Analysis Metrics Guide

Lateral Movement Standard Deviation

Lateral Deviation

Purpose:

Evaluate the degree of 'wobbling' or 'instability' of knee joints in lateral movement throughout the entire pedaling process.

Calculation:

The program extracts the core 60% data points from the pedaling trajectory, calculates the average position of these points on the horizontal (x-axis), then uses statistical formulas to calculate the overall deviation of all points from this average position.

Interpretation:

The smaller the value, the less left-right wobbling of the knee, the more stable the trajectory; the larger the value, the more unnecessary left-right wobbling exists, wasting energy on lateral movement.

One-sentence summary:

This metric looks at the 'thickness' of the trajectory. An ideal trajectory should be 'thin and tall'.

Core Stroke Separation

Path Separation

Purpose:

Evaluate whether the downstroke (power) and upstroke (recovery) phases overlap horizontally.

Calculation:

The program calculates the horizontal average positions of the core 60% 'downstroke' and 'upstroke' trajectories separately, then takes the absolute value of the difference between these two average positions.

Interpretation:

Ideally, this value should be close to 0, indicating that the up and down strokes are basically on the same vertical line. If the value is large, it indicates an '0' or '8' shaped trajectory, usually related to improper saddle height.

One-sentence summary:

This metric looks at whether the trajectory 'overlaps'. Ideally, the up and down stroke paths should highly overlap.

Top-Bottom Horizontal Displacement

Lateral Shift at Extremes

Purpose:

Evaluate the overall 'tilt' angle or 'drift' direction of the knee joint pedaling trajectory.

Calculation:

The program traverses the complete trajectory data, finds the highest point (TDC) and lowest point (BDC) in the path, then subtracts the x-coordinate of the highest point from the x-coordinate of the lowest point.

Interpretation:

This value directly reflects whether the knee has an overall tendency to 'swing out' or 'tuck in'. If the value significantly deviates from 0, it indicates the entire trajectory is tilted, usually a clear signal of improper saddle height or cleat position.

One-sentence summary:

This metric looks at the 'skewness' of the trajectory. An ideal trajectory should be 'straight'.

Knee Joint Angle (at BDC)

Knee Joint Angle at Bottom Dead Center

Purpose:

Assess the degree of knee extension at the lowest pedaling point, which directly affects pedaling efficiency and knee health.

Calculation:

When the program detects the lowest point of the pedaling trajectory (BDC, Bottom Dead Center), it calculates the angle between the femur and tibia. Specifically, it uses the spatial positions of the hip, knee, and ankle joints to derive the angle using vector angle formulas.

Interpretation:

Ideal ranges vary by cycling type: road bike competitive mode ~25-35°, leisure mode ~30-40°; mountain bike ~30-40°; triathlon bike ~20-30°. Angles too small (<25°) may cause knee pain and hip closure; angles too large (>40°) indicate saddle too low, reducing pedaling efficiency.

One-sentence summary:

This angle is like the compression of a spring—too tight will damage it, too loose will be powerless.

Hip Joint Angle (at BDC)

Hip Joint Angle at Bottom Dead Center

Purpose:

Assess the rider's torso lean and hip opening during the power phase, affecting power output and aerodynamics.

Calculation:

At the lowest pedaling point, calculate the angle between the torso (line from shoulder to hip joint) and the thigh (line from hip to knee joint).

Interpretation:

Ideal ranges: road bike competitive ~40-50°, leisure ~50-65°; mountain bike ~45-60°; triathlon bike ~35-45°. Angles too small trigger 'hip closure' effect, limiting power output and breathing; angles too large lose aerodynamic advantage.

One-sentence summary:

This angle determines your 'folding' degree—fold too tight and you'll struggle to breathe, too loose and you face high wind resistance.

Elbow Joint Angle

Elbow Joint Angle

Purpose:

Assess arm bend degree, affecting upper body comfort, vibration absorption capacity, and overall aerodynamic posture.

Calculation:

Calculate the angle between the upper arm (shoulder to elbow joint) and forearm (elbow to wrist joint), taking the average over the entire pedaling cycle.

Interpretation:

Ideal ranges: road bike competitive ~90-110°, leisure ~100-120°; mountain bike ~90-120° (needs more bend for shock absorption); triathlon bike ~70-90° (leaning on TT bars). Angles too small cause arm fatigue and shoulder/neck tension; angles too large lose cushioning ability.

One-sentence summary:

The elbow is like a shock absorber—moderate bending absorbs road vibrations while maintaining control.

Back Angle

Back Angle

Purpose:

Assess the torso's tilt angle relative to the horizontal plane, the most critical balance point between aerodynamics and comfort.

Calculation:

Calculate the angle between the torso (line from shoulder to hip joint) and the horizontal plane, taking the average over the entire pedaling cycle. Smaller angles indicate more horizontal position, larger angles indicate more upright.

Interpretation:

Ideal ranges: road bike competitive ~25-35°, leisure ~35-50°; mountain bike ~30-45°; triathlon bike ~10-25° (ultimate aero). Angles too small require extremely strong core strength and may affect breathing; angles too large significantly increase wind resistance.

One-sentence summary:

Back angle is like an airplane's dive angle—flatter is faster, but requires a stronger 'engine' (core strength) to support.