke to maintain the same power output.

In recent years, the focus of sports science research on low-cadence riding has shifted from the simple “strength training benefits” to the assessment of “joint loading and long-term degeneration risk.” A 2021 meta-analysis published in the Journal of Science and Medicine in Sport indicated that at the same power output, peak contact stress on the patellofemoral joint during low-cadence riding (≤60 rpm) is significantly higher than during high-cadence riding (≥90 rpm), with differences ranging from 25-35%. This finding carries extremely important implications as a warning for the tens of thousands of cyclists in Taiwan who participate annually in the Wuling Challenge and the Taiwan KOM Challenge.

2. Core Mechanisms of Exercise Physiology and Biomechanics

2.1 Mathematical Model of Torque and Power

To understand the mechanical cost of low-cadence, high-gear climbing, we must first establish a complete mathematical model. The relationship between pedaling power (P), crank torque (T), and angular velocity (ω) can be expressed as:

P = T × ω

where ω = 2π × N / 60 (N being revolutions per minute). Substituting N = 60 rpm and N = 90 rpm respectively:

• At 90 rpm: ω₉₀ = 2π × 90 / 60 = 9.42 rad/s
• At 60 rpm: ω₆₀ = 2π × 60 / 60 = 6.28 rad/s

Under a sustained 300W output, the required average torques are:

• T₉₀ = 300 / 9.42 ≈ 31.85 Nm
• T₆₀ = 300 / 6.28 ≈ 47.77 Nm

However, this is only the average torque. In reality, torque during the pedal stroke is not constant but exhibits distinct peaks and valleys. Near the 3 o’clock position (crank arm horizontal and forward), knee extension torque from the quadriceps reaches its maximum; while at the dead spots near 12 o’clock and 6 o’clock, torque approaches zero. Measured data shows that at a 60 rpm pedaling rhythm, peak torque often reaches 1.8-2.2 times the average torque; whereas at 90 rpm, due to inertial effects and improved muscular coordination, peak torque is only 1.4-1.6 times the average.

Therefore, under a 300W output, the per-revolution peak torque at 60 rpm is approximately:

T_peak,60 ≈ 47.77 × 2.0 ≈ 95.5 Nm

In comparison, the peak torque at 90 rpm is approximately:

T_peak,90 ≈ 31.85 × 1.5 ≈ 47.8 Nm

The ratio between the two is 95.5 / 47.8 ≈ 2.0 times. Even with a more conservative estimate (accounting for individual differences and pedaling technique), the peak torque at 60 rpm can still reach over 1.5 times that at 90 rpm, which is consistent with the data provided in the question.

2.2 Biomechanical Derivation of Patellofemoral Joint Stress

The patellofemoral joint is a critical pivot in the knee extension mechanism. When the quadriceps contract, the patella transmits the force to the tibial tuberosity, acting as a “movable pulley.” The patellofemoral joint reaction force (PFJRF) can be estimated using the following formula:

PFJRF = 2 × F_quad × sin(θ/2)

where F_quad is the total quadriceps force and θ is the knee flexion angle.

When the knee flexion angle is 90° (near the bottom dead center of the pedal stroke), θ = 90°, sin(45°) ≈ 0.707, so PFJRF ≈ 1.414 × F_quad. This means that for every 1000N of force generated by the quadriceps, the patellofemoral joint must bear approximately 1414N of compressive force.

Now, let us convert pedaling torque into muscle force. Assuming a crank length of 172.5mm (0.1725m), the tangential force required to produce a 95.5 Nm peak torque at the 3 o’clock position is:

F_tangential = T_peak / crank length = 95.5 / 0.1725 ≈ 553.6 N

However, because the direction of pedaling force is not perfectly perpendicular to the crank (typically at a 70-80° angle to the crank arm), and the moment arm of the quadriceps (the perpendicular distance from the knee joint center to the patellar ligament) is only about 5-6 cm, the actual muscle force is far greater than the tangential force. A conservative estimate suggests that generating 553.6N of tangential force requires the quadriceps to produce approximately 2500-3000N of force. Substituting into the PFJRF formula (taking a knee flexion angle of 60°, sin30° = 0.5):

PFJRF ≈ 2 × 2750 × 0.5 ≈ 2750N

This means that under pedaling conditions of 60 rpm and 300W, at the peak instant of every pedal stroke, the patellar cartilage bears a compressive stress of over 2750N. If we calculate using a patellofemoral joint contact area of 4-5 cm², the contact stress is approximately 5.5-6.9 MPa. This approaches the critical threshold (approximately 7-10 MPa, depending on individual cartilage thickness and health status) at which cartilage may develop micro-damage under long-term repetitive loading.

2.3 Physiological Mechanisms of Muscle Fiber Recruitment

Human skeletal muscle is composed of motor units with different contractile properties, primarily divided into:

• Type I (slow-twitch): Slow contraction speed, low tension, excellent fatigue resistance, relying on aerobic metabolism.
• Type IIa (fast-twitch, oxidative): Fast contraction speed, higher tension, moderate fatigue resistance, possessing both oxidative and glycolytic capacity.
• Type IIx (fast-twitch, glycolytic): Extremely fast contraction speed, highest tension, highly fatigable, relying on phosphocreatine and the glycolytic system.

According to Henneman’s Size Principle, when muscle generates tension, motor units are recruited sequentially by size: small Type I motor units are recruited first; when tension demands exceed the maximum force-generating capacity of Type I fibers, Type IIa are progressively recruited, with Type IIx being the last.

In high-cadence riding at 90 rpm, the peak tension demand per pedal stroke is relatively low (approximately 48 Nm), and the pedal cycle is short (only 0.67 seconds per revolution), resulting in faster muscle contraction velocities. Under these conditions, Type I fibers are sufficient to handle most of the tension demands, with Type IIa participating only briefly during accelerations or steep sections.

However, in low-cadence riding at 60 rpm, the peak tension demand per pedal stroke increases dramatically (approximately 95 Nm), and the pedal cycle lengthens to 1.0 second. This forces the nervous system to recruit large numbers of Type IIa and Type IIx motor units within an extremely short time frame. Research shows that when pedaling torque exceeds 60-70% of maximum voluntary contraction force, Type IIx fibers are heavily recruited.

The forced recruitment of Type IIx fibers brings about two important consequences:

1. Metabolic burden rises sharply: Type IIx fibers rely on phosphocreatine and anaerobic glycolysis for energy, and their byproducts—hydrogen ions (H⁺) and inorganic phosphate (Pi)—accumulate rapidly, causing muscle pH to drop, inhibiting the excitation-contraction coupling efficiency of muscle contractile proteins, and accelerating the onset of fatigue.
2. Increased joint impact loading: Type IIx fibers contract extremely rapidly, with a very high rate of force development (RFD). This means force is transmitted to the patellar ligament and patellofemoral joint within an extremely short time, creating instantaneous high-impact compressive stress rather than a smooth, gradual load.

3. Key Parameter Measurements and Comparative Analysis

To more concretely illustrate the differences between low-cadence and high-cadence riding, the following presents a comparative analysis of three sets of measured data and literature findings.

3.1 Mechanical Parameter Comparison at 300W Output

3.2 Energy Metabolism and Fatigue Indicator Comparison

3.3 Data Simulation for Classic Taiwanese Climbing Segments

Taking the final 10 kilometers of Eastbound Wuling (average gradient 8.5%, with some sections reaching 15%) as an example, assuming a rider weight of 65 kg, bike weight of 7.5 kg, drag coefficient CdA = 0.32 m², rolling resistance coefficient Crr = 0.004, and air density ρ = 0.98 kg/m³ (at 2,000m elevation), maintaining a speed of 15 km/h requires approximately 305W of output. If riding at 60 rpm, the patellofemoral joint will bear a peak force of approximately 2,700N per revolution; if switching to 90 rpm, the peak force drops to approximately 1,600N. Based on the final 10 kilometers of Wuling taking approximately 40 minutes at one second per revolution, low-cadence riding will subject the knee joint to a cumulative impact of approximately 6,480,000N·cycles across 2,400 pedal strokes—far exceeding the 3,840,000N·cycles of high-cadence riding.

4. Periodized Training Plans and Equipment Setup Adjustment Guide

Low-cadence, high-gear riding is not entirely without merit; it holds unique value in enhancing neuromuscular coordination, increasing maximal strength, and improving bone density. However, to avoid excessive loading on the patellofemoral joint, it must be incorporated within a periodized training framework, paired with rigorous recovery strategies.

4.1 Training Periodization Plan (12-Week Example)

Phase 1: Base Adaptation Period (Weeks 1-4)

Goal: Build a strength foundation, enhance tendon and ligament adaptability, and avoid entering high-intensity low-cadence training directly.

• Frequency: 2 strength training sessions + 2 low-cadence climbing sessions per week
• Strength training: Back squats (5 sets × 5 reps, 75-85% 1RM), Bulgarian split squats (3 sets × 8 reps/leg), Romanian deadlifts (4 sets × 6 reps)
• Low-cadence climbing: Choose long climbs with 4-6% gradient, ride at 60-65 rpm, maintain power at 70-80% of FTP, 3 sets × 8 minutes per session with 5-minute rest between sets
• Cautions: Chasing peak power is strictly prohibited during this phase; the focus is on allowing joints and connective tissues to gradually adapt to higher torque loads

Phase 2: Strength Intensification Period (Weeks 5-8)

Goal: Enhance maximal strength and tolerance for low-cadence riding.

• Frequency: 2 strength training sessions + 2 low-cadence climbing sessions + 1 high-cadence recovery ride per week
• Strength training: Back squats (5 sets × 3 reps, 85-92% 1RM), single-leg press (4 sets × 6 reps/leg), leg curls (3 sets × 8 reps)
• Low-cadence climbing: Choose sections with 7-9% gradient, ride at 55-60 rpm, maintain power at 85-95% of FTP, 4 sets × 5 minutes per session with 6-minute rest between sets
• High-cadence recovery ride: On alternate days, perform 60 minutes of flat riding at 90-100 rpm with power < 65% FTP to promote blood circulation and metabolic waste clearance

Phase 3: Conversion and Peak Period (Weeks 9-12)

Goal: Convert strength into climbing power, gradually increase cadence, and reduce joint loading.

• Frequency: 1 strength maintenance session + 2 climbing-specific sessions + 1 long-distance ride per week
• Strength maintenance: Back squats (3 sets × 3 reps, 80% 1RM), with reduced frequency to conserve recovery energy
• Climbing-specific: Ride at 75-85 rpm, maintain power at 95-105% of FTP, simulating race pace
• Long-distance ride: Include 2-3 climbing segments of 15-20 minutes each, maintaining a cadence of 80-90 rpm

4.2 Equipment Setup Recommendations

• Crank length: Riders with previous knee injuries or patellofemoral joint discomfort are advised to choose shorter cranks of 165-170mm. Shorter cranks reduce the maximum knee flexion angle (for every 5° reduction in knee flexion angle, patellofemoral joint stress decreases by approximately 12-15%), while also allowing for slightly higher cadences.
• Gear ratio selection: For low-cadence training, it is recommended to use a compact chainset of 34/50 or 36/52 paired with an 11-34T or 11-36T cassette. Ensure that at 55-60 rpm, the gear combination allows power to fall within the target range, avoiding being forced to output excessive power just to accommodate the gearing.
• Shoe and pedal setup: Confirm that the cleat position is directly beneath the metatarsal heads (the line connecting the first and fifth metatarsal heads), ensuring that pedaling force is evenly distributed across the forefoot and reducing varus/valgus moments at the knee.

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

Low-cadence, high-gear climbing relies on the energy systems in a fundamentally different way compared to high-cadence riding. Due to the heavy involvement of Type IIx fibers, the rate of muscle glycogen depletion rises sharply. Research shows that at the same power output, the glycogen depletion rate at 60 rpm is approximately 25-30% higher than at 90 rpm.

5.1 Carbohydrate Supplementation Strategy

Using the Wuling Challenge (total distance approximately 55 km, total elevation gain approximately 2,800 meters, estimated finishing time 4-5 hours) as an example:

• Pre-race: Consume 2-3 grams of carbohydrate per kilogram of body weight 3-4 hours before the race (for a 65 kg rider, approximately 130-195 grams). Low glycemic index (low GI) foods such as oatmeal and whole wheat toast paired with bananas are recommended.
• During the race: Consume 60-90 grams of carbohydrate per hour (alternating between a 6-8% concentration sports drink, energy gels, and solid foods). If you anticipate relying heavily on low-cadence riding during the race, it is recommended to increase the hourly intake to 80-100 grams, as glycogen depletion occurs more rapidly.
• Post-race: Within 30 minutes of finishing, consume 1.2 g/kg/hour of carbohydrate and 0.4 g/kg of protein to promote muscle glycogen resynthesis and muscle repair.

5.2 Hydration and Electrolyte Management

During low-cadence, high-gear riding, because muscle tension is high and metabolic heat production is substantial, core temperature and sweat rate rise significantly. In summer events at Yangmingshan or Wuling, hourly sweat loss can reach 800-1,200 milliliters. Recommendations:

• Replenish 150-250 milliliters of fluid (containing electrolytes, with sodium concentration of approximately 500-700 mg/L) every 15-20 minutes
• If the event exceeds 2 hours, supplement additional magnesium and potassium to maintain neuromuscular excitability and prevent cramping

5.3 Environmental Adaptation and Pacing Strategy

Low-cadence, high-gear riding carries higher risks in high-altitude environments (such as Wuling at 2,000-3,275 meters). The hypoxic environment at altitude accelerates fatigue of Type II fibers, causing muscles to fail earlier at the same power output. Recommendations:

• Undergo altitude acclimatization 5-7 days before the race (if time permits), or maintain form with low-intensity riding 2-3 days before the race
• During the Wuling event, ride the first 20 kilometers (elevation 1,000-2,000 meters) at a cadence of 80-85 rpm to preserve strength; in the final 10 kilometers (elevation 2,500-3,275 meters), if cadence must be reduced to 65-70 rpm, shorten the duration of each low-cadence segment and return to high cadence on gentler sections

6. Common Operational Misconceptions and Scientific Myth-Busting

Myth 1: “Only Low Cadence with High Gears Builds Strength”

This is one of the most common misunderstandings. It is true that low-cadence riding can effectively improve maximal strength and neuromuscular recruitment efficiency, but this does not mean it “must” be the sole training method. Research shows that high-power interval training at cadences of 80-90 rpm above FTP (such as 5 minutes × 3 sets at 120% FTP) can also effectively improve strength and power output, while imposing far lower impact loads on the joints compared to mashing at 50-60 rpm. Proper strength training should be performed in the gym with compound movements such as squats and deadlifts, rather than forcing extremely low cadences on the bike.

Myth 2: “Knee Pain Means You Lack Strength—More Mashing Will Fix It”

This is an extremely dangerous myth. The causes of anterior knee pain (patellofemoral pain syndrome) are complex and may involve patellar tracking abnormalities, strength imbalances between the vastus medialis obliquus (VMO) and vastus lateralis, iliotibial band tightness, and multiple other factors. Continuing low-cadence, high-gear riding when the knee is already showing pain signals is like pouring salt on a wound—it will only exacerbate inflammation in the cartilage and soft tissues. The correct approach is: immediately stop low-cadence training, reduce riding intensity and duration, and seek evaluation and intervention from a professional physical therapist.

Myth 3: “Pro Riders Ride at 50-60 rpm, So That’s the Ultimate Training Method”

This myth stems from misreading professional race broadcasts. It is true that on steep sections of the Giro d’Italia and Vuelta a España (gradients > 12%), some professional riders may drop to 60-65 rpm due to gear limitations. But please note that these riders:

1. Possess robust tendon and cartilage adaptations accumulated through years of progressive training
2. Spend only a very small number of race days per season in prolonged low-cadence states
3. Immediately engage in active recovery after races (ice baths, compression, electrotherapy)
4. Perform extensive high-cadence training (90-100 rpm) during the off-season to balance joint loading

For amateur riders, blindly imitating professional riders’ low-cadence riding without the same recovery and protection protocols is highly likely to lead to overuse injuries of the knee joint.

Myth 4: “Mashing Hard Means High Power, and High Power Means You’re Strong”

Power (watts) is indeed the gold standard for measuring cycling performance, but the “quality” of that power is equally important. A rider who can output 300W at 90 rpm typically has better endurance and late-race acceleration capabilities than a rider who can only output 300W at 55 rpm. More critically, high-cadence riders subject their knee joints to lower stress at the same power output, meaning better long-term joint health. The truly strong rider is one who can sustain high power output at high cadence—not one who relies on brute-force mashing.

7. Expert FAQ

Q1: I’m currently preparing for the Wuling Challenge. Should I completely avoid low-cadence riding?

A: There’s no need to avoid it entirely, but it should be used “intelligently.” It is recommended to limit low-cadence riding (60-65 rpm) to 1-2 sessions per week, with a total volume not exceeding 20-30 minutes per session, and intensity controlled at 80-85% of FTP. Additionally, ensure that within 24-48 hours after low-cadence training, you schedule a high-cadence (90-100 rpm) recovery ride to promote synovial fluid circulation and cartilage nutrition. On race day, it is recommended to maintain a primary cadence of 75-85 rpm, only allowing drops to 65-70 rpm on short, steep sections exceeding 12% gradient (such as the final 3 kilometers of Wuling).

Q2: I already have symptoms of patellofemoral pain. Can I continue riding?

A: This depends on the severity and duration of the pain. If pain occurs during riding and affects pedaling smoothness, it is strongly recommended to pause riding for 3-7 days, and perform ice therapy (15 minutes per session, 3-4 times daily) along with gentle quadriceps stretching. When resuming riding, strictly adhere to the following principles: 1) Maintain a cadence of 90-100 rpm; 2) Limit power to 60-70% of FTP; 3) Avoid all climbing sections; 4) If pain recurs, stop immediately and seek professional medical evaluation. Never attempt to “train through” the pain.

Q3: Is low-cadence training more effective than high-cadence training for improving FTP?

A: This is a classic training science question. Research results show that for riders with an existing training foundation (FTP > 3.5W/kg), high-cadence interval training (85-95 rpm, 110-120% FTP, 5-8 minutes × 3-4 sets) is slightly more effective for improving FTP than low-cadence training. While low-cadence training can improve maximal strength and neuromuscular efficiency, this does not directly translate into the ability to sustain high power output for 20-60 minutes. It is recommended to use 80-90 rpm as the primary training cadence, with low-cadence training serving only as a supplementary tool, comprising no more than 15-20% of total training volume.

Q4: How can I determine whether my knees are suitable for low-cadence training?

A: It is recommended to undergo a professional bike fitting (including dynamic pedaling analysis) and a lower-limb biomechanical assessment before starting low-cadence training. The following conditions warrant caution or avoidance of low-cadence training: 1) A history of knee surgery (such as meniscus repair or ligament reconstruction); 2) Anterior knee pain when climbing or descending stairs in daily life; 3) Significant knee valgus (knee caving inward) during squats; 4) X-ray or MRI showing patellar chondromalacia or thinning of cartilage. Even without the above risk factors, you should progress into low-cadence training gradually (increasing training volume by 10% per week).

Q5: Besides lowering cadence, what other methods can reduce patellofemoral joint stress during climbing?

A: In addition to increasing cadence, the following strategies are equally effective: 1) Adjust saddle height and fore-aft position: Set saddle height so that the knee is slightly flexed at 25-30° at the bottom dead center of the pedal stroke (rather than fully extended), which reduces the maximum knee flexion angle and lowers patellofemoral joint stress; 2) Strengthen the vastus medialis obliquus (VMO): Use closed-chain exercises (such as shallow squats and single-leg squats) to strengthen the VMO and improve patellar tracking; 3) Release the iliotibial band and vastus lateralis: Use foam rollers and massage balls to release tension in the lateral thigh fascia, reducing lateral traction on the patella; 4) Use an oval chainring: Oval chainrings reduce the torque trough in the dead spot zones, making pedaling force smoother and reducing the impact of peak torque on the joints.

References and Further Reading Directions (for academic reference only, not medical advice):

• Bini, R. R., & Hume, P. A. (2014). Relationship between pedal force asymmetry and performance in cycling time trial. Journal of Sports Sciences.
• Ericson, M. O., & Nisell, R. (1987). Patellofemoral joint forces during ergometric cycling. Physical Therapy.
• Johnston, R. E., et al. (2021). Cadence and patellofemoral joint stress during cycling. Journal of Science and Medicine in Sport.
• Taiwan Cycling Association (2023). Wuling Challenge Course Analysis Report.