RunningForm uses biomechanics reference ranges derived from peer-reviewed sports science research. This page documents the evidence behind each metric, our measurement methodology, and known limitations. We believe in transparency about what the science supports and where our analysis is approximate.
All biomechanics measurements are computed client-side from 2D video using MediaPipe Pose Landmarker. They are estimates, not lab-grade measurements. Reference ranges are pace-adjusted across three tiers: easy (> 6:00/km), tempo (4:30-6:00/km), and fast (< 4:30/km).
Computed as the total range (max minus min) of hip-to-ankle vertical distance across all analyzed frames, divided by the average shoulder-to-ankle distance. Using hip-minus-ankle cancels vertical camera panning. This total-range method yields higher values than per-stride averages reported by wearables like Garmin.
Lower vertical oscillation is beneficial for running economy, though few studies have manipulated VO as an independent variable.
5-10 cm vertical oscillation promoted proper running form and may mitigate injury risk.
Higher vertical oscillation moderately associated with higher energetic cost (r = 0.35).
Color zones: excellent < 6.8 cm, good 6.8-8.9 cm, fair 9.0-10.9 cm, poor 11.0-13.0 cm.
Computed as the angle from vertical of the line connecting shoulder midpoint to hip midpoint, averaged across all frames with valid pose landmarks. Lean source (ankles vs. waist) is determined by comparing upper-body lean to lower-body lean.
Elite runners maintained ~3° lean across all speeds (12-20 km/h). Recreational runners increased from ~5° to ~7.5°.
Most economical group ran with ~5.9° trunk flexion; least economical at ~2.4°.
Running at ~8° lean increased metabolic cost by 8% vs. upright.
More upright trunk posture correlated with better performance across 97 endurance runners.
Increasing trunk flexion by ~7° reduced knee extension moment by ~7% but increased hip extensor demand.
Computed as the absolute horizontal distance between hip midpoint and the visible-side ankle at ground contact frames, divided by the shoulder-to-ankle body height estimate. Expressed as a percentage.
Overstriding results from foot position relative to COM, creating braking impulse proportional to foot-ahead distance.
Elite marathoners land ~0.30 m ahead of COM. Rearfoot vs. non-rearfoot difference was only 0.03-0.04 m — described as "too small to be meaningful."
Every +5 strides/min cadence increase reduced foot-ahead position by ~5.9%.
"There are no cutoffs at which this distance is determined to be abnormal."
Defines overstriding as horizontal distance between greater trochanter and lateral malleolus at foot contact.
Estimated from stride times detected in the gait cycle analysis. A full gait cycle (same-foot to same-foot) covers 2 steps, so cadence = 120 / average_stride_time_seconds. Accuracy depends on detecting at least 2 clean gait cycles.
Increasing step rate 5–10% above preferred reduced energy absorption at the hip and knee, decreased braking impulse, and reduced center-of-mass vertical excursion — without changing speed. A low-barrier, evidence-backed intervention.
Cadence below 160 spm was associated with overstriding patterns across injured runners. Higher cadence correlated with reduced peak hip adduction.
Elite marathoners averaged 180–185 spm across both sexes at race pace.
Ground contact time is measured as the duration from initial foot contact to toe-off for the visible side. Duty factor is computed as GCT divided by the full stride time (derived from cadence), giving the fraction of each stride spent on the ground. Both are reported together.
40 well-trained runners split into high and low duty factor groups showed no significant difference in energy cost. Multiple biomechanical strategies can be equally efficient at endurance speeds.
Faster runners apply greater ground support forces in shorter contact times — speed improvement comes from force production, not simply reducing GCT or increasing leg turnover.
Recreational runners at easy pace average 240–300 ms GCT; trained distance runners 200–260 ms at tempo pace.
Computed from ground contact time estimates for left and right foot strikes detected via gait cycle analysis. Expressed as the percentage difference between sides.
Healthy injury-free runners (n=250) show < 4% spatiotemporal asymmetry across all age groups.
~3.7% increase in metabolic cost for every 1% increase in GCT imbalance (R-squared > 0.65).
Prospective study of 836 recreational runners: asymmetry was NOT associated with higher injury risk. Greater flight time asymmetry was associated with lower injury risk.
"Good" balance = 49.3-50.7% (~1.4% asymmetry).
Many running coaches suggest shortening or lengthening stride length as a coaching cue. RunningForm deliberately does not prescribe a target stride length, and the science is clear on why.
Cavanagh & Williams (1982) showed that trained runners self-select a stride length that is at or very near their individual metabolic optimum — the point where oxygen uptake is minimized for their speed. Deviating from preferred stride length in either direction (too short or too long) increased VO₂ by an average of 2.6–3.4 ml/kg/min. The body finds its own optimum through training adaptation.
What we do flag is overstriding — when the foot lands significantly ahead of the centre of mass, creating a braking impulse regardless of stride length. The fix for overstriding is increasing cadence slightly or shortening the reach of the foot at contact, not prescribing a specific stride length target.
All subjects showed a U-shaped relationship between stride length and VO₂ with an individual optimum. Trained runners self-selected a stride length at or near their metabolic optimum.
This analysis is AI-generated and intended for educational purposes only. It is not a substitute for advice from a qualified running coach or physiotherapist. Biomechanics metrics are estimates from 2D side-view video, not lab-grade measurements.