AI 速览
- The pedal stroke divides into power (0-180°) and recovery (180-360°), with peak torque around 90-110° past TDC where the femur aligns with the pedal spindle.
- Only the tangential component of pedal force produces work — 30-50% of total force is wasted as radial load even in elite cyclists.
- Index of Effectiveness (tangential divided by total force) sits at 70-85% in pros and 50-65% in recreational riders.
- Cadence redistributes muscle load rather than creating power: too low spikes joint torque, too high burns energy just moving the legs.
/ 01
The Four Phases of the Pedal Stroke
The pedal stroke divides into four functional arcs measured from top dead center (TDC). The power phase (0-180°) produces nearly all positive torque; the recovery phase (180-360°) returns the leg to TDC. Coaches further split these into quadrants: downstroke (0-90°), bottom (90-180°), upstroke (180-270°), and top (270-360°). Each phase has a distinct muscle activation pattern, and each rider blends them differently based on anatomy, fit, and pedaling style.
Peak crank torque lands around 90-110° past TDC — roughly 3 o'clock — where the femur aligns with the pedal spindle and the glute and quad can push straight through it. Mashing at too low a cadence spikes this peak but leaves the rest of the stroke unproductive.
/ 02
Effective Force: Tangential Beats Total
Only the tangential component of pedal force — perpendicular to the crank arm — produces torque at the bottom bracket. Force along the crank (radial) does nothing useful. Instrumented pedal studies using SRM Science and Garmin Rally force-plate data show even elite cyclists waste 30-50% of their total pedal force as radial load. Novices can exceed 70% waste.
This reframes the pull-up-on-the-upstroke myth. The upstroke contributes only 5-15% of total power at submaximal intensities — its real job is lightening the opposing leg's lift and smoothing the torque waveform so the next downstroke starts cleanly. The aim isn't more total force; it's more effective force applied at the right crank angle.
/ 03
Muscle Activation by Phase
Pedal Stroke Phases and Their Primary Movers
| Phase | Crank Angle | Primary Movers |
|---|---|---|
| Downstroke | 0-90° | Glute max, vasti, soleus |
| Bottom / dead spot | 90-180° | Hamstrings, gastrocnemius |
| Recovery | 180-270° | Tibialis anterior, hip flexors |
| Top / pre-load | 270-360° | Iliopsoas, rectus femoris |
/ 04
Cadence and Muscle Activation
Cadence doesn't change total power — it redistributes muscle load per stroke. At 60 rpm, peak crank forces are high and the glutes and quads carry more work per revolution. At 100 rpm, peak forces drop and the stroke gets rounder, but cardiovascular load rises because moving the legs faster costs internal work.
Self-selected cadence for trained cyclists sits around 80-95 rpm on flat roads, close to the gross-efficiency optimum. Too low grinds the knees and spikes patellofemoral joint force. Too high for a given power output just burns energy spinning without producing more watts.
/ 05
Practical Fixes for a Rounder Stroke
Ankle movement matters: a 10-15° heel-drop through the bottom of the stroke keeps the foot driving forward into the dead spot — the classic scrape-mud-off-the-shoe cue. Stiff, locked ankles waste the transition between downstroke and recovery.
Fit changes redistribute load. Saddle setback shifts the hip relative to the bottom bracket, trading quad for glute recruitment. Saddle height changes knee angle at TDC. Cleat fore-aft trades calf load for quad load. Single-leg isolation drills expose dead spots and retrain the upstroke transition better than any bilateral drill.
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